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 ---
arch/arm/Kconfig | 25 +++++++++++-- arch/arm/include/asm/spl.h | 1 + common/spl/Makefile | 1 + common/spl/spl_semihosting.c | 71 ++++++++++++++++++++++++++++++++++++ 4 files changed, 94 insertions(+), 4 deletions(-) create mode 100644 common/spl/spl_semihosting.c
diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig index 391a77c2b4..5cacb292b5 100644 --- a/arch/arm/Kconfig +++ b/arch/arm/Kconfig @@ -403,11 +403,28 @@ 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" + 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" diff --git a/arch/arm/include/asm/spl.h b/arch/arm/include/asm/spl.h index e568af2561..b5790bd0bc 100644 --- a/arch/arm/include/asm/spl.h +++ b/arch/arm/include/asm/spl.h @@ -30,6 +30,7 @@ enum { BOOT_DEVICE_DFU, BOOT_DEVICE_XIP, BOOT_DEVICE_BOOTROM, + BOOT_DEVICE_SMH, BOOT_DEVICE_NONE }; #endif diff --git a/common/spl/Makefile b/common/spl/Makefile index db8fd36a26..e71e7bee66 100644 --- a/common/spl/Makefile +++ b/common/spl/Makefile @@ -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 diff --git a/common/spl/spl_semihosting.c b/common/spl/spl_semihosting.c new file mode 100644 index 0000000000..df6aeb2951 --- /dev/null +++ b/common/spl/spl_semihosting.c @@ -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);