[v3,2/5] mtd: nand: add NVIDIA Tegra NAND Flash controller driver

Add support for the NAND flash controller found on NVIDIA
Tegra 2/3 SoCs.

Signed-off-by: Thierry Reding <thierry.reding@avionic-design.de>
Signed-off-by: Lucas Stach <dev@lynxeye.de>
Reviewed-by: Stefan Agner <stefan@agner.ch>
---
v2:
- remove Tegra 3 compatible
- remove useless part_probes
- don't store irq number
- use gpiod API instead of deprecated of_gpios
- don't store reset
- correct TIMING_TCS mask
- simplify irq handler
- correct timing calculations
- don't store buswidth
- drop compile test
- correct ECC handling

v3:
- remove superfluous NAND cap setting
- correct ECC layout
- don't flag ECC error for erased pages
- make MTD device name a bit human friendlier
- mark subpage writes as unsupported
- parse BBT on flash property
---
 MAINTAINERS                   |   6 +
 drivers/mtd/nand/Kconfig      |   6 +
 drivers/mtd/nand/Makefile     |   1 +
 drivers/mtd/nand/tegra_nand.c | 801 ++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 814 insertions(+)
 create mode 100644 drivers/mtd/nand/tegra_nand.c

Hi Lucas,

On Sun, May 10, 2015 at 08:29:59PM +0200, Lucas Stach wrote:
> Add support for the NAND flash controller found on NVIDIA
> Tegra 2/3 SoCs.
> 
> Signed-off-by: Thierry Reding <thierry.reding@avionic-design.de>
> Signed-off-by: Lucas Stach <dev@lynxeye.de>
> Reviewed-by: Stefan Agner <stefan@agner.ch>
> ---
> v2:
> - remove Tegra 3 compatible
> - remove useless part_probes
> - don't store irq number
> - use gpiod API instead of deprecated of_gpios
> - don't store reset
> - correct TIMING_TCS mask
> - simplify irq handler
> - correct timing calculations
> - don't store buswidth
> - drop compile test
> - correct ECC handling
> 
> v3:
> - remove superfluous NAND cap setting
> - correct ECC layout
> - don't flag ECC error for erased pages

^^ So you approached a tricky subject here :) more below

> - make MTD device name a bit human friendlier
> - mark subpage writes as unsupported
> - parse BBT on flash property
> ---
>  MAINTAINERS                   |   6 +
>  drivers/mtd/nand/Kconfig      |   6 +
>  drivers/mtd/nand/Makefile     |   1 +
>  drivers/mtd/nand/tegra_nand.c | 801 ++++++++++++++++++++++++++++++++++++++++++
>  4 files changed, 814 insertions(+)
>  create mode 100644 drivers/mtd/nand/tegra_nand.c
> 
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 781e099..7e5551f 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -9747,6 +9747,12 @@ M:	Laxman Dewangan <ldewangan@nvidia.com>
>  S:	Supported
>  F:	drivers/input/keyboard/tegra-kbc.c
>  
> +TEGRA NAND DRIVER
> +M:	Lucas Stach <dev@lynxeye.de>
> +S:	Maintained
> +F:	Documentation/devicetree/bindings/mtd/nvidia,tegra20-nand.txt
> +F:	drivers/mtd/nand/tegra_nand.c

Thanks for doing this.

> +
>  TEGRA PWM DRIVER
>  M:	Thierry Reding <thierry.reding@gmail.com>
>  S:	Supported
> diff --git a/drivers/mtd/nand/Kconfig b/drivers/mtd/nand/Kconfig
> index 5897d8d..2696418 100644
> --- a/drivers/mtd/nand/Kconfig
> +++ b/drivers/mtd/nand/Kconfig
> @@ -530,4 +530,10 @@ config MTD_NAND_HISI504
>  	help
>  	  Enables support for NAND controller on Hisilicon SoC Hip04.
>  
> +config MTD_NAND_TEGRA
> +	tristate "Support for NAND on NVIDIA Tegra"
> +	depends on ARCH_TEGRA

Is this a strict depends? Maybe relax to the following at least:

