[Intel-gfx] [PATCH] drm/i915: Mask the ring->head offset using the ring->size

[Chris Wilson]

On Tue, 17 Jan 2012 11:59:27 +0100, Daniel Vetter <daniel at ffwll.ch> wrote:
> On Tue, Nov 08, 2011 at 11:13:12PM +0000, Chris Wilson wrote:
> > Rather than relying on the hardware to do this correctly, we can
> > trivially do it ourselves.
> > 
> > This fixes a very reliable crash on d-i-n with all bits enabled during a
> > cairo-trace replay. The symptoms of the crash is that we continue to
> > write commands into the render ring buffer past the active head
> > position, leading to undefined operations.
> > 
> > Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> > Cc: stable at kernel.org
> 
> I guess this is just the usual "snb doesn't like being pushed to hard bug"
> resulting in random crashes with confusing error_states. So I think I'll
> drop this. Correct?

I could find no other reason for this to have any effect other than the
hw not playing fair so don't apply it until some one else starts
experiencing random hangs on their SNB and can confirm whether this
patch helps.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre