commit 4be173813e57c7298103a83155c2391b5b167b4c
Author: Chris Wilson <[email protected]>
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 <[email protected]>
Signed-off-by: Chris Wilson <[email protected]>
Cc: Mika Kuoppala <[email protected]>
Cc: Jani Nikula <[email protected]>
Cc: [email protected]
---
 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 ce02a2d..95ba903 100644
--- a/drivers/gpu/drm/i915/i915_irq.c
+++ b/drivers/gpu/drm/i915/i915_irq.c
@@ -3110,7 +3110,7 @@ static int semaphore_passed(struct intel_engine_cs *ring)
 {
        struct drm_i915_private *dev_priv = ring->dev->dev_private;
        struct intel_engine_cs *signaller;
-       u32 seqno, ctl;
+       u32 seqno;
 
        ring->hangcheck.deadlock++;
 
@@ -3122,15 +3122,12 @@ static int semaphore_passed(struct intel_engine_cs 
*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

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