	depends on ARCH_TEGRA || COMPILE_TEST

> +	help
> +	  Enables support for NAND flash on NVIDIA Tegra SoC based boards.
> +
>  endif # MTD_NAND
> diff --git a/drivers/mtd/nand/Makefile b/drivers/mtd/nand/Makefile
> index 582bbd05..3228e6e 100644
> --- a/drivers/mtd/nand/Makefile
> +++ b/drivers/mtd/nand/Makefile
> @@ -52,5 +52,6 @@ obj-$(CONFIG_MTD_NAND_XWAY)		+= xway_nand.o
>  obj-$(CONFIG_MTD_NAND_BCM47XXNFLASH)	+= bcm47xxnflash/
>  obj-$(CONFIG_MTD_NAND_SUNXI)		+= sunxi_nand.o
>  obj-$(CONFIG_MTD_NAND_HISI504)	        += hisi504_nand.o
> +obj-$(CONFIG_MTD_NAND_TEGRA)		+= tegra_nand.o
>  
>  nand-objs := nand_base.o nand_bbt.o nand_timings.o
> diff --git a/drivers/mtd/nand/tegra_nand.c b/drivers/mtd/nand/tegra_nand.c
> new file mode 100644
> index 0000000..20ea1f1
> --- /dev/null
> +++ b/drivers/mtd/nand/tegra_nand.c
> @@ -0,0 +1,801 @@
> +/*
> + * Copyright (C) 2014-2015 Lucas Stach <dev@lynxeye.de>
> + * Copyright (C) 2012 Avionic Design GmbH
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 as
> + * published by the Free Software Foundation.
> + */
> +
> +#include <linux/clk.h>
> +#include <linux/completion.h>
> +#include <linux/delay.h>
> +#include <linux/dma-mapping.h>
> +#include <linux/err.h>
> +#include <linux/gpio/consumer.h>
> +#include <linux/interrupt.h>
> +#include <linux/io.h>
> +#include <linux/module.h>
> +#include <linux/mtd/nand.h>
> +#include <linux/mtd/partitions.h>
> +#include <linux/of_mtd.h>
> +#include <linux/of.h>
> +#include <linux/platform_device.h>
> +#include <linux/reset.h>
> +
> +#define CMD				0x00
> +#define   CMD_GO			(1 << 31)
> +#define   CMD_CLE			(1 << 30)
> +#define   CMD_ALE			(1 << 29)
> +#define   CMD_PIO			(1 << 28)
> +#define   CMD_TX			(1 << 27)
> +#define   CMD_RX			(1 << 26)
> +#define   CMD_SEC_CMD			(1 << 25)
> +#define   CMD_AFT_DAT			(1 << 24)
> +#define   CMD_TRANS_SIZE(x)		(((x) & 0xf) << 20)
> +#define   CMD_A_VALID			(1 << 19)
> +#define   CMD_B_VALID			(1 << 18)
> +#define   CMD_RD_STATUS_CHK		(1 << 17)
> +#define   CMD_RBSY_CHK			(1 << 16)
> +#define   CMD_CE(x)			(1 << (8 + ((x) & 0x7)))
> +#define   CMD_CLE_SIZE(x)		(((x) & 0x3) << 4)
> +#define   CMD_ALE_SIZE(x)		(((x) & 0xf) << 0)
> +
> +#define STATUS				0x04
> +
> +#define ISR				0x08
> +#define   ISR_UND			(1 << 7)
> +#define   ISR_OVR			(1 << 6)
> +#define   ISR_CMD_DONE			(1 << 5)
> +#define   ISR_ECC_ERR			(1 << 4)
> +
> +#define IER				0x0c
> +#define   IER_ERR_TRIG_VAL(x)		(((x) & 0xf) << 16)
> +#define   IER_UND			(1 << 7)
> +#define   IER_OVR			(1 << 6)
> +#define   IER_CMD_DONE			(1 << 5)
> +#define   IER_ECC_ERR			(1 << 4)
> +#define   IER_GIE			(1 << 0)
> +
> +#define CFG				0x10
> +#define   CFG_HW_ECC			(1 << 31)
> +#define   CFG_ECC_SEL			(1 << 30)
> +#define   CFG_ERR_COR			(1 << 29)
> +#define   CFG_PIPE_EN			(1 << 28)
> +#define   CFG_TVAL_4			(0 << 24)
> +#define   CFG_TVAL_6			(1 << 24)
> +#define   CFG_TVAL_8			(2 << 24)
> +#define   CFG_SKIP_SPARE		(1 << 23)
> +#define   CFG_BUS_WIDTH_8		(0 << 21)
> +#define   CFG_BUS_WIDTH_16		(1 << 21)
> +#define   CFG_COM_BSY			(1 << 20)
> +#define   CFG_PS_256			(0 << 16)
> +#define   CFG_PS_512			(1 << 16)
> +#define   CFG_PS_1024			(2 << 16)
> +#define   CFG_PS_2048			(3 << 16)
> +#define   CFG_PS_4096			(4 << 16)
> +#define   CFG_SKIP_SPARE_SIZE_4		(0 << 14)
> +#define   CFG_SKIP_SPARE_SIZE_8		(1 << 14)
> +#define   CFG_SKIP_SPARE_SIZE_12	(2 << 14)
> +#define   CFG_SKIP_SPARE_SIZE_16	(3 << 14)
> +#define   CFG_TAG_BYTE_SIZE(x)		((x) & 0xff)
> +
> +#define TIMING_1			0x14
> +#define   TIMING_TRP_RESP(x)		(((x) & 0xf) << 28)
> +#define   TIMING_TWB(x)			(((x) & 0xf) << 24)
> +#define   TIMING_TCR_TAR_TRR(x)		(((x) & 0xf) << 20)
> +#define   TIMING_TWHR(x)		(((x) & 0xf) << 16)
> +#define   TIMING_TCS(x)			(((x) & 0x3) << 14)
> +#define   TIMING_TWH(x)			(((x) & 0x3) << 12)
> +#define   TIMING_TWP(x)			(((x) & 0xf) <<  8)
> +#define   TIMING_TRH(x)			(((x) & 0xf) <<  4)
> +#define   TIMING_TRP(x)			(((x) & 0xf) <<  0)
> +
> +#define RESP				0x18
> +
> +#define TIMING_2			0x1c
> +#define   TIMING_TADL(x)		((x) & 0xf)
> +
> +#define CMD_1				0x20
> +#define CMD_2				0x24
> +#define ADDR_1				0x28
> +#define ADDR_2				0x2c
> +
> +#define DMA_CTRL			0x30
> +#define   DMA_CTRL_GO			(1 << 31)
> +#define   DMA_CTRL_IN			(0 << 30)
> +#define   DMA_CTRL_OUT			(1 << 30)
> +#define   DMA_CTRL_PERF_EN		(1 << 29)
> +#define   DMA_CTRL_IE_DONE		(1 << 28)
> +#define   DMA_CTRL_REUSE		(1 << 27)
> +#define   DMA_CTRL_BURST_1		(2 << 24)
> +#define   DMA_CTRL_BURST_4		(3 << 24)
> +#define   DMA_CTRL_BURST_8		(4 << 24)
> +#define   DMA_CTRL_BURST_16		(5 << 24)
> +#define   DMA_CTRL_IS_DONE		(1 << 20)
> +#define   DMA_CTRL_EN_A			(1 <<  2)
> +#define   DMA_CTRL_EN_B			(1 <<  1)
> +
> +#define DMA_CFG_A			0x34
> +#define DMA_CFG_B			0x38
> +
> +#define FIFO_CTRL			0x3c
> +#define   FIFO_CTRL_CLR_ALL		(1 << 3)
> +
> +#define DATA_PTR			0x40
> +#define TAG_PTR				0x44
> +#define ECC_PTR				0x48
> +
> +#define DEC_STATUS			0x4c
> +#define   DEC_STATUS_A_ECC_FAIL		(1 << 1)
> +#define   DEC_STATUS_ERR_COUNT_MASK	0x00ff0000
> +#define   DEC_STATUS_ERR_COUNT_SHIFT	16
> +
> +#define HWSTATUS_CMD			0x50
> +#define HWSTATUS_MASK			0x54
> +#define   HWSTATUS_RDSTATUS_MASK(x)	(((x) & 0xff) << 24)
> +#define   HWSTATUS_RDSTATUS_VALUE(x)	(((x) & 0xff) << 16)
> +#define   HWSTATUS_RBSY_MASK(x)		(((x) & 0xff) << 8)
> +#define   HWSTATUS_RBSY_VALUE(x)	(((x) & 0xff) << 0)
> +
> +struct tegra_nand {
> +	void __iomem *regs;
> +	struct clk *clk;
> +	struct gpio_desc *wp_gpio;
> +
> +	struct nand_chip chip;
> +	struct mtd_info mtd;
> +	struct device *dev;
> +
> +	struct completion command_complete;
> +	struct completion dma_complete;
> +
> +	dma_addr_t data_dma;
> +	void *data_buf;
> +	dma_addr_t oob_dma;
> +	void *oob_buf;
> +
> +	int cur_chip;
> +};
> +
> +static inline struct tegra_nand *to_tegra_nand(struct mtd_info *mtd)
> +{
> +	return container_of(mtd, struct tegra_nand, mtd);
> +}
> +
> +static struct nand_ecclayout tegra_nand_oob_16 = {
> +	.eccbytes = 4,
> +	.eccpos = { 4, 5, 6, 7 },
> +	.oobfree = {
> +		{ .offset = 8, . length = 8 }
> +	}
> +};
> +
> +static struct nand_ecclayout tegra_nand_oob_64 = {
> +	.eccbytes = 36,
> +	.eccpos = {
> +		 4,  5,  6,  7,  8,  9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19,
> +		20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35,
> +		36, 37, 38, 39
> +	},
> +	.oobfree = {
> +		{ .offset = 40, .length = 24 }
> +	}
> +};
> +
> +static struct nand_ecclayout tegra_nand_oob_128 = {
> +	.eccbytes = 72,
> +	.eccpos = {
> +		 4,  5,  6,  7,  8,  9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19,
> +		20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35,
> +		36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51,
> +		52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67,
> +		68, 69, 70, 71, 72, 73, 74, 75
> +	},
> +	.oobfree = {
> +		{ .offset = 76, .length = 52 }
> +	}
> +};
> +
> +static struct nand_ecclayout tegra_nand_oob_224 = {
> +	.eccbytes = 144,
> +	.eccpos = {
> +		  4,   5,   6,   7,   8,   9,  10,  11,  12,  13,  14,  15,  16,
> +		 17,  18,  19,  20,  21,  22,  23,  24,  25,  26,  27,  28,  29,
> +		 30,  31,  32,  33,  34,  35,  36,  37,  38,  39,  40,  41,  42,
> +		 43,  44,  45,  46,  47,  48,  49,  50,  51,  52,  53,  54,  55,
> +		 56,  57,  58,  59,  60,  61,  62,  63,  64,  65,  66,  67,  68,
> +		 69,  70,  71,  72,  73,  74,  75,  76,  77,  78,  79,  80,  81,
> +		 82,  83,  84,  85,  86,  87,  88,  89,  90,  91,  92,  93,  94,
> +		 95,  96,  97,  98,  99, 100, 101, 102, 103, 104, 105, 106, 107,
> +		108, 109, 110, 111, 112, 113, 114, 115, 116, 117, 118, 119, 120,
> +		121, 122, 123, 124, 125, 126, 127, 128, 129, 130, 131, 132, 133,
> +		134, 135, 136, 137, 138, 139, 140, 141, 142, 143, 144, 145, 146,
> +		147
> +	},
> +	.oobfree = {
> +		{ .offset = 148, .length = 76 }
> +	}
> +};
> +
> +static irqreturn_t tegra_nand_irq(int irq, void *data)
> +{
> +	struct tegra_nand *nand = data;
> +	u32 isr, dma;
> +
> +	isr = readl(nand->regs + ISR);
> +	dma = readl(nand->regs + DMA_CTRL);
> +
> +	if (!isr && !(dma & DMA_CTRL_IS_DONE))
> +		return IRQ_NONE;
> +
> +	if (isr & ISR_CMD_DONE)
> +		complete(&nand->command_complete);
> +
> +	if (isr & ISR_UND)
> +		dev_dbg(nand->dev, "FIFO underrun\n");
> +
> +	if (isr & ISR_OVR)
> +		dev_dbg(nand->dev, "FIFO overrun\n");
> +
> +	/* handle DMA interrupts */
> +	if (dma & DMA_CTRL_IS_DONE) {
> +		writel(dma, nand->regs + DMA_CTRL);
> +		complete(&nand->dma_complete);
> +	}
> +
> +	/* clear interrupts */
> +	writel(isr, nand->regs + ISR);
> +
> +	return IRQ_HANDLED;
> +}
> +
> +static void tegra_nand_command(struct mtd_info *mtd, unsigned int command,
> +			       int column, int page_addr)
> +{
> +	struct tegra_nand *nand = to_tegra_nand(mtd);
> +	u32 value;
> +
> +	switch (command) {
> +	case NAND_CMD_READOOB:
> +		column += mtd->writesize;
> +		/* fall-through */
> +
> +	case NAND_CMD_READ0:
> +		writel(NAND_CMD_READ0, nand->regs + CMD_1);
> +		writel(NAND_CMD_READSTART, nand->regs + CMD_2);
> +
> +		value = (page_addr << 16) | (column & 0xffff);
> +		writel(value, nand->regs + ADDR_1);
> +
> +		value = page_addr >> 16;
> +		writel(value, nand->regs + ADDR_2);
> +
> +		value = CMD_CLE | CMD_ALE | CMD_ALE_SIZE(4) | CMD_SEC_CMD |
> +			CMD_RBSY_CHK | CMD_CE(nand->cur_chip) | CMD_GO;
> +		writel(value, nand->regs + CMD);
> +		break;
> +
> +	case NAND_CMD_SEQIN:
> +		writel(NAND_CMD_SEQIN, nand->regs + CMD_1);
> +
> +		value = (page_addr << 16) | (column & 0xffff);
> +		writel(value, nand->regs + ADDR_1);
> +
> +		value = page_addr >> 16;
> +		writel(value, nand->regs + ADDR_2);
> +
> +		value = CMD_CLE | CMD_ALE | CMD_ALE_SIZE(4) |
> +			CMD_CE(nand->cur_chip) | CMD_GO;
> +		writel(value, nand->regs + CMD);
> +		break;
> +
> +	case NAND_CMD_PAGEPROG:
> +		writel(NAND_CMD_PAGEPROG, nand->regs + CMD_1);
> +
> +		value = CMD_CLE | CMD_CE(nand->cur_chip) | CMD_GO;
> +		writel(value, nand->regs + CMD);
> +		break;
> +
> +	case NAND_CMD_READID:
> +		writel(NAND_CMD_READID, nand->regs + CMD_1);
> +		writel(column & 0xff, nand->regs + ADDR_1);
> +
> +		value = CMD_GO | CMD_CLE | CMD_ALE | CMD_CE(nand->cur_chip);
> +		writel(value, nand->regs + CMD);
> +		break;
> +
> +	case NAND_CMD_ERASE1:
> +		writel(NAND_CMD_ERASE1, nand->regs + CMD_1);
> +		writel(NAND_CMD_ERASE2, nand->regs + CMD_2);
> +		writel(page_addr, nand->regs + ADDR_1);
> +
> +		value = CMD_GO | CMD_CLE | CMD_ALE | CMD_ALE_SIZE(2) |
> +			CMD_SEC_CMD | CMD_RBSY_CHK | CMD_CE(nand->cur_chip);
> +		writel(value, nand->regs + CMD);
> +		break;
> +
> +	case NAND_CMD_ERASE2:
> +		return;
> +
> +	case NAND_CMD_STATUS:
> +		writel(NAND_CMD_STATUS, nand->regs + CMD_1);
> +
> +		value = CMD_GO | CMD_CLE | CMD_CE(nand->cur_chip);
> +		writel(value, nand->regs + CMD);
> +		break;
> +
> +	case NAND_CMD_PARAM:
> +		writel(NAND_CMD_PARAM, nand->regs + CMD_1);
> +		writel(column & 0xff, nand->regs + ADDR_1);
> +		value = CMD_GO | CMD_CLE | CMD_ALE | CMD_CE(nand->cur_chip);
> +		writel(value, nand->regs + CMD);
> +		break;
> +
> +	case NAND_CMD_RESET:
> +		writel(NAND_CMD_RESET, nand->regs + CMD_1);
> +
> +		value = CMD_GO | CMD_CLE | CMD_CE(nand->cur_chip);
> +		writel(value, nand->regs + CMD);
> +		break;
> +
> +	default:
> +		dev_warn(nand->dev, "unsupported command: %x\n", command);
> +		return;
> +	}
> +
> +	wait_for_completion(&nand->command_complete);
> +}
> +
> +static void tegra_nand_select_chip(struct mtd_info *mtd, int chip)
> +{
> +	struct tegra_nand *nand = to_tegra_nand(mtd);
> +
> +	nand->cur_chip = chip;
> +}
> +
> +static uint8_t tegra_nand_read_byte(struct mtd_info *mtd)
> +{
> +	struct tegra_nand *nand = to_tegra_nand(mtd);
> +	u32 value;
> +
> +	value = CMD_TRANS_SIZE(0) | CMD_CE(nand->cur_chip) |
> +		CMD_PIO | CMD_RX | CMD_A_VALID | CMD_GO;
> +
> +	writel(value, nand->regs + CMD);
> +	wait_for_completion(&nand->command_complete);
> +
> +	return readl(nand->regs + RESP) & 0xff;
> +}
> +
> +static void tegra_nand_read_buf(struct mtd_info *mtd, uint8_t *buffer,
> +				int length)
> +{
> +	struct tegra_nand *nand = to_tegra_nand(mtd);
> +	size_t i;
> +
> +	for (i = 0; i < length; i += 4) {
> +		u32 value;
> +		size_t n = min_t(size_t, length - i, 4);
> +
> +		value = CMD_GO | CMD_PIO | CMD_RX | CMD_A_VALID |
> +			CMD_CE(nand->cur_chip) | CMD_TRANS_SIZE(n - 1);
> +
> +		writel(value, nand->regs + CMD);
> +		wait_for_completion(&nand->command_complete);
> +
> +		value = readl(nand->regs + RESP);
> +		memcpy(buffer + i, &value, n);
> +	}
> +}
> +
> +static void tegra_nand_write_buf(struct mtd_info *mtd, const uint8_t *buffer,
> +				 int length)
> +{
> +	struct tegra_nand *nand = to_tegra_nand(mtd);
> +	size_t i;
> +
> +	for (i = 0; i < length; i += 4) {
> +		u32 value;
> +		size_t n = min_t(size_t, length - i, 4);
> +
> +		memcpy(&value, buffer + i, n);
> +		writel(value, nand->regs + RESP);
> +
> +		value = CMD_GO | CMD_PIO | CMD_TX | CMD_A_VALID |
> +			CMD_CE(nand->cur_chip) | CMD_TRANS_SIZE(n - 1);
> +
> +		writel(value, nand->regs + CMD);
> +		wait_for_completion(&nand->command_complete);
> +	}
> +}
> +
> +static int tegra_nand_read_page(struct mtd_info *mtd, struct nand_chip *chip,
> +				uint8_t *buf, int oob_required, int page)
> +{
> +	struct tegra_nand *nand = to_tegra_nand(mtd);
> +	u32 value;
> +
> +	value = readl(nand->regs + CFG);
> +	value |= CFG_HW_ECC | CFG_ERR_COR;
> +	writel(value, nand->regs + CFG);
> +
> +	writel(mtd->writesize - 1, nand->regs + DMA_CFG_A);
> +	writel(nand->data_dma, nand->regs + DATA_PTR);
> +
> +	if (oob_required) {
> +		writel(mtd->oobsize - 1, nand->regs + DMA_CFG_B);
> +		writel(nand->oob_dma, nand->regs + TAG_PTR);
> +	} else {
> +		writel(0, nand->regs + DMA_CFG_B);
> +		writel(0, nand->regs + TAG_PTR);
> +	}
> +
> +	value = DMA_CTRL_GO | DMA_CTRL_IN | DMA_CTRL_PERF_EN |
> +		DMA_CTRL_REUSE | DMA_CTRL_IE_DONE | DMA_CTRL_IS_DONE |
> +		DMA_CTRL_BURST_8 | DMA_CTRL_EN_A;
> +
> +	if (oob_required)
> +		value |= DMA_CTRL_EN_B;
> +
> +	writel(value, nand->regs + DMA_CTRL);
> +
> +	value = CMD_GO | CMD_RX | CMD_TRANS_SIZE(8) |
> +		CMD_A_VALID | CMD_CE(nand->cur_chip);
> +	if (oob_required)
> +		value |= CMD_B_VALID;
> +	writel(value, nand->regs + CMD);
> +
> +	wait_for_completion(&nand->command_complete);
> +	wait_for_completion(&nand->dma_complete);
> +
> +	if (oob_required)
> +		memcpy(chip->oob_poi, nand->oob_buf, mtd->oobsize);
> +	memcpy(buf, nand->data_buf, mtd->writesize);
> +
> +	value = readl(nand->regs + CFG);
> +	value &= ~(CFG_HW_ECC | CFG_ERR_COR);
> +	writel(value, nand->regs + CFG);
> +
> +	value = readl(nand->regs + DEC_STATUS);
> +
> +	if (value & DEC_STATUS_A_ECC_FAIL) {
> +		/*
> +		 * The ECC isn't smart enough to figure out if a page is
> +		 * completely erased and flags an error in this case. So we
> +		 * check the read data here to figure out if it's a legitimate
> +		 * error or a false positive.
> +		 */
> +		int i;
> +		u32 *data = (u32 *)buf;
> +		for (i = 0; i < mtd->writesize / 4; i++) {
> +			if (data[i] != 0xffffffff) {
> +				mtd->ecc_stats.failed++;
> +				return -EBADMSG;
> +			}
> +		}

Hmm, what about OOB? It's possible to actually write 0xff to the entire
page. This hunk means that such a data pattern would then be
unprotected. You should probably check that *both* the main and OOB data
are all 0xff; if there are non-0xff bytes, then that (probably, see the
following) means someone intentionally wrote all 0xff to the page. [1]

Also, your check doesn't handle the case of finding bitflips in erased
pages. So not only do you need to check for all 0xff, but you also need
to tolerate a few flips. e.g., using hweight*() functions. There is
plenty of discussion on this subject, as many people have tried to
resolve this for their various drivers. But none have really done this
in a thorough and correct way, so few have been merged. Thus, I'd really
like to get something like this merged to nand_base.c, with a NAND_*
flag or two to enable it. That would help drivers like yours to easily
grab a good (albeit, likely slow) implementation.

So, I'd like to see the first request (about OOB checks) solved, and if
the larger bitflips-in-erased-pages issue isn't addressed, please
include a FIXME comment, or something similar.

> +		return 0;
> +	}
> +
> +	if (value & DEC_STATUS_ERR_COUNT_MASK) {
> +		value = (value & DEC_STATUS_ERR_COUNT_MASK) >>
> +			DEC_STATUS_ERR_COUNT_SHIFT;

What does this ERR_COUNT represent? The total bitflips seen in this
page? The max seen per ECC region? Or something else?

> +		mtd->ecc_stats.corrected += value;

I ask because this ^^^ should be accounting the total bitflips for the
page, if possible...

> +		return value;

...and this ^^^ should be returning the max bitflips seen in a single
correction region (see the mtd_read() API). There is a subtle
difference.

> +	}
> +
> +	return 0;
> +}
> +
> +static int tegra_nand_write_page(struct mtd_info *mtd, struct nand_chip *chip,
> +				 const uint8_t *buf, int oob_required)
> +{
> +	struct tegra_nand *nand = to_tegra_nand(mtd);
> +	unsigned long value;
> +
> +	value = readl(nand->regs + CFG);
> +	value |= CFG_HW_ECC | CFG_ERR_COR;
> +	writel(value, nand->regs + CFG);
> +
> +	memcpy(nand->data_buf, buf, mtd->writesize);
> +
> +	writel(mtd->writesize - 1, nand->regs + DMA_CFG_A);
> +	writel(nand->data_dma, nand->regs + DATA_PTR);
> +
> +	writel(0, nand->regs + DMA_CFG_B);
> +	writel(0, nand->regs + TAG_PTR);
> +
> +	value = DMA_CTRL_GO | DMA_CTRL_OUT | DMA_CTRL_PERF_EN |
> +		DMA_CTRL_IE_DONE | DMA_CTRL_IS_DONE |
> +		DMA_CTRL_BURST_8 | DMA_CTRL_EN_A;
> +	writel(value, nand->regs + DMA_CTRL);
> +
> +	value = CMD_GO | CMD_TX | CMD_A_VALID | CMD_TRANS_SIZE(8) |
> +		CMD_CE(nand->cur_chip);
> +	writel(value, nand->regs + CMD);
> +
> +	wait_for_completion(&nand->command_complete);
> +	wait_for_completion(&nand->dma_complete);
> +
> +	value = readl(nand->regs + CFG);
> +	value &= ~(CFG_HW_ECC | CFG_ERR_COR);
> +	writel(value, nand->regs + CFG);
> +
> +	return 0;
> +}
> +
> +static void tegra_nand_setup_timing(struct tegra_nand *nand, int mode)
> +{

This function could use some comments. The math can be easy to get
wrong, especially without the annotation of units (e.g., picoseconds).
Also, look out for rounding inaccuracies. DIV_ROUND_UP() is nice for
getting conservative conversions at times.

> +	unsigned long rate = clk_get_rate(nand->clk) / 1000000;
> +	unsigned long period = 1000000 / rate;
> +	const struct nand_sdr_timings *timings;
> +	u32 val, reg = 0;
> +
> +	timings = onfi_async_timing_mode_to_sdr_timings(mode);
> +
> +	val = max3(timings->tAR_min, timings->tRR_min,
> +		   timings->tRC_min) / period;
> +	if (val > 2)
> +		val -= 3;
> +	reg |= TIMING_TCR_TAR_TRR(val);
> +
> +	val = max(max(timings->tCS_min, timings->tCH_min),
> +		  max(timings->tALS_min, timings->tALH_min)) / period;
> +	if (val > 1)
> +		val -= 2;
> +	reg |= TIMING_TCS(val);
> +
> +	val = (max(timings->tRP_min, timings->tREA_max) + 6000) / period;
> +	reg |= (TIMING_TRP(val) | TIMING_TRP_RESP(val));
> +
> +	reg |= TIMING_TWB(timings->tWB_max / period);
> +	reg |= TIMING_TWHR(timings->tWHR_min / period);
> +	reg |= TIMING_TWH(timings->tWH_min / period);
> +	reg |= TIMING_TWP(timings->tWP_min / period);
> +	reg |= TIMING_TRH(timings->tRHW_min / period);
> +
> +	writel(reg, nand->regs + TIMING_1);
> +
> +	val = timings->tADL_min / period;
> +	if (val > 2)
> +		val -= 3;
> +	reg = TIMING_TADL(val);
> +
> +	writel(reg, nand->regs + TIMING_2);
> +}
> +
> +static void tegra_nand_setup_chiptiming(struct tegra_nand *nand)
> +{
> +	struct nand_chip *chip = &nand->chip;
> +	int mode;
> +
> +	mode = onfi_get_async_timing_mode(chip);
> +	if (mode == ONFI_TIMING_MODE_UNKNOWN)
> +		mode = chip->onfi_timing_mode_default;
> +	else
> +		mode = fls(mode);
> +
> +	tegra_nand_setup_timing(nand, mode);
> +}
> +
> +static int tegra_nand_probe(struct platform_device *pdev)
> +{
> +	struct reset_control *rst;
> +	struct tegra_nand *nand;
> +	struct nand_chip *chip;
> +	struct mtd_info *mtd;
> +	struct resource *res;
> +	unsigned long value;
> +	int irq, buswidth, err = 0;
> +
> +	nand = devm_kzalloc(&pdev->dev, sizeof(*nand), GFP_KERNEL);
> +	if (!nand)
> +		return -ENOMEM;
> +
> +	nand->dev = &pdev->dev;
> +
> +	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
> +	nand->regs = devm_ioremap_resource(&pdev->dev, res);
> +	if (IS_ERR(nand->regs))
> +		return PTR_ERR(nand->regs);
> +
> +	irq = platform_get_irq(pdev, 0);
> +	err = devm_request_irq(&pdev->dev, irq, tegra_nand_irq, 0,
> +			       dev_name(&pdev->dev), nand);
> +	if (err)
> +		return err;
> +
> +	rst = devm_reset_control_get(&pdev->dev, "nand");
> +	if (IS_ERR(rst))
> +		return PTR_ERR(rst);
> +
> +	nand->clk = devm_clk_get(&pdev->dev, "nand");
> +	if (IS_ERR(nand->clk))
> +		return PTR_ERR(nand->clk);
> +
> +	nand->wp_gpio = gpiod_get_optional(&pdev->dev, "nvidia,wp-gpios",
> +					   GPIOD_OUT_HIGH);
> +	if (IS_ERR(nand->wp_gpio))
> +		return PTR_ERR(nand->wp_gpio);
> +
> +	buswidth = of_get_nand_bus_width(pdev->dev.of_node);
> +	if (buswidth < 0)
> +		return buswidth;

You could set chip->dn, then nand_dt_init() might capture this for you.

> +
> +	err = clk_prepare_enable(nand->clk);
> +	if (err)
> +		return err;
> +
> +	reset_control_assert(rst);
> +	udelay(2);
> +	reset_control_deassert(rst);
> +
> +	value = HWSTATUS_RDSTATUS_MASK(1) | HWSTATUS_RDSTATUS_VALUE(0) |
> +		HWSTATUS_RBSY_MASK(NAND_STATUS_READY) |
> +		HWSTATUS_RBSY_VALUE(NAND_STATUS_READY);
> +	writel(NAND_CMD_STATUS, nand->regs + HWSTATUS_CMD);
> +	writel(value, nand->regs + HWSTATUS_MASK);
> +
> +	init_completion(&nand->command_complete);
> +	init_completion(&nand->dma_complete);
> +
> +	mtd = &nand->mtd;
> +	mtd->name = "tegra_nand";
> +	mtd->owner = THIS_MODULE;
> +	mtd->priv = &nand->chip;
> +
> +	/* clear interrupts */
> +	value = readl(nand->regs + ISR);
> +	writel(value, nand->regs + ISR);
> +
> +	writel(DMA_CTRL_IS_DONE, nand->regs + DMA_CTRL);
> +
> +	/* enable interrupts */
> +	value = IER_UND | IER_OVR | IER_CMD_DONE | IER_ECC_ERR | IER_GIE;
> +	writel(value, nand->regs + IER);
> +
> +	value = 0;
> +	if (buswidth == 16)
> +		value |= CFG_BUS_WIDTH_16;
> +	writel(value, nand->regs + CFG);
> +
> +	chip = &nand->chip;
> +	chip->options = NAND_NO_SUBPAGE_WRITE;
> +	chip->cmdfunc = tegra_nand_command;
> +	chip->select_chip = tegra_nand_select_chip;
> +	chip->read_byte = tegra_nand_read_byte;
> +	chip->read_buf = tegra_nand_read_buf;
> +	chip->write_buf = tegra_nand_write_buf;
> +
> +	if (of_get_nand_on_flash_bbt(pdev->dev.of_node))
> +		chip->bbt_options = NAND_BBT_USE_FLASH | NAND_BBT_NO_OOB;

Again, nand_dt_init() might help you. You might then augment it with:

	if (chip->bbt_options & NAND_BBT_USE_FLASH)
		chip->bbt_options |= NAND_BBT_NO_OOB;

> +
> +	tegra_nand_setup_timing(nand, 0);
> +
> +	err = nand_scan_ident(mtd, 1, NULL);
> +	if (err)
> +		return err;
> +
> +	nand->data_buf = dmam_alloc_coherent(&pdev->dev, mtd->writesize,
> +					    &nand->data_dma, GFP_KERNEL);
> +	if (!nand->data_buf)
> +		return -ENOMEM;
> +
> +	nand->oob_buf = dmam_alloc_coherent(&pdev->dev, mtd->oobsize,
> +					    &nand->oob_dma, GFP_KERNEL);
> +	if (!nand->oob_buf)
> +		return -ENOMEM;
> +
> +	chip->ecc.mode = NAND_ECC_HW;
> +	chip->ecc.size = 512;
> +	chip->ecc.bytes = mtd->oobsize;
> +	chip->ecc.read_page = tegra_nand_read_page;
> +	chip->ecc.write_page = tegra_nand_write_page;
> +
> +	value = readl(nand->regs + CFG);
> +	value |=  CFG_PIPE_EN | CFG_SKIP_SPARE | CFG_SKIP_SPARE_SIZE_4;
> +
> +	switch (mtd->oobsize) {
> +	case 16:
> +		chip->ecc.layout = &tegra_nand_oob_16;
> +		chip->ecc.strength = 1;
> +		value |= CFG_TAG_BYTE_SIZE(tegra_nand_oob_16.oobfree[0].length
> +			 - 1);
> +		break;
> +	case 64:
> +		chip->ecc.layout = &tegra_nand_oob_64;
> +		chip->ecc.strength = 8;
> +		value |= CFG_ECC_SEL | CFG_TVAL_8 |
> +			 CFG_TAG_BYTE_SIZE(tegra_nand_oob_64.oobfree[0].length
> +			 - 1);
> +		break;
> +	case 128:
> +		chip->ecc.layout = &tegra_nand_oob_128;
> +		chip->ecc.strength = 8;
> +		value |= CFG_ECC_SEL | CFG_TVAL_8 |
> +			 CFG_TAG_BYTE_SIZE(tegra_nand_oob_128.oobfree[0].length
> +			 - 1);
> +		break;
> +	case 224:
> +		chip->ecc.layout = &tegra_nand_oob_224;
> +		chip->ecc.strength = 8;
> +		value |= CFG_ECC_SEL | CFG_TVAL_8 |
> +			 CFG_TAG_BYTE_SIZE(tegra_nand_oob_224.oobfree[0].length
> +			 - 1);
> +		break;
> +	default:
> +		dev_err(&pdev->dev, "unhandled OOB size %d\n", mtd->oobsize);
> +		return -ENODEV;
> +	}
> +
> +	switch (mtd->writesize) {
> +	case 256:
> +		value |= CFG_PS_256;
> +		break;
> +	case 512:
> +		value |= CFG_PS_512;
> +		break;
> +	case 1024:
> +		value |= CFG_PS_1024;
> +		break;
> +	case 2048:
> +		value |= CFG_PS_2048;
> +		break;
> +	case 4096:
> +		value |= CFG_PS_4096;
> +		break;
> +	default:
> +		dev_err(&pdev->dev, "unhandled writesize %d\n", mtd->writesize);
> +		return -ENODEV;
> +	}
> +
> +	writel(value, nand->regs + CFG);
> +
> +	tegra_nand_setup_chiptiming(nand);
> +
> +	err = nand_scan_tail(mtd);
> +	if (err)
> +		return err;
> +
> +	mtd_device_parse_register(mtd, NULL,
> +				  &(struct mtd_part_parser_data) {
> +					.of_node = pdev->dev.of_node,
> +				  },
> +				  NULL, 0);

Check the return value for errors.

> +
> +	platform_set_drvdata(pdev, nand);
> +
> +	return 0;
> +}
> +
> +static int tegra_nand_remove(struct platform_device *pdev)
> +{
> +	struct tegra_nand *nand = platform_get_drvdata(pdev);
> +
> +	nand_release(&nand->mtd);
> +
> +	clk_disable_unprepare(nand->clk);
> +
> +	return 0;
> +}
> +
> +static const struct of_device_id tegra_nand_of_match[] = {
> +	{ .compatible = "nvidia,tegra20-nand" },
> +	{ /* sentinel */ }
> +};
> +
> +static struct platform_driver tegra_nand_driver = {
> +	.driver = {
> +		.name = "tegra-nand",
> +		.of_match_table = tegra_nand_of_match,
> +	},
> +	.probe = tegra_nand_probe,
> +	.remove = tegra_nand_remove,
> +};
> +module_platform_driver(tegra_nand_driver);
> +
> +MODULE_DESCRIPTION("NVIDIA Tegra NAND driver");
> +MODULE_AUTHOR("Thierry Reding <thierry.reding@avionic-design.de");
> +MODULE_AUTHOR("Lucas Stach <dev@lynxeye.de");
> +MODULE_LICENSE("GPL v2");
> +MODULE_DEVICE_TABLE(of, tegra_nand_of_match);

Thanks,
Brian

[1] Litmus test: write all 0xff with nandwrite, then read back with
nanddump. Do you get 'ECC failed' counts? Now that I think about it, we
should probably publish a proper test, either in mtd-utils or
drivers/mtd/tests/ to check for this.
--
To unsubscribe from this list: send the line "unsubscribe linux-tegra" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html

