[v6,11/11] pwm: Add Raspberry Pi Firmware based PWM bus

Adds support to control the PWM bus available in official Raspberry Pi
PoE HAT. Only RPi's co-processor has access to it, so commands have to
be sent through RPi's firmware mailbox interface.

Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
---

Changes since v3:
 - Rename compatible string to be more explicit WRT to bus's limitations

Changes since v2:
 - Use devm_rpi_firmware_get()
 - Rename driver
 - Small cleanups

Changes since v1:
 - Use default pwm bindings and get rid of xlate() function
 - Correct spelling errors
 - Correct apply() function
 - Round values
 - Fix divisions in arm32 mode
 - Small cleanups

 drivers/pwm/Kconfig               |   9 ++
 drivers/pwm/Makefile              |   1 +
 drivers/pwm/pwm-raspberrypi-poe.c | 216 ++++++++++++++++++++++++++++++
 3 files changed, 226 insertions(+)
 create mode 100644 drivers/pwm/pwm-raspberrypi-poe.c

Hello Nicolas,

On Fri, Dec 11, 2020 at 05:48:00PM +0100, Nicolas Saenz Julienne wrote:
> diff --git a/drivers/pwm/pwm-raspberrypi-poe.c b/drivers/pwm/pwm-raspberrypi-poe.c
> new file mode 100644
> index 000000000000..24b498839fcc
> --- /dev/null
> +++ b/drivers/pwm/pwm-raspberrypi-poe.c
> @@ -0,0 +1,216 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright 2020 Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
> + * For more information on Raspberry Pi's PoE hat see:
> + * https://www.raspberrypi.org/products/poe-hat/
> + *
> + * Limitations:
> + *  - No disable bit, so a disabled PWM is simulated by duty_cycle 0
> + *  - Only normal polarity
> + *  - Fixed 12.5 kHz period
> + *
> + * The current period is completed when HW is reconfigured.
> + */
> +
> +#include <linux/module.h>
> +#include <linux/of.h>
> +#include <linux/platform_device.h>
> +#include <linux/pwm.h>
> +
> +#include <soc/bcm2835/raspberrypi-firmware.h>
> +#include <dt-bindings/pwm/raspberrypi,firmware-poe-pwm.h>
> +
> +#define RPI_PWM_MAX_DUTY		255
> +#define RPI_PWM_PERIOD_NS		80000 /* 12.5 kHz */
> +
> +#define RPI_PWM_CUR_DUTY_REG		0x0
> +#define RPI_PWM_DEF_DUTY_REG		0x1
> +
> +struct raspberrypi_pwm {
> +	struct rpi_firmware *firmware;
> +	struct pwm_chip chip;
> +	unsigned int duty_cycle;
> +};
> +
> +struct raspberrypi_pwm_prop {
> +	__le32 reg;
> +	__le32 val;
> +	__le32 ret;
> +} __packed;
> +
> +static inline struct raspberrypi_pwm *to_raspberrypi_pwm(struct pwm_chip *chip)

I'd like to see this function use the same prefix as the other
functions. I suggest "raspberrypi_pwm_from_chip".

> +{
> +	return container_of(chip, struct raspberrypi_pwm, chip);
> +}
> +
> +static int raspberrypi_pwm_set_property(struct rpi_firmware *firmware,
> +					u32 reg, u32 val)
> +{
> +	struct raspberrypi_pwm_prop msg = {
> +		.reg = cpu_to_le32(reg),
> +		.val = cpu_to_le32(val),
> +	};
> +	int ret;
> +
> +	ret = rpi_firmware_property(firmware, RPI_FIRMWARE_SET_POE_HAT_VAL,
> +				    &msg, sizeof(msg));
> +	if (ret)
> +		return ret;
> +	if (msg.ret)
> +		return -EIO;
> +
> +	return 0;
> +}
> +
> +static int raspberrypi_pwm_get_property(struct rpi_firmware *firmware,
> +					u32 reg, u32 *val)
> +{
> +	struct raspberrypi_pwm_prop msg = {
> +		.reg = reg
> +	};
> +	int ret;
> +
> +	ret = rpi_firmware_property(firmware, RPI_FIRMWARE_GET_POE_HAT_VAL,
> +				    &msg, sizeof(msg));
> +	if (ret)
> +		return ret;
> +	if (msg.ret)
> +		return -EIO;
> +
> +	*val = le32_to_cpu(msg.val);
> +
> +	return 0;
> +}
> +
> +static void raspberrypi_pwm_get_state(struct pwm_chip *chip,
> +				      struct pwm_device *pwm,
> +				      struct pwm_state *state)
> +{
> +	struct raspberrypi_pwm *rpipwm = to_raspberrypi_pwm(chip);
> +
> +	state->period = RPI_PWM_PERIOD_NS;
> +	state->duty_cycle = DIV_ROUND_CLOSEST(rpipwm->duty_cycle * RPI_PWM_PERIOD_NS,
> +					      RPI_PWM_MAX_DUTY);

Please round up here ...

> +	state->enabled = !!(rpipwm->duty_cycle);
> +	state->polarity = PWM_POLARITY_NORMAL;
> +}
> +
> +static int raspberrypi_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
> +			         const struct pwm_state *state)
> +{
> +	struct raspberrypi_pwm *rpipwm = to_raspberrypi_pwm(chip);
> +	unsigned int duty_cycle;
> +	int ret;
> +
> +        if (state->period < RPI_PWM_PERIOD_NS ||
> +            state->polarity != PWM_POLARITY_NORMAL)
> +                return -EINVAL;
> +
> +        if (!state->enabled)
> +                duty_cycle = 0;
> +        else if (state->duty_cycle < RPI_PWM_PERIOD_NS)
> +                duty_cycle = DIV_ROUND_CLOSEST_ULL(state->duty_cycle * RPI_PWM_MAX_DUTY,
> +					           RPI_PWM_PERIOD_NS);

... and round down here.

