From 075b68c315c9f1c02565576e1f412029993472c0 Mon Sep 17 00:00:00 2001
From: Chris Wilson <chris@chris-wilson.co.uk>
Date: Wed, 5 Jun 2013 10:08:35 +0100
Subject: [PATCH 2/2] drm/i915: Don't count semaphore waits towards a stuck
 ring

If we detect a ring is in a valid wait for another, just let it be.
Eventually it will either begin to progress again, or the entire system
will come grinding to a halt and then hangcheck will fire as soon as the
deadlock is detected.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/i915_irq.c |   55 +++++++++++++++++++++++++++------------
 1 file changed, 38 insertions(+), 17 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
index e936fde..ae3e299 100644
--- a/drivers/gpu/drm/i915/i915_irq.c
+++ b/drivers/gpu/drm/i915/i915_irq.c
@@ -2331,33 +2331,50 @@ static bool i915_hangcheck_ring_idle(struct intel_ring_buffer *ring,
 	return false;
 }
 
-static bool semaphore_passed(struct intel_ring_buffer *ring)
+static struct intel_ring_buffer *
+semaphore_waits_for(struct intel_ring_buffer *ring, u32 *acthd)
 {
 	struct drm_i915_private *dev_priv = ring->dev->dev_private;
-	u32 acthd = intel_ring_get_active_head(ring) & HEAD_ADDR;
-	struct intel_ring_buffer *signaller;
 	u32 cmd, ipehr, acthd_min;
 
 	ipehr = I915_READ(RING_IPEHR(ring->mmio_base));
 	if ((ipehr & ~(0x3 << 16)) !=
 	    (MI_SEMAPHORE_MBOX | MI_SEMAPHORE_COMPARE | MI_SEMAPHORE_REGISTER))
-		return false;
+		return NULL;
 
 	/* ACTHD is likely pointing to the dword after the actual command,
 	 * so scan backwards until we find the MBOX.
 	 */
-	acthd_min = max((int)acthd - 3 * 4, 0);
+	*acthd = intel_ring_get_active_head(ring) & HEAD_ADDR;
+	acthd_min = max((int)*acthd - 3 * 4, 0);
 	do {
-		cmd = ioread32(ring->virtual_start + acthd);
+		cmd = ioread32(ring->virtual_start + *acthd);
 		if (cmd == ipehr)
 			break;
 
-		acthd -= 4;
-		if (acthd < acthd_min)
-			return false;
+		*acthd -= 4;
+		if (*acthd < acthd_min)
+			return NULL;
 	} while (1);
 
-	signaller = &dev_priv->ring[(ring->id + (((ipehr >> 17) & 1) + 1)) % 3];
+	return &dev_priv->ring[(ring->id + (((ipehr >> 17) & 1) + 1)) % 3];
+}
+
+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 acthd, ctl;
+
+	signaller = semaphore_waits_for(ring, &acthd);
+	if (signaller == NULL || signaller == ring)
+		return -1;
+
+	/* cursory check for an unkickable deadlock */
+	ctl = I915_READ_CTL(signaller);
+	if (ctl & RING_WAIT_SEMAPHORE && semaphore_passed(signaller) <= 0)
+		return -1;
+
 	return i915_seqno_passed(signaller->get_seqno(signaller, false),
 				 ioread32(ring->virtual_start+acthd+4)+1);
 }
@@ -2374,13 +2391,17 @@ static bool kick_ring(struct intel_ring_buffer *ring)
 		return true;
 	}
 
-	if (INTEL_INFO(dev)->gen >= 6 &&
-	    tmp & RING_WAIT_SEMAPHORE &&
-	    semaphore_passed(ring)) {
-		DRM_ERROR("Kicking stuck semaphore on %s\n",
-			  ring->name);
-		I915_WRITE_CTL(ring, tmp);
-		return true;
+	if (INTEL_INFO(dev)->gen >= 6 && tmp & RING_WAIT_SEMAPHORE) {
+		switch (semaphore_passed(ring)) {
+		default:
+			return false;
+		case 1:
+			DRM_ERROR("Kicking stuck semaphore on %s\n",
+				  ring->name);
+			I915_WRITE_CTL(ring, tmp);
+		case 0:
+			return true;
+		}
 	}
 	return false;
 }
-- 
1.7.10.4