Am Dienstag, den 21.07.2015, 14:27 -0700 schrieb Brian Norris:
> Hi Lucas,
> 
> On Sun, May 10, 2015 at 08:29:59PM +0200, Lucas Stach wrote:
> > Add support for the NAND flash controller found on NVIDIA
> > Tegra 2/3 SoCs.
> > 
> > Signed-off-by: Thierry Reding <thierry.reding@avionic-design.de>
> > Signed-off-by: Lucas Stach <dev@lynxeye.de>
> > Reviewed-by: Stefan Agner <stefan@agner.ch>
> > ---
> > v2:
> > - remove Tegra 3 compatible
> > - remove useless part_probes
> > - don't store irq number
> > - use gpiod API instead of deprecated of_gpios
> > - don't store reset
> > - correct TIMING_TCS mask
> > - simplify irq handler
> > - correct timing calculations
> > - don't store buswidth
> > - drop compile test
> > - correct ECC handling
> > 
> > v3:
> > - remove superfluous NAND cap setting
> > - correct ECC layout
> > - don't flag ECC error for erased pages
> 
> ^^ So you approached a tricky subject here :) more below
> 
> > - make MTD device name a bit human friendlier
> > - mark subpage writes as unsupported
> > - parse BBT on flash property
> > ---
> >  MAINTAINERS                   |   6 +
> >  drivers/mtd/nand/Kconfig      |   6 +
> >  drivers/mtd/nand/Makefile     |   1 +
> >  drivers/mtd/nand/tegra_nand.c | 801 ++++++++++++++++++++++++++++++++++++++++++
> >  4 files changed, 814 insertions(+)
> >  create mode 100644 drivers/mtd/nand/tegra_nand.c
> > 
> > diff --git a/MAINTAINERS b/MAINTAINERS
> > index 781e099..7e5551f 100644
> > --- a/MAINTAINERS
> > +++ b/MAINTAINERS
> > @@ -9747,6 +9747,12 @@ M:	Laxman Dewangan <ldewangan@nvidia.com>
> >  S:	Supported
> >  F:	drivers/input/keyboard/tegra-kbc.c
> >  
> > +TEGRA NAND DRIVER
> > +M:	Lucas Stach <dev@lynxeye.de>
> > +S:	Maintained
> > +F:	Documentation/devicetree/bindings/mtd/nvidia,tegra20-nand.txt
> > +F:	drivers/mtd/nand/tegra_nand.c
> 
> Thanks for doing this.
> 
> > +
> >  TEGRA PWM DRIVER
> >  M:	Thierry Reding <thierry.reding@gmail.com>
> >  S:	Supported
> > diff --git a/drivers/mtd/nand/Kconfig b/drivers/mtd/nand/Kconfig
> > index 5897d8d..2696418 100644
> > --- a/drivers/mtd/nand/Kconfig
> > +++ b/drivers/mtd/nand/Kconfig
> > @@ -530,4 +530,10 @@ config MTD_NAND_HISI504
> >  	help
> >  	  Enables support for NAND controller on Hisilicon SoC Hip04.
> >  
> > +config MTD_NAND_TEGRA
> > +	tristate "Support for NAND on NVIDIA Tegra"
> > +	depends on ARCH_TEGRA
> 
> Is this a strict depends? Maybe relax to the following at least:
> 
> 	depends on ARCH_TEGRA || COMPILE_TEST
> 
> > +	help
> > +	  Enables support for NAND flash on NVIDIA Tegra SoC based boards.
> > +
> >  endif # MTD_NAND
> > diff --git a/drivers/mtd/nand/Makefile b/drivers/mtd/nand/Makefile
> > index 582bbd05..3228e6e 100644
> > --- a/drivers/mtd/nand/Makefile
> > +++ b/drivers/mtd/nand/Makefile
> > @@ -52,5 +52,6 @@ obj-$(CONFIG_MTD_NAND_XWAY)		+= xway_nand.o
> >  obj-$(CONFIG_MTD_NAND_BCM47XXNFLASH)	+= bcm47xxnflash/
> >  obj-$(CONFIG_MTD_NAND_SUNXI)		+= sunxi_nand.o
> >  obj-$(CONFIG_MTD_NAND_HISI504)	        += hisi504_nand.o
> > +obj-$(CONFIG_MTD_NAND_TEGRA)		+= tegra_nand.o
> >  
> >  nand-objs := nand_base.o nand_bbt.o nand_timings.o
> > diff --git a/drivers/mtd/nand/tegra_nand.c b/drivers/mtd/nand/tegra_nand.c
> > new file mode 100644
> > index 0000000..20ea1f1
> > --- /dev/null
> > +++ b/drivers/mtd/nand/tegra_nand.c
> > @@ -0,0 +1,801 @@
> > +/*
> > + * Copyright (C) 2014-2015 Lucas Stach <dev@lynxeye.de>
> > + * Copyright (C) 2012 Avionic Design GmbH
> > + *
> > + * This program is free software; you can redistribute it and/or modify
> > + * it under the terms of the GNU General Public License version 2 as
> > + * published by the Free Software Foundation.
> > + */
> > +
> > +#include <linux/clk.h>
> > +#include <linux/completion.h>
> > +#include <linux/delay.h>
> > +#include <linux/dma-mapping.h>
> > +#include <linux/err.h>
> > +#include <linux/gpio/consumer.h>
> > +#include <linux/interrupt.h>
> > +#include <linux/io.h>
> > +#include <linux/module.h>
> > +#include <linux/mtd/nand.h>
> > +#include <linux/mtd/partitions.h>
> > +#include <linux/of_mtd.h>
> > +#include <linux/of.h>
> > +#include <linux/platform_device.h>
> > +#include <linux/reset.h>
> > +
> > +#define CMD				0x00
> > +#define   CMD_GO			(1 << 31)
> > +#define   CMD_CLE			(1 << 30)
> > +#define   CMD_ALE			(1 << 29)
> > +#define   CMD_PIO			(1 << 28)
> > +#define   CMD_TX			(1 << 27)
> > +#define   CMD_RX			(1 << 26)
> > +#define   CMD_SEC_CMD			(1 << 25)
> > +#define   CMD_AFT_DAT			(1 << 24)
> > +#define   CMD_TRANS_SIZE(x)		(((x) & 0xf) << 20)
> > +#define   CMD_A_VALID			(1 << 19)
> > +#define   CMD_B_VALID			(1 << 18)
> > +#define   CMD_RD_STATUS_CHK		(1 << 17)
> > +#define   CMD_RBSY_CHK			(1 << 16)
> > +#define   CMD_CE(x)			(1 << (8 + ((x) & 0x7)))
> > +#define   CMD_CLE_SIZE(x)		(((x) & 0x3) << 4)
> > +#define   CMD_ALE_SIZE(x)		(((x) & 0xf) << 0)
> > +
> > +#define STATUS				0x04
> > +
> > +#define ISR				0x08
> > +#define   ISR_UND			(1 << 7)
> > +#define   ISR_OVR			(1 << 6)
> > +#define   ISR_CMD_DONE			(1 << 5)
> > +#define   ISR_ECC_ERR			(1 << 4)
> > +
> > +#define IER				0x0c
> > +#define   IER_ERR_TRIG_VAL(x)		(((x) & 0xf) << 16)
> > +#define   IER_UND			(1 << 7)
> > +#define   IER_OVR			(1 << 6)
> > +#define   IER_CMD_DONE			(1 << 5)
> > +#define   IER_ECC_ERR			(1 << 4)
> > +#define   IER_GIE			(1 << 0)
> > +
> > +#define CFG				0x10
> > +#define   CFG_HW_ECC			(1 << 31)
> > +#define   CFG_ECC_SEL			(1 << 30)
> > +#define   CFG_ERR_COR			(1 << 29)
> > +#define   CFG_PIPE_EN			(1 << 28)
> > +#define   CFG_TVAL_4			(0 << 24)
> > +#define   CFG_TVAL_6			(1 << 24)
> > +#define   CFG_TVAL_8			(2 << 24)
> > +#define   CFG_SKIP_SPARE		(1 << 23)
> > +#define   CFG_BUS_WIDTH_8		(0 << 21)
> > +#define   CFG_BUS_WIDTH_16		(1 << 21)
> > +#define   CFG_COM_BSY			(1 << 20)
> > +#define   CFG_PS_256			(0 << 16)
> > +#define   CFG_PS_512			(1 << 16)
> > +#define   CFG_PS_1024			(2 << 16)
> > +#define   CFG_PS_2048			(3 << 16)
> > +#define   CFG_PS_4096			(4 << 16)
> > +#define   CFG_SKIP_SPARE_SIZE_4		(0 << 14)
> > +#define   CFG_SKIP_SPARE_SIZE_8		(1 << 14)
> > +#define   CFG_SKIP_SPARE_SIZE_12	(2 << 14)
> > +#define   CFG_SKIP_SPARE_SIZE_16	(3 << 14)
> > +#define   CFG_TAG_BYTE_SIZE(x)		((x) & 0xff)
> > +
> > +#define TIMING_1			0x14
> > +#define   TIMING_TRP_RESP(x)		(((x) & 0xf) << 28)
> > +#define   TIMING_TWB(x)			(((x) & 0xf) << 24)
> > +#define   TIMING_TCR_TAR_TRR(x)		(((x) & 0xf) << 20)
> > +#define   TIMING_TWHR(x)		(((x) & 0xf) << 16)
> > +#define   TIMING_TCS(x)			(((x) & 0x3) << 14)
> > +#define   TIMING_TWH(x)			(((x) & 0x3) << 12)
> > +#define   TIMING_TWP(x)			(((x) & 0xf) <<  8)
> > +#define   TIMING_TRH(x)			(((x) & 0xf) <<  4)
> > +#define   TIMING_TRP(x)			(((x) & 0xf) <<  0)
> > +
> > +#define RESP				0x18
> > +
> > +#define TIMING_2			0x1c
> > +#define   TIMING_TADL(x)		((x) & 0xf)
> > +
> > +#define CMD_1				0x20
> > +#define CMD_2				0x24
> > +#define ADDR_1				0x28
> > +#define ADDR_2				0x2c
> > +
> > +#define DMA_CTRL			0x30
> > +#define   DMA_CTRL_GO			(1 << 31)
> > +#define   DMA_CTRL_IN			(0 << 30)
> > +#define   DMA_CTRL_OUT			(1 << 30)
> > +#define   DMA_CTRL_PERF_EN		(1 << 29)
> > +#define   DMA_CTRL_IE_DONE		(1 << 28)
> > +#define   DMA_CTRL_REUSE		(1 << 27)
> > +#define   DMA_CTRL_BURST_1		(2 << 24)
> > +#define   DMA_CTRL_BURST_4		(3 << 24)
> > +#define   DMA_CTRL_BURST_8		(4 << 24)
> > +#define   DMA_CTRL_BURST_16		(5 << 24)
> > +#define   DMA_CTRL_IS_DONE		(1 << 20)
> > +#define   DMA_CTRL_EN_A			(1 <<  2)
> > +#define   DMA_CTRL_EN_B			(1 <<  1)
> > +
> > +#define DMA_CFG_A			0x34
> > +#define DMA_CFG_B			0x38
> > +
> > +#define FIFO_CTRL			0x3c
> > +#define   FIFO_CTRL_CLR_ALL		(1 << 3)
> > +
> > +#define DATA_PTR			0x40
> > +#define TAG_PTR				0x44
> > +#define ECC_PTR				0x48
> > +
> > +#define DEC_STATUS			0x4c
> > +#define   DEC_STATUS_A_ECC_FAIL		(1 << 1)
> > +#define   DEC_STATUS_ERR_COUNT_MASK	0x00ff0000
> > +#define   DEC_STATUS_ERR_COUNT_SHIFT	16
> > +
> > +#define HWSTATUS_CMD			0x50
> > +#define HWSTATUS_MASK			0x54
> > +#define   HWSTATUS_RDSTATUS_MASK(x)	(((x) & 0xff) << 24)
> > +#define   HWSTATUS_RDSTATUS_VALUE(x)	(((x) & 0xff) << 16)
> > +#define   HWSTATUS_RBSY_MASK(x)		(((x) & 0xff) << 8)
> > +#define   HWSTATUS_RBSY_VALUE(x)	(((x) & 0xff) << 0)
> > +
> > +struct tegra_nand {
> > +	void __iomem *regs;
> > +	struct clk *clk;
> > +	struct gpio_desc *wp_gpio;
> > +
> > +	struct nand_chip chip;
> > +	struct mtd_info mtd;
> > +	struct device *dev;
> > +
> > +	struct completion command_complete;
> > +	struct completion dma_complete;
> > +
> > +	dma_addr_t data_dma;
> > +	void *data_buf;
> > +	dma_addr_t oob_dma;
> > +	void *oob_buf;
> > +
> > +	int cur_chip;
> > +};
> > +
> > +static inline struct tegra_nand *to_tegra_nand(struct mtd_info *mtd)
> > +{
> > +	return container_of(mtd, struct tegra_nand, mtd);
> > +}
> > +
> > +static struct nand_ecclayout tegra_nand_oob_16 = {
> > +	.eccbytes = 4,
> > +	.eccpos = { 4, 5, 6, 7 },
> > +	.oobfree = {
> > +		{ .offset = 8, . length = 8 }
> > +	}
> > +};
> > +
> > +static struct nand_ecclayout tegra_nand_oob_64 = {
> > +	.eccbytes = 36,
> > +	.eccpos = {
> > +		 4,  5,  6,  7,  8,  9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19,
> > +		20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35,
> > +		36, 37, 38, 39
> > +	},
> > +	.oobfree = {
> > +		{ .offset = 40, .length = 24 }
> > +	}
> > +};
> > +
> > +static struct nand_ecclayout tegra_nand_oob_128 = {
> > +	.eccbytes = 72,
> > +	.eccpos = {
> > +		 4,  5,  6,  7,  8,  9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19,
> > +		20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35,
> > +		36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51,
> > +		52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67,
> > +		68, 69, 70, 71, 72, 73, 74, 75
> > +	},
> > +	.oobfree = {
> > +		{ .offset = 76, .length = 52 }
> > +	}
> > +};
> > +
> > +static struct nand_ecclayout tegra_nand_oob_224 = {
> > +	.eccbytes = 144,
> > +	.eccpos = {
> > +		  4,   5,   6,   7,   8,   9,  10,  11,  12,  13,  14,  15,  16,
> > +		 17,  18,  19,  20,  21,  22,  23,  24,  25,  26,  27,  28,  29,
> > +		 30,  31,  32,  33,  34,  35,  36,  37,  38,  39,  40,  41,  42,
> > +		 43,  44,  45,  46,  47,  48,  49,  50,  51,  52,  53,  54,  55,
> > +		 56,  57,  58,  59,  60,  61,  62,  63,  64,  65,  66,  67,  68,
> > +		 69,  70,  71,  72,  73,  74,  75,  76,  77,  78,  79,  80,  81,
> > +		 82,  83,  84,  85,  86,  87,  88,  89,  90,  91,  92,  93,  94,
> > +		 95,  96,  97,  98,  99, 100, 101, 102, 103, 104, 105, 106, 107,
> > +		108, 109, 110, 111, 112, 113, 114, 115, 116, 117, 118, 119, 120,
> > +		121, 122, 123, 124, 125, 126, 127, 128, 129, 130, 131, 132, 133,
> > +		134, 135, 136, 137, 138, 139, 140, 141, 142, 143, 144, 145, 146,
> > +		147
> > +	},
> > +	.oobfree = {
> > +		{ .offset = 148, .length = 76 }
> > +	}
> > +};
> > +
> > +static irqreturn_t tegra_nand_irq(int irq, void *data)
> > +{
> > +	struct tegra_nand *nand = data;
> > +	u32 isr, dma;
> > +
> > +	isr = readl(nand->regs + ISR);
> > +	dma = readl(nand->regs + DMA_CTRL);
> > +
> > +	if (!isr && !(dma & DMA_CTRL_IS_DONE))
> > +		return IRQ_NONE;
> > +
> > +	if (isr & ISR_CMD_DONE)
> > +		complete(&nand->command_complete);
> > +
> > +	if (isr & ISR_UND)
> > +		dev_dbg(nand->dev, "FIFO underrun\n");
> > +
> > +	if (isr & ISR_OVR)
> > +		dev_dbg(nand->dev, "FIFO overrun\n");
> > +
> > +	/* handle DMA interrupts */
> > +	if (dma & DMA_CTRL_IS_DONE) {
> > +		writel(dma, nand->regs + DMA_CTRL);
> > +		complete(&nand->dma_complete);
> > +	}
> > +
> > +	/* clear interrupts */
> > +	writel(isr, nand->regs + ISR);
> > +
> > +	return IRQ_HANDLED;
> > +}
> > +
> > +static void tegra_nand_command(struct mtd_info *mtd, unsigned int command,
> > +			       int column, int page_addr)
> > +{
> > +	struct tegra_nand *nand = to_tegra_nand(mtd);
> > +	u32 value;
> > +
> > +	switch (command) {
> > +	case NAND_CMD_READOOB:
> > +		column += mtd->writesize;
> > +		/* fall-through */
> > +
> > +	case NAND_CMD_READ0:
> > +		writel(NAND_CMD_READ0, nand->regs + CMD_1);
> > +		writel(NAND_CMD_READSTART, nand->regs + CMD_2);
> > +
> > +		value = (page_addr << 16) | (column & 0xffff);
> > +		writel(value, nand->regs + ADDR_1);
> > +
> > +		value = page_addr >> 16;
> > +		writel(value, nand->regs + ADDR_2);
> > +
> > +		value = CMD_CLE | CMD_ALE | CMD_ALE_SIZE(4) | CMD_SEC_CMD |
> > +			CMD_RBSY_CHK | CMD_CE(nand->cur_chip) | CMD_GO;
> > +		writel(value, nand->regs + CMD);
> > +		break;
> > +
> > +	case NAND_CMD_SEQIN:
> > +		writel(NAND_CMD_SEQIN, nand->regs + CMD_1);
> > +
> > +		value = (page_addr << 16) | (column & 0xffff);
> > +		writel(value, nand->regs + ADDR_1);
> > +
> > +		value = page_addr >> 16;
> > +		writel(value, nand->regs + ADDR_2);
> > +
> > +		value = CMD_CLE | CMD_ALE | CMD_ALE_SIZE(4) |
> > +			CMD_CE(nand->cur_chip) | CMD_GO;
> > +		writel(value, nand->regs + CMD);
> > +		break;
> > +
> > +	case NAND_CMD_PAGEPROG:
> > +		writel(NAND_CMD_PAGEPROG, nand->regs + CMD_1);
> > +
> > +		value = CMD_CLE | CMD_CE(nand->cur_chip) | CMD_GO;
> > +		writel(value, nand->regs + CMD);
> > +		break;
> > +
> > +	case NAND_CMD_READID:
> > +		writel(NAND_CMD_READID, nand->regs + CMD_1);
> > +		writel(column & 0xff, nand->regs + ADDR_1);
> > +
> > +		value = CMD_GO | CMD_CLE | CMD_ALE | CMD_CE(nand->cur_chip);
> > +		writel(value, nand->regs + CMD);
> > +		break;
> > +
> > +	case NAND_CMD_ERASE1:
> > +		writel(NAND_CMD_ERASE1, nand->regs + CMD_1);
> > +		writel(NAND_CMD_ERASE2, nand->regs + CMD_2);
> > +		writel(page_addr, nand->regs + ADDR_1);
> > +
> > +		value = CMD_GO | CMD_CLE | CMD_ALE | CMD_ALE_SIZE(2) |
> > +			CMD_SEC_CMD | CMD_RBSY_CHK | CMD_CE(nand->cur_chip);
> > +		writel(value, nand->regs + CMD);
> > +		break;
> > +
> > +	case NAND_CMD_ERASE2:
> > +		return;
> > +
> > +	case NAND_CMD_STATUS:
> > +		writel(NAND_CMD_STATUS, nand->regs + CMD_1);
> > +
> > +		value = CMD_GO | CMD_CLE | CMD_CE(nand->cur_chip);
> > +		writel(value, nand->regs + CMD);
> > +		break;
> > +
> > +	case NAND_CMD_PARAM:
> > +		writel(NAND_CMD_PARAM, nand->regs + CMD_1);
> > +		writel(column & 0xff, nand->regs + ADDR_1);
> > +		value = CMD_GO | CMD_CLE | CMD_ALE | CMD_CE(nand->cur_chip);
> > +		writel(value, nand->regs + CMD);
> > +		break;
> > +
> > +	case NAND_CMD_RESET:
> > +		writel(NAND_CMD_RESET, nand->regs + CMD_1);
> > +
> > +		value = CMD_GO | CMD_CLE | CMD_CE(nand->cur_chip);
> > +		writel(value, nand->regs + CMD);
> > +		break;
> > +
> > +	default:
> > +		dev_warn(nand->dev, "unsupported command: %x\n", command);
> > +		return;
> > +	}
> > +
> > +	wait_for_completion(&nand->command_complete);
> > +}
> > +
> > +static void tegra_nand_select_chip(struct mtd_info *mtd, int chip)
> > +{
> > +	struct tegra_nand *nand = to_tegra_nand(mtd);
> > +
> > +	nand->cur_chip = chip;
> > +}
> > +
> > +static uint8_t tegra_nand_read_byte(struct mtd_info *mtd)
> > +{
> > +	struct tegra_nand *nand = to_tegra_nand(mtd);
> > +	u32 value;
> > +
> > +	value = CMD_TRANS_SIZE(0) | CMD_CE(nand->cur_chip) |
> > +		CMD_PIO | CMD_RX | CMD_A_VALID | CMD_GO;
> > +
> > +	writel(value, nand->regs + CMD);
> > +	wait_for_completion(&nand->command_complete);
> > +
> > +	return readl(nand->regs + RESP) & 0xff;
> > +}
> > +
> > +static void tegra_nand_read_buf(struct mtd_info *mtd, uint8_t *buffer,
> > +				int length)
> > +{
> > +	struct tegra_nand *nand = to_tegra_nand(mtd);
> > +	size_t i;
> > +
> > +	for (i = 0; i < length; i += 4) {
> > +		u32 value;
> > +		size_t n = min_t(size_t, length - i, 4);
> > +
> > +		value = CMD_GO | CMD_PIO | CMD_RX | CMD_A_VALID |
> > +			CMD_CE(nand->cur_chip) | CMD_TRANS_SIZE(n - 1);
> > +
> > +		writel(value, nand->regs + CMD);
> > +		wait_for_completion(&nand->command_complete);
> > +
> > +		value = readl(nand->regs + RESP);
> > +		memcpy(buffer + i, &value, n);
> > +	}
> > +}
> > +
> > +static void tegra_nand_write_buf(struct mtd_info *mtd, const uint8_t *buffer,
> > +				 int length)
> > +{
> > +	struct tegra_nand *nand = to_tegra_nand(mtd);
> > +	size_t i;
> > +
> > +	for (i = 0; i < length; i += 4) {
> > +		u32 value;
> > +		size_t n = min_t(size_t, length - i, 4);
> > +
> > +		memcpy(&value, buffer + i, n);
> > +		writel(value, nand->regs + RESP);
> > +
> > +		value = CMD_GO | CMD_PIO | CMD_TX | CMD_A_VALID |
> > +			CMD_CE(nand->cur_chip) | CMD_TRANS_SIZE(n - 1);
> > +
> > +		writel(value, nand->regs + CMD);
> > +		wait_for_completion(&nand->command_complete);
> > +	}
> > +}
> > +
> > +static int tegra_nand_read_page(struct mtd_info *mtd, struct nand_chip *chip,
> > +				uint8_t *buf, int oob_required, int page)
> > +{
> > +	struct tegra_nand *nand = to_tegra_nand(mtd);
> > +	u32 value;
> > +
> > +	value = readl(nand->regs + CFG);
> > +	value |= CFG_HW_ECC | CFG_ERR_COR;
> > +	writel(value, nand->regs + CFG);
> > +
> > +	writel(mtd->writesize - 1, nand->regs + DMA_CFG_A);
> > +	writel(nand->data_dma, nand->regs + DATA_PTR);
> > +
> > +	if (oob_required) {
> > +		writel(mtd->oobsize - 1, nand->regs + DMA_CFG_B);
> > +		writel(nand->oob_dma, nand->regs + TAG_PTR);
> > +	} else {
> > +		writel(0, nand->regs + DMA_CFG_B);
> > +		writel(0, nand->regs + TAG_PTR);
> > +	}
> > +
> > +	value = DMA_CTRL_GO | DMA_CTRL_IN | DMA_CTRL_PERF_EN |
> > +		DMA_CTRL_REUSE | DMA_CTRL_IE_DONE | DMA_CTRL_IS_DONE |
> > +		DMA_CTRL_BURST_8 | DMA_CTRL_EN_A;
> > +
> > +	if (oob_required)
> > +		value |= DMA_CTRL_EN_B;
> > +
> > +	writel(value, nand->regs + DMA_CTRL);
> > +
> > +	value = CMD_GO | CMD_RX | CMD_TRANS_SIZE(8) |
> > +		CMD_A_VALID | CMD_CE(nand->cur_chip);
> > +	if (oob_required)
> > +		value |= CMD_B_VALID;
> > +	writel(value, nand->regs + CMD);
> > +
> > +	wait_for_completion(&nand->command_complete);
> > +	wait_for_completion(&nand->dma_complete);
> > +
> > +	if (oob_required)
> > +		memcpy(chip->oob_poi, nand->oob_buf, mtd->oobsize);
> > +	memcpy(buf, nand->data_buf, mtd->writesize);
> > +
> > +	value = readl(nand->regs + CFG);
> > +	value &= ~(CFG_HW_ECC | CFG_ERR_COR);
> > +	writel(value, nand->regs + CFG);
> > +
> > +	value = readl(nand->regs + DEC_STATUS);
> > +
> > +	if (value & DEC_STATUS_A_ECC_FAIL) {
> > +		/*
> > +		 * The ECC isn't smart enough to figure out if a page is
> > +		 * completely erased and flags an error in this case. So we
> > +		 * check the read data here to figure out if it's a legitimate
> > +		 * error or a false positive.
> > +		 */
> > +		int i;
> > +		u32 *data = (u32 *)buf;
> > +		for (i = 0; i < mtd->writesize / 4; i++) {
> > +			if (data[i] != 0xffffffff) {
> > +				mtd->ecc_stats.failed++;
> > +				return -EBADMSG;
> > +			}
> > +		}
> 
> Hmm, what about OOB? It's possible to actually write 0xff to the entire
> page. This hunk means that such a data pattern would then be
> unprotected. You should probably check that *both* the main and OOB data
> are all 0xff; if there are non-0xff bytes, then that (probably, see the
> following) means someone intentionally wrote all 0xff to the page. [1]
> 

