[PATCH] drm/i915: Fix gen6 (SNB) missed BLT ring interrupts.

From: Eric Anholt
Date: Fri Jun 17 2011 - 14:42:18 EST

From: Daniel J Blueman <daniel.blueman@xxxxxxxxx>

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@xxxxxxxxxx
Signed-off-by: Daniel J Blueman <daniel.blueman@xxxxxxxxx>
Signed-off-by: Eric Anholt <eric@xxxxxxxxxx>
Tested-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> [v1]
Tested-by: Eric Anholt <eric@xxxxxxxxxx> [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@xxxxxxxxxxxxx> [v1]
Tested-by: Robert Hooker <robert.hooker@xxxxxxxxxxxxx> [v1]
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=33394
drivers/gpu/drm/i915/i915_irq.c | 10 ++++++++++
1 files changed, 10 insertions(+), 0 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
index b79619a..0263717 100644
--- a/drivers/gpu/drm/i915/i915_irq.c
+++ b/drivers/gpu/drm/i915/i915_irq.c
@@ -1740,6 +1740,16 @@ void ironlake_irq_preinstall(struct drm_device *dev)
INIT_WORK(&dev_priv->rps_work, gen6_pm_rps_work);

I915_WRITE(HWSTAM, 0xeffe);
+ if (IS_GEN6(dev)) {
+ /* Workaround stalls observed on Sandy Bridge GPUs by
+ * making the blitter command streamer generate a
+ * write to the Hardware Status Page for
+ * MI_USER_INTERRUPT. This appears to serialize the
+ * previous seqno write out before the interrupt
+ * happens.
+ */
+ }

/* XXX hotplug from PCH */


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