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author | Sean Anderson <sean.anderson@seco.com> | 2022-03-22 23:59:19 +0300 |
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committer | Tom Rini <trini@konsulko.com> | 2022-04-01 22:03:13 +0300 |
commit | 8e1c9fe243a31a0b0a40a80cc20fc3c06246d675 (patch) | |
tree | 5b76008074fe6615f96c318e9fe656c65e4c65e5 /disk | |
parent | 12a05b3bcd85ff4aa930e7a1fb8795d5a6bfdf81 (diff) | |
download | u-boot-8e1c9fe243a31a0b0a40a80cc20fc3c06246d675.tar.xz |
spl: Add semihosting boot method
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>
Diffstat (limited to 'disk')
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