Just to be sure: writing RPI_PWM_MAX_DUTY (i.e. 255) yields 100% duty
cycle, right?

> +        else
> +                duty_cycle = RPI_PWM_MAX_DUTY;
> +
> +	if (duty_cycle == rpipwm->duty_cycle)
> +		return 0;
> +
> +	ret = raspberrypi_pwm_set_property(rpipwm->firmware, RPI_PWM_CUR_DUTY_REG,
> +					   duty_cycle);
> +	if (ret) {
> +		dev_err(chip->dev, "Failed to set duty cycle: %d\n", ret);
> +		return ret;
> +	}
> +
> +	/*
> +	 * This sets the default duty cycle after resetting the board, we
> +	 * updated it every time to mimic Raspberry Pi's downstream's driver
> +	 * behaviour.
> +	 */
> +	ret = raspberrypi_pwm_set_property(rpipwm->firmware, RPI_PWM_DEF_DUTY_REG,
> +					   duty_cycle);
> +	if (ret) {
> +		dev_err(chip->dev, "Failed to set default duty cycle: %d\n", ret);
> +		return ret;
> +	}
> +
> +        rpipwm->duty_cycle = duty_cycle;

Please use tabs for indention. (The general hint is to use checkpatch
which (I hope) tells you about problems like this.)

> +
> +	return 0;
> +}
> +
> +static const struct pwm_ops raspberrypi_pwm_ops = {
> +	.get_state = raspberrypi_pwm_get_state,
> +	.apply = raspberrypi_pwm_apply,
> +	.owner = THIS_MODULE,
> +};
> +
> +static int raspberrypi_pwm_probe(struct platform_device *pdev)
> +{
> +	struct device_node *firmware_node;
> +	struct device *dev = &pdev->dev;
> +	struct rpi_firmware *firmware;
> +	struct raspberrypi_pwm *rpipwm;
> +	int ret;
> +
> +	firmware_node = of_get_parent(dev->of_node);
> +	if (!firmware_node) {
> +		dev_err(dev, "Missing firmware node\n");
> +		return -ENOENT;
> +	}
> +
> +	firmware = devm_rpi_firmware_get(&pdev->dev, firmware_node);
> +	of_node_put(firmware_node);
> +	if (!firmware)
> +		return -EPROBE_DEFER;

Please use dev_err_probe to benefit from recording an error message in
this case.

> +	rpipwm = devm_kzalloc(&pdev->dev, sizeof(*rpipwm), GFP_KERNEL);
> +	if (!rpipwm)
> +		return -ENOMEM;
> +
> +	rpipwm->firmware = firmware;
> +	rpipwm->chip.dev = dev;
> +	rpipwm->chip.ops = &raspberrypi_pwm_ops;
> +	rpipwm->chip.base = -1;
> +	rpipwm->chip.npwm = RASPBERRYPI_FIRMWARE_PWM_NUM;
> +
> +	platform_set_drvdata(pdev, rpipwm);
> +
> +	ret = raspberrypi_pwm_get_property(rpipwm->firmware, RPI_PWM_CUR_DUTY_REG,
> +					   &rpipwm->duty_cycle);
> +	if (ret) {
> +		dev_err(dev, "Failed to get duty cycle: %d\n", ret);

Please use %pe for the error codes (directly or still better by using
dev_err_probe here, too).

> +		return ret;
> +	}
> +
> +	return pwmchip_add(&rpipwm->chip);
> +}
> [...]

Best regards
Uwe

Hi Uwe, thanks for the review.

On Tue, 2021-01-12 at 10:18 +0100, Uwe Kleine-König wrote:

[...]

> > +                duty_cycle = DIV_ROUND_CLOSEST_ULL(state->duty_cycle * RPI_PWM_MAX_DUTY,
> > +					           RPI_PWM_PERIOD_NS);
> 
> ... and round down here.
> 
> Just to be sure: writing RPI_PWM_MAX_DUTY (i.e. 255) yields 100% duty
> cycle, right?

Yes, at 255 the signal is flat.

> > +        else
> > +                duty_cycle = RPI_PWM_MAX_DUTY;
> > +
> > +	if (duty_cycle == rpipwm->duty_cycle)
> > +		return 0;
> > +
> > +	ret = raspberrypi_pwm_set_property(rpipwm->firmware, RPI_PWM_CUR_DUTY_REG,
> > +					   duty_cycle);
> > +	if (ret) {
> > +		dev_err(chip->dev, "Failed to set duty cycle: %d\n", ret);
> > +		return ret;
> > +	}
> > +
> > +	/*
> > +	 * This sets the default duty cycle after resetting the board, we
> > +	 * updated it every time to mimic Raspberry Pi's downstream's driver
> > +	 * behaviour.
> > +	 */
> > +	ret = raspberrypi_pwm_set_property(rpipwm->firmware, RPI_PWM_DEF_DUTY_REG,
> > +					   duty_cycle);
> > +	if (ret) {
> > +		dev_err(chip->dev, "Failed to set default duty cycle: %d\n", ret);
> > +		return ret;
> > +	}
> > +
> > +        rpipwm->duty_cycle = duty_cycle;
> 
> Please use tabs for indention. (The general hint is to use checkpatch
> which (I hope) tells you about problems like this.)

Sorry for that.

I took note of the rest of comments and will update the code.

Regards,
Nicolas