This check is only executed if the ECC engine flagged a non-correctable
error. If someone wrote all 0xff to the page there will be a proper ECC
checksum calculated and we won't get into this path. So to get this
check to wrongly paper over a legitimate error someone would need to
write almost all 0xff with a few bits 0, which then flip to a 1
afterwards, which is highly unlikely as far as I understand flash
technology.

> Also, your check doesn't handle the case of finding bitflips in erased
> pages. So not only do you need to check for all 0xff, but you also need
> to tolerate a few flips. e.g., using hweight*() functions. There is
> plenty of discussion on this subject, as many people have tried to
> resolve this for their various drivers. But none have really done this
> in a thorough and correct way, so few have been merged. Thus, I'd really
> like to get something like this merged to nand_base.c, with a NAND_*
> flag or two to enable it. That would help drivers like yours to easily
> grab a good (albeit, likely slow) implementation.
> 
Did those discussion lead somewhere? It seems they got stuck some time
ago. I'm all for using common infrastructure that does the right thing,
but I wouldn't like to base this driver on top of future work with no
clear roadmap.

> So, I'd like to see the first request (about OOB checks) solved, and if
> the larger bitflips-in-erased-pages issue isn't addressed, please
> include a FIXME comment, or something similar.
> 
> > +		return 0;
> > +	}
> > +
> > +	if (value & DEC_STATUS_ERR_COUNT_MASK) {
> > +		value = (value & DEC_STATUS_ERR_COUNT_MASK) >>
> > +			DEC_STATUS_ERR_COUNT_SHIFT;
> 
> What does this ERR_COUNT represent? The total bitflips seen in this
> page? The max seen per ECC region? Or something else?
> 
> > +		mtd->ecc_stats.corrected += value;
> 
> I ask because this ^^^ should be accounting the total bitflips for the
> page, if possible...
> 
> > +		return value;
> 
> ...and this ^^^ should be returning the max bitflips seen in a single
> correction region (see the mtd_read() API). There is a subtle
> difference.
> 
Urgh, yeah. The value is bitflips per page. I think there is another
register that should give max errors per ECC region, but I'm not sure it
works correctly. Will test that. Thanks for the hint.

> > +	}
> > +
> > +	return 0;
> > +}
> > +
> > +static int tegra_nand_write_page(struct mtd_info *mtd, struct nand_chip *chip,
> > +				 const uint8_t *buf, int oob_required)
> > +{
> > +	struct tegra_nand *nand = to_tegra_nand(mtd);
> > +	unsigned long value;
> > +
> > +	value = readl(nand->regs + CFG);
> > +	value |= CFG_HW_ECC | CFG_ERR_COR;
> > +	writel(value, nand->regs + CFG);
> > +
> > +	memcpy(nand->data_buf, buf, mtd->writesize);
> > +
> > +	writel(mtd->writesize - 1, nand->regs + DMA_CFG_A);
> > +	writel(nand->data_dma, nand->regs + DATA_PTR);
> > +
> > +	writel(0, nand->regs + DMA_CFG_B);
> > +	writel(0, nand->regs + TAG_PTR);
> > +
> > +	value = DMA_CTRL_GO | DMA_CTRL_OUT | DMA_CTRL_PERF_EN |
> > +		DMA_CTRL_IE_DONE | DMA_CTRL_IS_DONE |
> > +		DMA_CTRL_BURST_8 | DMA_CTRL_EN_A;
> > +	writel(value, nand->regs + DMA_CTRL);
> > +
> > +	value = CMD_GO | CMD_TX | CMD_A_VALID | CMD_TRANS_SIZE(8) |
> > +		CMD_CE(nand->cur_chip);
> > +	writel(value, nand->regs + CMD);
> > +
> > +	wait_for_completion(&nand->command_complete);
> > +	wait_for_completion(&nand->dma_complete);
> > +
> > +	value = readl(nand->regs + CFG);
> > +	value &= ~(CFG_HW_ECC | CFG_ERR_COR);
> > +	writel(value, nand->regs + CFG);
> > +
> > +	return 0;
> > +}
> > +
> > +static void tegra_nand_setup_timing(struct tegra_nand *nand, int mode)
> > +{
> 
> This function could use some comments. The math can be easy to get
> wrong, especially without the annotation of units (e.g., picoseconds).
> Also, look out for rounding inaccuracies. DIV_ROUND_UP() is nice for
> getting conservative conversions at times.
> 
The timing formulas are listed in the TRM and I don't think it makes
sense to repeat them here. Are you okay with a pointer to the relevant
section in the TRM?

