drm/i915: Reorder the semaphore deadlock check, again

commit 4be173813e57c7298103a83155c2391b5b167b4c
Author: Chris Wilson <chris@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@sthu.org>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@intel.com>
Cc: Jani Nikula <jani.nikula@intel.com>
Cc: stable@vger.kernel.org
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

1 files changed, 4 insertions, 7 deletions

diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
index 267f069765ad..c05c84f3f091 100644
--- a/drivers/gpu/drm/i915/i915_irq.c
+++ b/drivers/gpu/drm/i915/i915_irq.c
@@ -2845,7 +2845,7 @@ 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++;
 
@@ -2857,15 +2857,12 @@ 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;