[PATCH v1] docs: Correct FW_JUMP_FDT_ADDR calculation example

[Gabriel Somlo <gsomlo@gmail.com>]

On Thu, Mar 23, 2023 at 06:18:00PM +0100, Andrew Jones wrote:
> On Wed, Mar 22, 2023 at 01:04:48PM -0400, Gabriel Somlo wrote:
> > When using `PLATFORM=generic` defaults, the kernel is loaded at
> > `FW_JUMP_ADDR = FW_TEXT_START + 0x200000`, and the FDT is loaded at
> > `FW_JUMP_FDT_ADDR = FW_TEXT_START + 0x2200000`.
> > 
> > Therefore, the maximum kernel size before `FW_JUMP_FDT_ADDR` must
> > be increased is the difference, or `0x2000000`.
> 
> Sounds good, but this is only correct for RV64. For RV32 it should be
> 0x1e00000. I wonder if we should do something like
> 
>    ```
>    ${CROSS_COMPILE}objdump -h $KERNEL_ELF | sort -k 5,5 | awk -n '/^ +[0-9]+ /\
>    {addr="0x"$3; size="0x"$5; printf "0x""%x\n",addr+size}' \
> -  | (( `tail -1` > 0x2200000 )) && echo fdt overlaps kernel,\
> -  increase FW_JUMP_FDT_ADDR
> +  | (( `tail -1` > (FW_JUMP_FDT_ADDR - FW_JUMP_ADDR) )) && echo fdt overlaps \
> +  kernel, increase FW_JUMP_FDT_ADDR
> 
>    ${LLVM}objdump -h --show-lma $KERNEL_ELF | sort -k 5,5 | \
>    awk -n '/^ +[0-9]+ / {addr="0x"$3; size="0x"$5; printf "0x""%x\n",addr+size}'\
> -  | (( `tail -1` > 0x2200000 )) && echo fdt overlaps kernel,\
> -  increase FW_JUMP_FDT_ADDR
> +  | (( `tail -1` > (FW_JUMP_FDT_ADDR - FW_JUMP_ADDR) )) && echo fdt overlaps \
> +  kernel, increase FW_JUMP_FDT_ADDR
>    ```
> 
> instead?

Yeah, v2 (with a commit blurb updated to match) should be on its way.

Thanks,
--Gabriel