[Intel-gfx] [PATCH] drm/i915: Fix ADL+ tiled plane stride when the POT stride is smaller than the original

[Imre Deak]

On Mon, Dec 04, 2023 at 10:24:43PM +0200, Ville Syrjala wrote:
> From: Ville Syrjälä <ville.syrjala at linux.intel.com>
> 
> plane_view_scanout_stride() currently assumes that we had to pad the
> mapping stride with dummy pages in order to align it. But that is not
> the case if the original fb stride exceeds the aligned stride used
> to populate the remapped view, which is calculated from the user
> specified framebuffer width rather than the user specified framebuffer
> stride.
> 
> Ignore the original fb stride in this case and just stick to the POT
> aligned stride. Getting this wrong will cause the plane to fetch the
> wrong data, and can lead to fault errors if the page tables at the
> bogus location aren't even populated.
> 
> TODO: figure out if this is OK for CCS, or if we should instead increase
> the width of the view to cover the entire user specified fb stride
> instead...

Yes, this is also needed since the CCS AUX surface can't be remapped in
general (unless its stride is page size aligned -> main surface stride
256 tiles aligned).

> Cc: Imre Deak <imre.deak at intel.com>
> Cc: Juha-Pekka Heikkila <juhapekka.heikkila at gmail.com>
> Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>

Thanks for the fix, with the above CCS case also fixed as a follow-up or
in this patch:
Reviewed-by: Imre Deak <imre.deak at intel.com>

> ---
>  drivers/gpu/drm/i915/display/intel_fb.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_fb.c b/drivers/gpu/drm/i915/display/intel_fb.c
> index 33a693460420..ab634a4c86d1 100644
> --- a/drivers/gpu/drm/i915/display/intel_fb.c
> +++ b/drivers/gpu/drm/i915/display/intel_fb.c
> @@ -1381,7 +1381,8 @@ plane_view_scanout_stride(const struct intel_framebuffer *fb, int color_plane,
>  	struct drm_i915_private *i915 = to_i915(fb->base.dev);
>  	unsigned int stride_tiles;
>  
> -	if (IS_ALDERLAKE_P(i915) || DISPLAY_VER(i915) >= 14)
> +	if ((IS_ALDERLAKE_P(i915) || DISPLAY_VER(i915) >= 14) &&
> +	    src_stride_tiles < dst_stride_tiles)
>  		stride_tiles = src_stride_tiles;
>  	else
>  		stride_tiles = dst_stride_tiles;
> -- 
> 2.41.0
>