drm/i915/ringbuffer: Only print an error on the second attempt to reset head

There's not much we can do here but hope for the best. However the first
failure happens quite frequently and if often remedied by the second
attempt to reset HEAD. So only print the error if that attempt also
fails.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=19802Reported-by: Thomas Meyer <thomas@m3y3r.de>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: stable@kernel.org

drivers/gpu/drm/i915/intel_ringbuffer.c

@@ -156,23 +156,25 @@ static int init_ring_common(struct drm_device *dev,
 
 	/* G45 ring initialization fails to reset head to zero */
 	if (head != 0) {
-		DRM_ERROR("%s head not reset to zero "
-				"ctl %08x head %08x tail %08x start %08x\n",
-				ring->name,
-				I915_READ_CTL(ring),
-				I915_READ_HEAD(ring),
-				I915_READ_TAIL(ring),
-				I915_READ_START(ring));
+		DRM_DEBUG_KMS("%s head not reset to zero "
+			      "ctl %08x head %08x tail %08x start %08x\n",
+			      ring->name,
+			      I915_READ_CTL(ring),
+			      I915_READ_HEAD(ring),
+			      I915_READ_TAIL(ring),
+			      I915_READ_START(ring));
 
 		I915_WRITE_HEAD(ring, 0);
 
-		DRM_ERROR("%s head forced to zero "
-				"ctl %08x head %08x tail %08x start %08x\n",
-				ring->name,
-				I915_READ_CTL(ring),
-				I915_READ_HEAD(ring),
-				I915_READ_TAIL(ring),
-				I915_READ_START(ring));
+		if (I915_READ_HEAD(ring) & HEAD_ADDR) {
+			DRM_ERROR("failed to set %s head to zero "
+				  "ctl %08x head %08x tail %08x start %08x\n",
+				  ring->name,
+				  I915_READ_CTL(ring),
+				  I915_READ_HEAD(ring),
+				  I915_READ_TAIL(ring),
+				  I915_READ_START(ring));
+		}
 	}
 
 	I915_WRITE_CTL(ring,