> > +	unsigned long rate = clk_get_rate(nand->clk) / 1000000;
> > +	unsigned long period = 1000000 / rate;
> > +	const struct nand_sdr_timings *timings;
> > +	u32 val, reg = 0;
> > +
> > +	timings = onfi_async_timing_mode_to_sdr_timings(mode);
> > +
> > +	val = max3(timings->tAR_min, timings->tRR_min,
> > +		   timings->tRC_min) / period;
> > +	if (val > 2)
> > +		val -= 3;
> > +	reg |= TIMING_TCR_TAR_TRR(val);
> > +
> > +	val = max(max(timings->tCS_min, timings->tCH_min),
> > +		  max(timings->tALS_min, timings->tALH_min)) / period;
> > +	if (val > 1)
> > +		val -= 2;
> > +	reg |= TIMING_TCS(val);
> > +
> > +	val = (max(timings->tRP_min, timings->tREA_max) + 6000) / period;
> > +	reg |= (TIMING_TRP(val) | TIMING_TRP_RESP(val));
> > +
> > +	reg |= TIMING_TWB(timings->tWB_max / period);
> > +	reg |= TIMING_TWHR(timings->tWHR_min / period);
> > +	reg |= TIMING_TWH(timings->tWH_min / period);
> > +	reg |= TIMING_TWP(timings->tWP_min / period);
> > +	reg |= TIMING_TRH(timings->tRHW_min / period);
> > +
> > +	writel(reg, nand->regs + TIMING_1);
> > +
> > +	val = timings->tADL_min / period;
> > +	if (val > 2)
> > +		val -= 3;
> > +	reg = TIMING_TADL(val);
> > +
> > +	writel(reg, nand->regs + TIMING_2);
> > +}
> > +
> > +static void tegra_nand_setup_chiptiming(struct tegra_nand *nand)
> > +{
> > +	struct nand_chip *chip = &nand->chip;
> > +	int mode;
> > +
> > +	mode = onfi_get_async_timing_mode(chip);
> > +	if (mode == ONFI_TIMING_MODE_UNKNOWN)
> > +		mode = chip->onfi_timing_mode_default;
> > +	else
> > +		mode = fls(mode);
> > +
> > +	tegra_nand_setup_timing(nand, mode);
> > +}
> > +
> > +static int tegra_nand_probe(struct platform_device *pdev)
> > +{
> > +	struct reset_control *rst;
> > +	struct tegra_nand *nand;
> > +	struct nand_chip *chip;
> > +	struct mtd_info *mtd;
> > +	struct resource *res;
> > +	unsigned long value;
> > +	int irq, buswidth, err = 0;
> > +
> > +	nand = devm_kzalloc(&pdev->dev, sizeof(*nand), GFP_KERNEL);
> > +	if (!nand)
> > +		return -ENOMEM;
> > +
> > +	nand->dev = &pdev->dev;
> > +
> > +	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
> > +	nand->regs = devm_ioremap_resource(&pdev->dev, res);
> > +	if (IS_ERR(nand->regs))
> > +		return PTR_ERR(nand->regs);
> > +
> > +	irq = platform_get_irq(pdev, 0);
> > +	err = devm_request_irq(&pdev->dev, irq, tegra_nand_irq, 0,
> > +			       dev_name(&pdev->dev), nand);
> > +	if (err)
> > +		return err;
> > +
> > +	rst = devm_reset_control_get(&pdev->dev, "nand");
> > +	if (IS_ERR(rst))
> > +		return PTR_ERR(rst);
> > +
> > +	nand->clk = devm_clk_get(&pdev->dev, "nand");
> > +	if (IS_ERR(nand->clk))
> > +		return PTR_ERR(nand->clk);
> > +
> > +	nand->wp_gpio = gpiod_get_optional(&pdev->dev, "nvidia,wp-gpios",
> > +					   GPIOD_OUT_HIGH);
> > +	if (IS_ERR(nand->wp_gpio))
> > +		return PTR_ERR(nand->wp_gpio);
> > +
> > +	buswidth = of_get_nand_bus_width(pdev->dev.of_node);
> > +	if (buswidth < 0)
> > +		return buswidth;
> 
> You could set chip->dn, then nand_dt_init() might capture this for you.
> 
Thanks, will do.

> > +
> > +	err = clk_prepare_enable(nand->clk);
> > +	if (err)
> > +		return err;
> > +
> > +	reset_control_assert(rst);
> > +	udelay(2);
> > +	reset_control_deassert(rst);
> > +
> > +	value = HWSTATUS_RDSTATUS_MASK(1) | HWSTATUS_RDSTATUS_VALUE(0) |
> > +		HWSTATUS_RBSY_MASK(NAND_STATUS_READY) |
> > +		HWSTATUS_RBSY_VALUE(NAND_STATUS_READY);
> > +	writel(NAND_CMD_STATUS, nand->regs + HWSTATUS_CMD);
> > +	writel(value, nand->regs + HWSTATUS_MASK);
> > +
> > +	init_completion(&nand->command_complete);
> > +	init_completion(&nand->dma_complete);
> > +
> > +	mtd = &nand->mtd;
> > +	mtd->name = "tegra_nand";
> > +	mtd->owner = THIS_MODULE;
> > +	mtd->priv = &nand->chip;
> > +
> > +	/* clear interrupts */
> > +	value = readl(nand->regs + ISR);
> > +	writel(value, nand->regs + ISR);
> > +
> > +	writel(DMA_CTRL_IS_DONE, nand->regs + DMA_CTRL);
> > +
> > +	/* enable interrupts */
> > +	value = IER_UND | IER_OVR | IER_CMD_DONE | IER_ECC_ERR | IER_GIE;
> > +	writel(value, nand->regs + IER);
> > +
> > +	value = 0;
> > +	if (buswidth == 16)
> > +		value |= CFG_BUS_WIDTH_16;
> > +	writel(value, nand->regs + CFG);
> > +
> > +	chip = &nand->chip;
> > +	chip->options = NAND_NO_SUBPAGE_WRITE;
> > +	chip->cmdfunc = tegra_nand_command;
> > +	chip->select_chip = tegra_nand_select_chip;
> > +	chip->read_byte = tegra_nand_read_byte;
> > +	chip->read_buf = tegra_nand_read_buf;
> > +	chip->write_buf = tegra_nand_write_buf;
> > +
> > +	if (of_get_nand_on_flash_bbt(pdev->dev.of_node))
> > +		chip->bbt_options = NAND_BBT_USE_FLASH | NAND_BBT_NO_OOB;
> 
> Again, nand_dt_init() might help you. You might then augment it with:
> 
> 	if (chip->bbt_options & NAND_BBT_USE_FLASH)
> 		chip->bbt_options |= NAND_BBT_NO_OOB;
> 
> > +
> > +	tegra_nand_setup_timing(nand, 0);
> > +
> > +	err = nand_scan_ident(mtd, 1, NULL);
> > +	if (err)
> > +		return err;
> > +
> > +	nand->data_buf = dmam_alloc_coherent(&pdev->dev, mtd->writesize,
> > +					    &nand->data_dma, GFP_KERNEL);
> > +	if (!nand->data_buf)
> > +		return -ENOMEM;
> > +
> > +	nand->oob_buf = dmam_alloc_coherent(&pdev->dev, mtd->oobsize,
> > +					    &nand->oob_dma, GFP_KERNEL);
> > +	if (!nand->oob_buf)
> > +		return -ENOMEM;
> > +
> > +	chip->ecc.mode = NAND_ECC_HW;
> > +	chip->ecc.size = 512;
> > +	chip->ecc.bytes = mtd->oobsize;
> > +	chip->ecc.read_page = tegra_nand_read_page;
> > +	chip->ecc.write_page = tegra_nand_write_page;
> > +
> > +	value = readl(nand->regs + CFG);
> > +	value |=  CFG_PIPE_EN | CFG_SKIP_SPARE | CFG_SKIP_SPARE_SIZE_4;
> > +
> > +	switch (mtd->oobsize) {
> > +	case 16:
> > +		chip->ecc.layout = &tegra_nand_oob_16;
> > +		chip->ecc.strength = 1;
> > +		value |= CFG_TAG_BYTE_SIZE(tegra_nand_oob_16.oobfree[0].length
> > +			 - 1);
> > +		break;
> > +	case 64:
> > +		chip->ecc.layout = &tegra_nand_oob_64;
> > +		chip->ecc.strength = 8;
> > +		value |= CFG_ECC_SEL | CFG_TVAL_8 |
> > +			 CFG_TAG_BYTE_SIZE(tegra_nand_oob_64.oobfree[0].length
> > +			 - 1);
> > +		break;
> > +	case 128:
> > +		chip->ecc.layout = &tegra_nand_oob_128;
> > +		chip->ecc.strength = 8;
> > +		value |= CFG_ECC_SEL | CFG_TVAL_8 |
> > +			 CFG_TAG_BYTE_SIZE(tegra_nand_oob_128.oobfree[0].length
> > +			 - 1);
> > +		break;
> > +	case 224:
> > +		chip->ecc.layout = &tegra_nand_oob_224;
> > +		chip->ecc.strength = 8;
> > +		value |= CFG_ECC_SEL | CFG_TVAL_8 |
> > +			 CFG_TAG_BYTE_SIZE(tegra_nand_oob_224.oobfree[0].length
> > +			 - 1);
> > +		break;
> > +	default:
> > +		dev_err(&pdev->dev, "unhandled OOB size %d\n", mtd->oobsize);
> > +		return -ENODEV;
> > +	}
> > +
> > +	switch (mtd->writesize) {
> > +	case 256:
> > +		value |= CFG_PS_256;
> > +		break;
> > +	case 512:
> > +		value |= CFG_PS_512;
> > +		break;
> > +	case 1024:
> > +		value |= CFG_PS_1024;
> > +		break;
> > +	case 2048:
> > +		value |= CFG_PS_2048;
> > +		break;
> > +	case 4096:
> > +		value |= CFG_PS_4096;
> > +		break;
> > +	default:
> > +		dev_err(&pdev->dev, "unhandled writesize %d\n", mtd->writesize);
> > +		return -ENODEV;
> > +	}
> > +
> > +	writel(value, nand->regs + CFG);
> > +
> > +	tegra_nand_setup_chiptiming(nand);
> > +
> > +	err = nand_scan_tail(mtd);
> > +	if (err)
> > +		return err;
> > +
> > +	mtd_device_parse_register(mtd, NULL,
> > +				  &(struct mtd_part_parser_data) {
> > +					.of_node = pdev->dev.of_node,
> > +				  },
> > +				  NULL, 0);
> 
> Check the return value for errors.
> 
Will do,

Thanks,
Lucas


--
To unsubscribe from this list: send the line "unsubscribe linux-tegra" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html

Hi,

On Wed, Jul 22, 2015 at 10:42:40PM +0200, Lucas Stach wrote:
> Am Dienstag, den 21.07.2015, 14:27 -0700 schrieb Brian Norris:
> > On Sun, May 10, 2015 at 08:29:59PM +0200, Lucas Stach wrote:
> > > --- /dev/null
> > > +++ b/drivers/mtd/nand/tegra_nand.c
> > > @@ -0,0 +1,801 @@
...
> > > +static int tegra_nand_read_page(struct mtd_info *mtd, struct nand_chip *chip,
> > > +				uint8_t *buf, int oob_required, int page)
> > > +{
...
> > > +	value = readl(nand->regs + DEC_STATUS);
> > > +
> > > +	if (value & DEC_STATUS_A_ECC_FAIL) {
> > > +		/*
> > > +		 * The ECC isn't smart enough to figure out if a page is
> > > +		 * completely erased and flags an error in this case. So we
> > > +		 * check the read data here to figure out if it's a legitimate
> > > +		 * error or a false positive.
> > > +		 */
> > > +		int i;
> > > +		u32 *data = (u32 *)buf;
> > > +		for (i = 0; i < mtd->writesize / 4; i++) {
> > > +			if (data[i] != 0xffffffff) {
> > > +				mtd->ecc_stats.failed++;
> > > +				return -EBADMSG;
> > > +			}
> > > +		}
> > 
> > Hmm, what about OOB? It's possible to actually write 0xff to the entire
> > page. This hunk means that such a data pattern would then be
> > unprotected. You should probably check that *both* the main and OOB data
> > are all 0xff; if there are non-0xff bytes, then that (probably, see the
> > following) means someone intentionally wrote all 0xff to the page. [1]
> > 
> 
> This check is only executed if the ECC engine flagged a non-correctable
> error. If someone wrote all 0xff to the page there will be a proper ECC
> checksum calculated and we won't get into this path. So to get this
> check to wrongly paper over a legitimate error someone would need to
> write almost all 0xff with a few bits 0, which then flip to a 1
> afterwards, which is highly unlikely as far as I understand flash
> technology.

On second thought, the case I mentioned is not a problem for you
currently. You'll just have more problems once you start seeing bitflips
in erased pages.

And I agree, the latter case you mention is probably pretty unlikely,
though I'm not really an EE expert to tell you cannot see such a 0->1
"stuck bit".

But anyway, why don't you check the spare area too? It turns the
"unlikely" problem into a non-issue.

At the same time, I see that you don't support raw page reads/writes. Is
it impossible? Or is it just an oversight?

> > Also, your check doesn't handle the case of finding bitflips in erased
> > pages. So not only do you need to check for all 0xff, but you also need
> > to tolerate a few flips. e.g., using hweight*() functions. There is
> > plenty of discussion on this subject, as many people have tried to
> > resolve this for their various drivers. But none have really done this
> > in a thorough and correct way, so few have been merged. Thus, I'd really
> > like to get something like this merged to nand_base.c, with a NAND_*
> > flag or two to enable it. That would help drivers like yours to easily
> > grab a good (albeit, likely slow) implementation.
> > 
> Did those discussion lead somewhere? It seems they got stuck some time
> ago. I'm all for using common infrastructure that does the right thing,
> but I wouldn't like to base this driver on top of future work with no
> clear roadmap.

