@@ -403,11 +403,29 @@ config ARM_SMCCC
firmware (for example, PSCI) according to SMCCC.
config SEMIHOSTING
- bool "support boot from semihosting"
+ bool "Support ARM semihosting"
help
- In emulated environments, semihosting is a way for
- the hosted environment to call out to the emulator to
- retrieve files from the host machine.
+ Semihosting is a method for a target to communicate with a host
+ debugger. It uses special instructions which the debugger will trap
+ on and interpret. This allows U-Boot to read/write files, print to
+ the console, and execute arbitrary commands on the host system.
+
+ Enabling this option will add support for reading and writing files
+ on the host system. If you don't have a debugger attached then trying
+ to do this will likely cause U-Boot to hang. Say 'n' if you are unsure.
+
+config SPL_SEMIHOSTING
+ bool "Support ARM semihosting in SPL"
+ depends on SPL
+ help
+ Semihosting is a method for a target to communicate with a host
+ debugger. It uses special instructions which the debugger will trap
+ on and interpret. This allows U-Boot to read/write files, print to
+ the console, and execute arbitrary commands on the host system.
+
+ Enabling this option will add support for reading and writing files
+ on the host system. If you don't have a debugger attached then trying
+ to do this will likely cause U-Boot to hang. Say 'n' if you are unsure.
config SYS_THUMB_BUILD
bool "Build U-Boot using the Thumb instruction set"
@@ -30,6 +30,7 @@ enum {
BOOT_DEVICE_DFU,
BOOT_DEVICE_XIP,
BOOT_DEVICE_BOOTROM,
+ BOOT_DEVICE_SMH,
BOOT_DEVICE_NONE
};
#endif
@@ -46,7 +46,7 @@ else
obj-$(CONFIG_$(SPL_TPL_)USE_ARCH_MEMSET) += memset.o
obj-$(CONFIG_$(SPL_TPL_)USE_ARCH_MEMCPY) += memcpy.o
endif
-obj-$(CONFIG_SEMIHOSTING) += semihosting.o
+obj-$(CONFIG_$(SPL_TPL_)SEMIHOSTING) += semihosting.o
obj-y += bdinfo.o
obj-y += sections.o
@@ -28,6 +28,7 @@ obj-$(CONFIG_$(SPL_TPL_)USB_STORAGE) += spl_usb.o
obj-$(CONFIG_$(SPL_TPL_)FS_FAT) += spl_fat.o
obj-$(CONFIG_$(SPL_TPL_)FS_EXT4) += spl_ext.o
obj-$(CONFIG_$(SPL_TPL_)SATA) += spl_sata.o
+obj-$(CONFIG_$(SPL_TPL_)SEMIHOSTING) += spl_semihosting.o
obj-$(CONFIG_$(SPL_TPL_)DFU) += spl_dfu.o
obj-$(CONFIG_$(SPL_TPL_)SPI_LOAD) += spl_spi.o
obj-$(CONFIG_$(SPL_TPL_)RAM_SUPPORT) += spl_ram.o
new file mode 100644
@@ -0,0 +1,71 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Copyright (C) 2022 Sean Anderson <sean.anderson@seco.com>
+ */
+
+#include <common.h>
+#include <image.h>
+#include <log.h>
+#include <semihosting.h>
+#include <spl.h>
+
+static int smh_read_full(long fd, void *memp, size_t len)
+{
+ long read;
+
+ read = smh_read(fd, memp, len);
+ if (read < 0)
+ return read;
+ if (read != len)
+ return -EIO;
+ return 0;
+}
+
+static int spl_smh_load_image(struct spl_image_info *spl_image,
+ struct spl_boot_device *bootdev)
+{
+ const char *filename = CONFIG_SPL_FS_LOAD_PAYLOAD_NAME;
+ int ret;
+ long fd, len;
+ struct image_header *header =
+ spl_get_load_buffer(-sizeof(*header), sizeof(*header));
+
+ fd = smh_open(filename, MODE_READ | MODE_BINARY);
+ if (fd < 0) {
+ log_debug("could not open %s: %ld\n", filename, fd);
+ return fd;
+ }
+
+ ret = smh_flen(fd);
+ if (ret < 0) {
+ log_debug("could not get length of image: %d\n", ret);
+ goto out;
+ }
+ len = ret;
+
+ ret = smh_read_full(fd, header, sizeof(struct image_header));
+ if (ret) {
+ log_debug("could not read image header: %d\n", ret);
+ goto out;
+ }
+
+ ret = spl_parse_image_header(spl_image, bootdev, header);
+ if (ret) {
+ log_debug("failed to parse image header: %d\n", ret);
+ goto out;
+ }
+
+ ret = smh_seek(fd, 0);
+ if (ret) {
+ log_debug("could not seek to start of image: %d\n", ret);
+ goto out;
+ }
+
+ ret = smh_read_full(fd, (void *)spl_image->load_addr, len);
+ if (ret)
+ log_debug("could not read %s: %d\n", filename, ret);
+out:
+ smh_close(fd);
+ return ret;
+}
+SPL_LOAD_IMAGE_METHOD("SEMIHOSTING", 0, BOOT_DEVICE_SMH, spl_smh_load_image);
This adds a boot method for loading the next stage from the host. It is mostly modeled off of spl_load_image_ext. I am not really sure why/how spl_load_image_fat uses three different methods to load the image, but the simple case seems to work OK for now. To control the presence of this boot method, we add a config symbol. While we're at it, we update the original semihosting config symbol. I think semihosting has some advantages of other forms of JTAG boot. Common other ways to boot from JTAG include: - Implementing DDR initialization through JTAG (typically with dozens of lines of TCL) and then loading U-Boot. The DDR initialization typically uses hard-coded register writes, and is not easily adapted to different boards. BOOT_DEVICE_SMH allows booting with SPL, leveraging U-Boot's existing DDR initialization code. This is the method used by NXP's CodeWarrior IDE on Layerscape processors (see AN12270). - Loading a bootloader into SDRAM, waiting for it to initialize DDR, and then loading U-Boot. This is tricky, because the debugger must stop the boot after the bootloader has completed its work. Trying to load U-Boot too early can cause failure to boot. This is the method used by Xilinx with its Zynq(MP) processors. - Loading SPL with BOOT_DEVICE_RAM and breaking before SPL loads the image to load U-Boot at the appropriate place. This can be a bit tricky, because the load address is dependent on the header size. An elf with symbols must also be used in order to stop at the appropriate point. BOOT_DEVICE_SMH can be viewed as an extension of this process, where SPL automatically stops and tells the host where to place the image. Signed-off-by: Sean Anderson <sean.anderson@seco.com> --- (no changes since v2) Changes in v2: - Compile arch/arm/lib/semihosting.o in SPL - Make CONFIG_SPL_SEMIHOSTING depend on SPL arch/arm/Kconfig | 26 +++++++++++-- arch/arm/include/asm/spl.h | 1 + arch/arm/lib/Makefile | 2 +- common/spl/Makefile | 1 + common/spl/spl_semihosting.c | 71 ++++++++++++++++++++++++++++++++++++ 5 files changed, 96 insertions(+), 5 deletions(-) create mode 100644 common/spl/spl_semihosting.c