[PATCH v3 11/29] spl: Add semihosting boot method
Sean Anderson
sean.anderson at seco.com
Tue Mar 22 21:59:19 CET 2022
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 at 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
diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 64acbda254..408d96ac8e 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -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"
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/arch/arm/lib/Makefile b/arch/arm/lib/Makefile
index c48e1f622d..594fc1228a 100644
--- a/arch/arm/lib/Makefile
+++ b/arch/arm/lib/Makefile
@@ -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_$(SPL_TPL_)SEMIHOSTING) += semihosting.o
obj-y += bdinfo.o
obj-y += sections.o
diff --git a/common/spl/Makefile b/common/spl/Makefile
index db8fd36a26..e71e7bee66 100644
--- a/common/spl/Makefile
+++ b/common/spl/Makefile
@@ -28,6 +28,7 @@ obj-$(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 at 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);
--
2.25.1
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