Re: [PATCH 1/4] drm/amd/display: Adjust plane init for off by one error

[Harry Wentland <harry.wentland@amd.com>]

On 2025-01-21 08:57, Mario Limonciello wrote:
> From: Mario Limonciello <mario.limonciello@amd.com>
> 
> The number of active surfaces is initialized to the number
> of active planes.  If the number of planes aren't initialized
> properly then the last plane can end up not getting initialized
> which can be a divide by zero error.
> 
> Reported-and-tested-by: Luke Jones <luke@ljones.dev>
> Closes: https://gitlab.freedesktop.org/drm/amd/-/issues/3794
> Closes: https://gitlab.freedesktop.org/drm/amd/-/issues/3533
> Fixes: 7966f319c66d9 ("drm/amd/display: Introduce DML2")
> Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
> ---
>  drivers/gpu/drm/amd/display/dc/dml2/display_mode_core.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/amd/display/dc/dml2/display_mode_core.c b/drivers/gpu/drm/amd/display/dc/dml2/display_mode_core.c
> index 8dabb1ac0b684..45147b812d7d9 100644
> --- a/drivers/gpu/drm/amd/display/dc/dml2/display_mode_core.c
> +++ b/drivers/gpu/drm/amd/display/dc/dml2/display_mode_core.c
> @@ -6787,7 +6787,7 @@ dml_bool_t dml_core_mode_support(struct display_mode_lib_st *mode_lib)
>  		}
>  	}
>  
> -	for (k = 0; k <= mode_lib->ms.num_active_planes - 1; k++) {
> +	for (k = 0; k <= mode_lib->ms.num_active_planes; k++) {

Shouldn't this be either
	k <= num_active_planes -1
or
	k < num_active_planes
?

Is num_active_planes wrong somehow?

Harry

>  		CalculateBytePerPixelAndBlockSizes(
>  								mode_lib->ms.cache_display_cfg.surface.SourcePixelFormat[k],
>  								mode_lib->ms.cache_display_cfg.surface.SurfaceTiling[k],