That was really just an FYI. No, the discussion didn't lead much of
anywhere. A bunch of half-assed implementations, and me with no time
(and even less hardware, now).

> > So, I'd like to see the first request (about OOB checks) solved, and if
> > the larger bitflips-in-erased-pages issue isn't addressed, please
> > include a FIXME comment, or something similar.

I'd still either like to see a good reason not to check the OOB for
oob[:] == 0xffffffff, or else fix that up. The rest (which is, like you
say, "bas[ing] this driver on top of future work") is not your problem
ATM [1].

...
> > > +static void tegra_nand_setup_timing(struct tegra_nand *nand, int mode)
> > > +{
> > 
> > This function could use some comments. The math can be easy to get
> > wrong, especially without the annotation of units (e.g., picoseconds).
> > Also, look out for rounding inaccuracies. DIV_ROUND_UP() is nice for
> > getting conservative conversions at times.
> > 
> The timing formulas are listed in the TRM and I don't think it makes
> sense to repeat them here. Are you okay with a pointer to the relevant
> section in the TRM?

I don't think we need to see all the formulas again, but a TRM reference
could be nice. I was asking mostly about units, and also about the
round-down division. I'll add a few more comments below.

> > > +	unsigned long rate = clk_get_rate(nand->clk) / 1000000;

^^ conversion to MHz? Why? (comment) How about DIV_ROUND_UP, so you
don't overestimate the clock period (and thus underestimate the number
of clock periods needed)?

> > > +	unsigned long period = 1000000 / rate;

And period is... in picoseconds? It took me a minute to figure that out
for sure, so IMO it deserves a comment.

> > > +	const struct nand_sdr_timings *timings;
> > > +	u32 val, reg = 0;
> > > +
> > > +	timings = onfi_async_timing_mode_to_sdr_timings(mode);
> > > +
> > > +	val = max3(timings->tAR_min, timings->tRR_min,
> > > +		   timings->tRC_min) / period;

DIV_ROUND_UP()? You don't want to lop off a partial timing cycle, right?
Simliar comments apply throughout. Or please correct me if I'm wrong.

> > > +	if (val > 2)
> > > +		val -= 3;
> > > +	reg |= TIMING_TCR_TAR_TRR(val);
> > > +
> > > +	val = max(max(timings->tCS_min, timings->tCH_min),
> > > +		  max(timings->tALS_min, timings->tALH_min)) / period;
> > > +	if (val > 1)
> > > +		val -= 2;
> > > +	reg |= TIMING_TCS(val);
> > > +
> > > +	val = (max(timings->tRP_min, timings->tREA_max) + 6000) / period;
> > > +	reg |= (TIMING_TRP(val) | TIMING_TRP_RESP(val));
> > > +
> > > +	reg |= TIMING_TWB(timings->tWB_max / period);
> > > +	reg |= TIMING_TWHR(timings->tWHR_min / period);
> > > +	reg |= TIMING_TWH(timings->tWH_min / period);
> > > +	reg |= TIMING_TWP(timings->tWP_min / period);
> > > +	reg |= TIMING_TRH(timings->tRHW_min / period);
> > > +
> > > +	writel(reg, nand->regs + TIMING_1);
> > > +
> > > +	val = timings->tADL_min / period;
> > > +	if (val > 2)
> > > +		val -= 3;
> > > +	reg = TIMING_TADL(val);
> > > +
> > > +	writel(reg, nand->regs + TIMING_2);
> > > +}

Brian

[1] Unless, of course, you start using NAND flash that sees bitflips in
    erased pages.
--
To unsubscribe from this list: send the line "unsubscribe linux-tegra" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html

Hi Brian,

a bit of investigation later I have some coherent answers to your
requests. :)

Am Mittwoch, den 22.07.2015, 16:10 -0700 schrieb Brian Norris:
> Hi,
> 
> On Wed, Jul 22, 2015 at 10:42:40PM +0200, Lucas Stach wrote:
> > Am Dienstag, den 21.07.2015, 14:27 -0700 schrieb Brian Norris:
> > > On Sun, May 10, 2015 at 08:29:59PM +0200, Lucas Stach wrote:
> > > > --- /dev/null
> > > > +++ b/drivers/mtd/nand/tegra_nand.c
> > > > @@ -0,0 +1,801 @@
> ...
> > > > +static int tegra_nand_read_page(struct mtd_info *mtd, struct nand_chip *chip,
> > > > +				uint8_t *buf, int oob_required, int page)
> > > > +{
> ...
> > > > +	value = readl(nand->regs + DEC_STATUS);
> > > > +
> > > > +	if (value & DEC_STATUS_A_ECC_FAIL) {
> > > > +		/*
> > > > +		 * The ECC isn't smart enough to figure out if a page is
> > > > +		 * completely erased and flags an error in this case. So we
> > > > +		 * check the read data here to figure out if it's a legitimate
> > > > +		 * error or a false positive.
> > > > +		 */
> > > > +		int i;
> > > > +		u32 *data = (u32 *)buf;
> > > > +		for (i = 0; i < mtd->writesize / 4; i++) {
> > > > +			if (data[i] != 0xffffffff) {
> > > > +				mtd->ecc_stats.failed++;
> > > > +				return -EBADMSG;
> > > > +			}
> > > > +		}
> > > 
> > > Hmm, what about OOB? It's possible to actually write 0xff to the entire
> > > page. This hunk means that such a data pattern would then be
> > > unprotected. You should probably check that *both* the main and OOB data
> > > are all 0xff; if there are non-0xff bytes, then that (probably, see the
> > > following) means someone intentionally wrote all 0xff to the page. [1]
> > > 
> > 
> > This check is only executed if the ECC engine flagged a non-correctable
> > error. If someone wrote all 0xff to the page there will be a proper ECC
> > checksum calculated and we won't get into this path. So to get this
> > check to wrongly paper over a legitimate error someone would need to
> > write almost all 0xff with a few bits 0, which then flip to a 1
> > afterwards, which is highly unlikely as far as I understand flash
> > technology.
> 
> On second thought, the case I mentioned is not a problem for you
> currently. You'll just have more problems once you start seeing bitflips
> in erased pages.
> 
> And I agree, the latter case you mention is probably pretty unlikely,
> though I'm not really an EE expert to tell you cannot see such a 0->1
> "stuck bit".
> 
> But anyway, why don't you check the spare area too? It turns the
> "unlikely" problem into a non-issue.
> 
If I'm using the HWECC/DMA functions I have no way to check the OOB ECC
area. The controller just skips over it and only transfers user
available OOB data into the buffer. So checking the OOB is unfortunately
not easily done.

> At the same time, I see that you don't support raw page reads/writes. Is
> it impossible? Or is it just an oversight?
> 
It's possible, but I've skipped it for now, as this would increase the
amount of testing I have to do to validate each round of those patches
even more and I don't see much benefit right now. So this remains a
TODO.

[...]
> > > > +	unsigned long rate = clk_get_rate(nand->clk) / 1000000;
> 
> ^^ conversion to MHz? Why? (comment) How about DIV_ROUND_UP, so you
> don't overestimate the clock period (and thus underestimate the number
> of clock periods needed)?
> 
> > > > +	unsigned long period = 1000000 / rate;
> 
> And period is... in picoseconds? It took me a minute to figure that out
> for sure, so IMO it deserves a comment.
> 
> > > > +	const struct nand_sdr_timings *timings;
> > > > +	u32 val, reg = 0;
> > > > +
> > > > +	timings = onfi_async_timing_mode_to_sdr_timings(mode);
> > > > +
> > > > +	val = max3(timings->tAR_min, timings->tRR_min,
> > > > +		   timings->tRC_min) / period;
> 
> DIV_ROUND_UP()? You don't want to lop off a partial timing cycle, right?
> Simliar comments apply throughout. Or please correct me if I'm wrong.
> 

I agree with the reasoning here and made those changes for v4.

> > > > +	if (val > 2)
> > > > +		val -= 3;
> > > > +	reg |= TIMING_TCR_TAR_TRR(val);
> > > > +
> > > > +	val = max(max(timings->tCS_min, timings->tCH_min),
> > > > +		  max(timings->tALS_min, timings->tALH_min)) / period;
> > > > +	if (val > 1)
> > > > +		val -= 2;
> > > > +	reg |= TIMING_TCS(val);
> > > > +
> > > > +	val = (max(timings->tRP_min, timings->tREA_max) + 6000) / period;
> > > > +	reg |= (TIMING_TRP(val) | TIMING_TRP_RESP(val));
> > > > +
> > > > +	reg |= TIMING_TWB(timings->tWB_max / period);
> > > > +	reg |= TIMING_TWHR(timings->tWHR_min / period);
> > > > +	reg |= TIMING_TWH(timings->tWH_min / period);
> > > > +	reg |= TIMING_TWP(timings->tWP_min / period);
> > > > +	reg |= TIMING_TRH(timings->tRHW_min / period);
> > > > +
> > > > +	writel(reg, nand->regs + TIMING_1);
> > > > +
> > > > +	val = timings->tADL_min / period;
> > > > +	if (val > 2)
> > > > +		val -= 3;
> > > > +	reg = TIMING_TADL(val);
> > > > +
> > > > +	writel(reg, nand->regs + TIMING_2);
> > > > +}
> 
Regards,
Lucas

--
To unsubscribe from this list: send the line "unsubscribe linux-tegra" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html

Am Dienstag, den 21.07.2015, 14:27 -0700 schrieb Brian Norris:

[...]
> 
> > +		return 0;
> > +	}
> > +
> > +	if (value & DEC_STATUS_ERR_COUNT_MASK) {
> > +		value = (value & DEC_STATUS_ERR_COUNT_MASK) >>
> > +			DEC_STATUS_ERR_COUNT_SHIFT;
> 
> What does this ERR_COUNT represent? The total bitflips seen in this
> page? The max seen per ECC region? Or something else?
> 
> > +		mtd->ecc_stats.corrected += value;
> 
> I ask because this ^^^ should be accounting the total bitflips for the
> page, if possible...
> 
> > +		return value;
> 
> ...and this ^^^ should be returning the max bitflips seen in a single
> correction region (see the mtd_read() API). There is a subtle
> difference.
> 
I've checked this again and unfortunately the DEC_STATUS_ERR_COUNT seems
to be completely bogus. It is certainly only set when there are
bitflips, but it doesn't represent a valid value.

I have another register that seems to accurately reflect the maximum
number of bitflips in any of the 512b ECC blocks, so I'm able to return
the correct amount of bitflips to the upper level.
The downside is that the hardware already does the calculation of max
bitflips, so I'm unable to count bitflips correctly for the stats. All I
can do is to return a pessimistic value that assumes that all 512b
blocks had the returned number of bitflips. Could this be a problem?

Regards,
Lucas



--
To unsubscribe from this list: send the line "unsubscribe linux-tegra" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html

On Mon, Jul 27, 2015 at 09:19:57PM +0200, Lucas Stach wrote:
> Am Dienstag, den 21.07.2015, 14:27 -0700 schrieb Brian Norris:
> I've checked this again and unfortunately the DEC_STATUS_ERR_COUNT seems
> to be completely bogus. It is certainly only set when there are
> bitflips, but it doesn't represent a valid value.

:( HW sucks.

> I have another register that seems to accurately reflect the maximum
> number of bitflips in any of the 512b ECC blocks, so I'm able to return
> the correct amount of bitflips to the upper level.
> The downside is that the hardware already does the calculation of max
> bitflips, so I'm unable to count bitflips correctly for the stats. All I
> can do is to return a pessimistic value that assumes that all 512b
> blocks had the returned number of bitflips. Could this be a problem?

As things currently stand: no, I don't think so. The ecc_stats are
actually mostly just that -- statistics. Some pieces of the codebase use
the fact they increased as a sign, but they don't care about the actual
number. The max_bitflips calculation, however, is very important so that
MTD can determine whether we've reached the reliability threshold.

So I guess you have some flexibility in how to report this, but I think
two main options are sane:

 1. leave as-is; you can only guarantee that max_bitflips occurred in
 total, so only increment ecc_stats.corrected by max_bitflips

 2. change to

     ecc_stats.corrected += max_bitflips * chip->ecc.steps;

 This is the maximum that might have occured on this page read.

IOW, option 1 is optimistic and option 2 is pessimistic. Either way,
this probably deserves a comment in the code.

Regards,
Brian
--
To unsubscribe from this list: send the line "unsubscribe linux-tegra" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html