[Intel-gfx] [PATCH] drm/i915: Clear scanline waits before disabling the pipe.

[Eric Anholt]

On Sun,  8 Aug 2010 12:01:38 +0100, Chris Wilson <chris at chris-wilson.co.uk> wrote:
> If we disable the pipe and the GPU is currently waiting on a scanline
> WAIT_FOR_EVENT, the GPU will hang. Fortunately, there is a magic bit
> which we can write on i915+ to break this wait before disabling the
> pipe.
> 
> References:
> 
>   Bug 29252 - [Arrandale] Hung WAIT_FOR_EVENT when running rss-glx-skyrocket
>   https://bugs.freedesktop.org/show_bug.cgi?id=29252
> 
>   Bug 28964 - [i965gm] GPU infinite MI_WAIT_FOR_EVENT while watching video in Totem
>   https://bugs.freedesktop.org/show_bug.cgi?id=28964
> 
> and many others.
> 
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Jesse Barnes <jbarnes at virtuousgeek.org>

At one point I thought we were taking the lock and idling the GPU before
a modeset, which would handle this problem, right?  This doesn't seem
reliable if we aren't, as we may just have not reached the MI_WAIT_FOR_EVENT
in the ring yet.
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