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

[Juha-Pekka Heikkila]

I tried a bit if I can break something with ccs but it seemed everything 
work as expected with this fix.

Reviewed-by: Juha-Pekka Heikkila <juhapekka.heikkila at gmail.com>

On 4.12.2023 22.24, 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...
> 
> 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>
> ---
>   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;