[Acked] Re: natty cherry-pick request: drm/i915: Fix gen6 (SNB) missed BLT ring interrupts.

[Leann Ogasawara]

On Tue, 2011-06-21 at 11:38 -0400, Robert Hooker wrote:
> Please consider pulling the following change into natty to fix LP #761065.
> 
> SRU Justification:
>  Fixes a constant stream of hangcheck errors flooding dmesg, and
> removes the visible stuttering that was caused by it when using 3D
> applications.
> Impact:
>  Fixes missed interrupts on sandybridge GPU's. It doesn't affect any
> other GPU generation.
> Fix:
>  Upstream commit 498e720b96379d8ee9c294950a01534a73defcf3.
> Testcase:
>  1) Install mesa-utils on a system using sandybridge graphics on 11.04
>  2) run vblank_mode=0 glxgears and let it run for 30 seconds or so
>  3) kill it then check dmesg
>  4) Without fix: hangcheck messages every ~5 seconds, massive
> stuttering of the whole desktop observed. With fix: no hangcheck
> messages, able to continue using the desktop.

Don't forget to add the above SRU Justification, Impact, and Testcase to
the bug description for the SRU Team.

> This was sent to stable, but 2.6.38.y stable is dead so it will need
> to be manually cherry-picked. It has been tested extensively locally
> as well as by users on the bug whom I provided test kernels for. It
> applies cleanly to ubuntu-natty.git.
> 
> http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=498e720b96379d8ee9c294950a01534a73defcf3
> 
> 
> 
> drm/i915: Fix gen6 (SNB) missed BLT ring interrupts.
> 
> The failure appeared in dmesg as:
> 
> [drm:i915_hangcheck_ring_idle] *ERROR* Hangcheck timer elapsed... blt
> ring idle [waiting on 35064155, at 35064155], missed IRQ?
> 
> This works around that problem on by making the blitter command
> streamer write interrupt state to the Hardware Status Page when a
> MI_USER_INTERRUPT command is decoded, which appears to force the seqno
> out to memory before the interrupt happens.
> 
> v1->v2: Moved to prior interrupt handler installation and RMW flags as
> per feedback.
> v2->v3: Removed RMW of flags (by anholt)
> 
> Cc: stable at kernel.org
> Signed-off-by: Daniel J Blueman <daniel.blueman at gmail.com>
> Signed-off-by: Eric Anholt <eric at anholt.net>
> Tested-by: Chris Wilson <chris at chris-wilson.co.uk> [v1]
> Tested-by: Eric Anholt <eric at anholt.net> [v1,v3]
>    (incidence of the bug with a testcase went from avg 2/1000 to
>    0/12651 in the latest test run (plus more for v1))
> Tested-by: Kenneth Graunke <kenneth at whitecape.org> [v1]
> Tested-by: Robert Hooker <robert.hooker at canonical.com> [v1]
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=33394
> Signed-off-by: Dave Airlie <airlied at redhat.com>

Looks reasonable for Natty SRU with minimal risk of regression and has
positive test results.

Acked-by: Leann Ogasawara <leann.ogasawara at canonical.com>