[PATCH] ARM: pbl: uncompress: add comment explaining order of operations

[Sascha Hauer]

On Sat, Apr 03, 2021 at 09:03:46AM +0200, Ahmad Fatoum wrote:
> When the PBL runs from flash, it relocates to RAM prior to extracting
> barebox proper. It does the sneaky thing of _not_ relocating the piggy
> data though, so read from flash and uncompression may latter happen
> at the same time.
> 
> For this to work, it's critical that the variables pointing at the piggy
> data are evaluated before relocation. ARM does so and carefully uses
> them to derive the address of the PBL size later on instead of
> evaluating image_data_end again.
> 
> When I ported the same code for RISC-V use, this got lost. Add a comment
> explaining the criticality of maintaining this order of operations.
> 
> Signed-off-by: Ahmad Fatoum <ahmad at a3f.at>
> ---
>  arch/arm/cpu/uncompress.c | 1 +
>  1 file changed, 1 insertion(+)

Applied, thanks

Sascha

> 
> diff --git a/arch/arm/cpu/uncompress.c b/arch/arm/cpu/uncompress.c
> index db0fe98e0d83..2250b8ccd375 100644
> --- a/arch/arm/cpu/uncompress.c
> +++ b/arch/arm/cpu/uncompress.c
> @@ -52,6 +52,7 @@ void __noreturn barebox_pbl_start(unsigned long membase, unsigned long memsize,
>  	void *pg_start, *pg_end;
>  	unsigned long pc = get_pc();
>  
> +	/* piggy data is not relocated, so determine the bounds now */
>  	pg_start = input_data + global_variable_offset();
>  	pg_end = input_data_end + global_variable_offset();
>  
> -- 
> 2.30.0
> 
> 
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> 

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