drm/i915: Reorder the semaphore deadlock check, again

BugLink: http://bugs.launchpad.net/bugs/1356913

commit a0d036b upstream.

commit 4be1738
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]>
Signed-off-by: Daniel Vetter <[email protected]>
Signed-off-by: Kamal Mostafa <[email protected]>
Signed-off-by: Joseph Salisbury <[email protected]>

Author: ickle

drivers/gpu/drm/i915/i915_irq.c

@@ -2394,7 +2394,7 @@ 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++;
 
@@ -2406,15 +2406,12 @@ 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;