[Bug 104975] Delay in skl_disable_plane() causes a system freeze

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=104975

--- Comment #51 from marc.herbert at intel.com ---
Created attachment 138830
  --> https://bugs.freedesktop.org/attachment.cgi?id=138830&action=edit
vertical corruption unless wait for vblank after disabling cursor

Could this be related? See screenshot attached and workaround by:

Kristian H. Kristensen

https://chromium-review.googlesource.com/c/chromiumos/third_party/kernel/+/877396

CHROMIUM: drm/i915: Wait for vblank after disabling cursor

The cursor disable write is latched on vsync but if we do a modeset
before that happens the write seems to be discarded and the cursor
stays on. The CURCNTL register will still read back 0 as if the write
took, but underlying hardware didn't change. We don't disable the
cursor often, so we can just force the pre-GEN9 path for cursor
that waits for vblank.

         * Unfortunately, the GEN9+ double buffering seems to be buggy when it
         * races with a modeset....

I'm guessing that this issue may well be present in upstream kernels and
regular Linux distros, the difference being that no other distro so far has
shipped with Y-tiled framebuffers.


(I doubt many distros have shipped with hardware overlays either -- Marc)

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