[PATCH 3.13 168/259] drm/i915: Reorder the semaphore deadlock check, again

[Kamal Mostafa]

3.13.11.6 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Chris Wilson <chris at chris-wilson.co.uk>

commit a0d036b074b4a5a933e37fcb9bdd6b3cc80a0387 upstream.

commit 4be173813e57c7298103a83155c2391b5b167b4c
Author: Chris Wilson <chris at chris-wilson.co.uk>
Date:   Fri Jun 6 10:22:29 2014 +0100

    drm/i915: Reorder semaphore deadlock check

did the majority of the work, but it missed one crucial detail:

The check for the unkickable deadlock on this ring must come after the
check whether the ring that we are waiting on has already passed its
target seqno.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=80709
Tested-by: Stefan Huber <shuber at sthu.org>
Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala at intel.com>
Cc: Jani Nikula <jani.nikula at intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter at ffwll.ch>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 drivers/gpu/drm/i915/i915_irq.c | 11 ++++-------
 1 file changed, 4 insertions(+), 7 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
index 2093c72..3a10da2 100644
--- a/drivers/gpu/drm/i915/i915_irq.c
+++ b/drivers/gpu/drm/i915/i915_irq.c
@@ -2392,7 +2392,7 @@ static int semaphore_passed(struct intel_ring_buffer *ring)
 {
 	struct drm_i915_private *dev_priv = ring->dev->dev_private;
 	struct intel_ring_buffer *signaller;
-	u32 seqno, ctl;
+	u32 seqno;
 
 	ring->hangcheck.deadlock++;
 
@@ -2404,15 +2404,12 @@ static int semaphore_passed(struct intel_ring_buffer *ring)
 	if (signaller->hangcheck.deadlock >= I915_NUM_RINGS)
 		return -1;
 
-	/* cursory check for an unkickable deadlock */
-	ctl = I915_READ_CTL(signaller);
-	if (ctl & RING_WAIT_SEMAPHORE && semaphore_passed(signaller) < 0)
-		return -1;
-
 	if (i915_seqno_passed(signaller->get_seqno(signaller, false), seqno))
 		return 1;
 
-	if (signaller->hangcheck.deadlock)
+	/* cursory check for an unkickable deadlock */
+	if (I915_READ_CTL(signaller) & RING_WAIT_SEMAPHORE &&
+	    semaphore_passed(signaller) < 0)
 		return -1;
 
 	return 0;
-- 
1.9.1