Re: [PATCH 4/6] drm/msm/a8xx: use pipe protect slot 15 for last-span-unbound feature

[Konrad Dybcio]

On 4/1/26 4:17 AM, Alexander Koskovich wrote:
> A8XX GPUs have two sets of protect registers: 64 global slots and 16
> pipe specific slots. The last-span-unbound feature is only available
> on pipe protect registers, and should always target pipe slot 15.
> 
> This matches the downstream driver which hardcodes pipe slot 15 for
> all A8XX GPUs (GRAPHICS.LA.15.0.r1) and resolves protect errors on
> A810.
> 
> Signed-off-by: Alexander Koskovich <akoskovich@xxxxx>
> ---
>  drivers/gpu/drm/msm/adreno/a8xx_gpu.c | 9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/msm/adreno/a8xx_gpu.c b/drivers/gpu/drm/msm/adreno/a8xx_gpu.c
> index 5af82d43f1e4..63387ee9b04a 100644
> --- a/drivers/gpu/drm/msm/adreno/a8xx_gpu.c
> +++ b/drivers/gpu/drm/msm/adreno/a8xx_gpu.c
> @@ -252,11 +252,12 @@ static void a8xx_set_cp_protect(struct msm_gpu *gpu)
>  	}
>  
>  	/*
> -	 * Last span feature is only supported on PIPE specific register.
> -	 * So update those here
> +	 * Last span setting is only being applied to the last pipe specific
> +	 * register. Hence duplicate the last span from protect reg into the
> +	 * BR and BV protect reg pipe 15.
>  	 */
> -	a8xx_write_pipe(gpu, PIPE_BR, REG_A8XX_CP_PROTECT_PIPE(protect->count_max), final_cfg);
> -	a8xx_write_pipe(gpu, PIPE_BV, REG_A8XX_CP_PROTECT_PIPE(protect->count_max), final_cfg);
> +	a8xx_write_pipe(gpu, PIPE_BR, REG_A8XX_CP_PROTECT_PIPE(15), final_cfg);
> +	a8xx_write_pipe(gpu, PIPE_BV, REG_A8XX_CP_PROTECT_PIPE(15), final_cfg);

I think this is a better fix than:

https://lore.kernel.org/linux-arm-msm/20260225-glymur-protect-fix-v1-1-0deddedf9277@xxxxxxxxxxxxxxxx/

which will let us bring back the BUILD_BUG_ON.. WDYT Akhil?

FWIW KGSL just hardcodes the number 15 here as well.. may make it
configurable if that ever changes

Reviewed-by: Konrad Dybcio <konrad.dybcio@xxxxxxxxxxxxxxxx>

Konrad