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board: axy17lte: get board usable - add bootcmd and docs

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U-boot is intended to replace linux kernel in android boot image(ABL), and
it's FIT payload to replace initramfs file. The boot process is similar to
boot image with linux:
- android bootloader (ABL) unpacks android boot image
- ABL sets `linux,initrd-start property` in chosen node in unpacked FDT
- ABL sets x0 register to FDT address, and passes control to u-boot
- u-boot reads x0 register, and stores it in `prevbl_fdt_addr` env variable
- u-boot reads `linux,initrd-start` property,
and stores it in `prevbl_initrd_start_addr`

In this way, u-boot bootcmd relies on `prevbl_initrd_start_addr` env
variable, and boils down to `bootm $prevbl_initrd_start_addr`.
If more control on boot process is desired, pack a boot script in
FIT image, and put it to default configuration

What done:
- Rearrange defconfig option order
- Add CONFIG_SAVE_PREV_BL_* options
- Doc updates:
  - remove wrong SBOOT memory corruption note, because
  memory is changed during u-boot bringup process,
  not by SBOOT
  - put payload on ramdisk place in abl boot image
  creation step

Signed-off-by: Dzmitry Sankouski <dsankouski@gmail.com>
This commit is contained in:
Dzmitry Sankouski
2022-02-22 21:49:54 +03:00
committed by Tom Rini
parent f8a1b33889
commit d5c4ec4aa3
5 changed files with 16 additions and 12 deletions
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15
doc/board/samsung/axy17lte.rst
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@@ -66,26 +66,17 @@ and is therefore SBOOT's payload.
It may be pure u-boot (with loading u-boot's payload from flash in mind),
or u-boot + u-boot's payload.
It should be kept in mind, that SBOOT binary patches it's payload after loading
in address range 0x401f8550-0x401f9280. Given SBOOT loads payload to 0x40001000,
a range of 0x1f7550-0x1f8280 (2061648-2065024) in a payload file
will be corrupted after loading to RAM.
Creating payload file
"""""""""""""""""""""
- Assemble FIT image for your kernel
- Create a file for u-boot payload ``touch sboot-payload``
- Write zeroes till 0x200000 address to be sure SBOOT won't corrupt your info
``dd if=/dev/zero of=sboot-payload bs=$((0x200000)) count=1``
- Write u-boot to the start of the payload ``dd if=<u-boot.bin path> of=sboot-payload``
- Write FIT image to payload from 0x200000 address
``dd if=<FIT image path> of=sboot-payload seek=1 bs=2M``
Creating android boot image
"""""""""""""""""""""""""""
Once payload created, it's time for android image::
mkbootimg --base 0x40000000 --kernel_offset 0x00000000 --ramdisk_offset 0x01000000 --tags_offset 0x00000100 --pagesize 2048 --second_offset 0x00f00000 --kernel <sboot-payload path> -o uboot.img
uboot=<path to u-boot.bin file>
ramdisk=<path to FIT payload file>
mkbootimg --base 0x40000000 --kernel_offset 0x00000000 --ramdisk_offset 0x01000000 --tags_offset 0x00000100 --pagesize 2048 --second_offset 0x00f00000 --kernel "$uboot" --ramdisk "$ramdisk" -o uboot.img
Note, that stock Samsung bootloader ignores offsets, set in mkbootimg.