[Intel-gfx] [PATCH 2/3] drm/i915/tgl: Make sure a semiplanar UV plane is tile row size aligned

[Chris Wilson]

Quoting Imre Deak (2019-12-27 23:51:46)
> Currently the start address of a UV plane in a semiplanar YUV FB is tile
> size (4kB) aligned. I noticed, that enforcing only this alignment leads
> oddly to random memory corruptions on TGL while scanning out Y-tiled
> FBs. This issue can be easily reproduced with a UV plane that is not
> aligned to the plane's tile row size.
> 
> Some experiments showed the correct alignment to be tile row size
> indeed. This also makes sense, since the de-tiling fence created for the

One would expect the implicit fence to follow the fence detiling HW
logic, which does not require tile-row alignment, just 4096 alignment
(since gen4). That suggests this logic is peculiar to the display engine.

> object - with its own stride and so "left" and "right" edge - applies to
> all the planes in the FB, so each tile row of all planes should be tile
> row aligned.
> 
> In fact BSpec requires this alignment since SKL. On SKL we may enforce
> this due to the AUX plane x,y coords check, but on ICL and TGL we don't.
> For now enforce this only on TGL; I can follow up with any necessary
> change for ICL after more tests.

Considering the severity of the error, I strongly suggest we fix all
suspected machines and Cc:stable.

> BSpec requires a stricter alignment for linear UV planes too (kind of a
> tile row alignment), but it's unclear whether that's really needed
> (couldn't be explained with the de-tiling fence as above) and enforcing
> that could break existing user space; so avoid that too for now until
> more tests.
> 
> Cc: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
> Signed-off-by: Imre Deak <imre.deak at intel.com>
> ---
> +static unsigned int intel_tile_row_size(const struct drm_framebuffer *fb,
> +                                       int color_plane)
> +{
> +       unsigned int tile_width, tile_height;
> +
> +       intel_tile_dims(fb, color_plane, &tile_width, &tile_height);
> +
> +       return fb->pitches[color_plane] * tile_height;

Ok, that is tile_row_size.
-Chris