[Intel-gfx] Acid-like effect in dark regions on key press

[Chris Wilson]

Hello all,

I'm seeing a bizarre problem whilst running wayland/cairo-drm/i915 under
KMS. Occasionally after pressing a key (which is handled by wayland
through the input layer) the dark regions (I'm estimating where the
value is less than ~4) become garbage. I've managed to capture a
screenshot before and afterwards (which implies that the scan-out buffer
was read back through the GTT and remained as the scan-out buffer with
the effect still apparent) - only the read back image is perfect and
shows no artefact. After a while (with no interaction and I think no
execution of batch buffers), the display magically returns to normal.

I'm open to suggestions as how to diagnose this problem and track down
the cause. Thanks.
-ickle