[PATCH 2/5] drm/fb-helper: Fix vertical damage clipping

[Javier Martinez Canillas]

On 2/6/22 20:29, Thomas Zimmermann wrote:
> Don't clip the damage rectangle against the viewport. This only
> works if the viewport is located at the beginning of the video
> memory and the video memory doesn't extend the screen (i.e., if
> there's no overallocation).
> 
> Fbdev emulation transfers data from write operations into a
> possible shadow buffer, then into a GEM buffer object, and finally
> via graphics driver onto the screen.
> 
> If callers write outside the currently visible area, clipping the
> damage rectangle against the viewport will loose these updates in
> the shadow buffer and the fbdev's buffer object will contain stale
> data. Panning the viewport to the stale area of the buffer will
> display obsolete data.
> 
> Instead, mark all written areas as damaged, so that the damage
> handler updates the buffer object from the shadow buffer for all
> such areas. The graphics driver's later has the option of clipping
> the damaged area against the viewport when updating the screen
> from the buffer object.
> 
> Signed-off-by: Thomas Zimmermann <tzimmermann at suse.de>
> ---

Reviewed-by: Javier Martinez Canillas <javierm at redhat.com>

Best regards,
-- 
Javier Martinez Canillas
Linux Engineering
Red Hat