[ 118/171] drm/i915: Add wait_for in init_ring_common

[Greg Kroah-Hartman]

3.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Sean Paul <seanpaul@xxxxxxxxxxxx>

commit f01db988ef6f6c70a6cc36ee71e4a98a68901229 upstream.

I have seen a number of "blt ring initialization failed" messages
where the ctl or start registers are not the correct value. Upon further
inspection, if the code just waited a little bit, it would read the
correct value. Adding the wait_for to these reads should eliminate the
issue.

Signed-off-by: Sean Paul <seanpaul@xxxxxxxxxxxx>
Reviewed-by: Ben Widawsky <ben@xxxxxxxxxxxx>
Signed-off-by: Daniel Vetter <daniel.vetter@xxxxxxxx>
Signed-off-by: Julien Cristau <jcristau@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 drivers/gpu/drm/i915/intel_ringbuffer.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

--- a/drivers/gpu/drm/i915/intel_ringbuffer.c
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
@@ -295,9 +295,9 @@ static int init_ring_common(struct intel
 			| RING_VALID);
 
 	/* If the head is still not zero, the ring is dead */
-	if ((I915_READ_CTL(ring) & RING_VALID) == 0 ||
-	    I915_READ_START(ring) != obj->gtt_offset ||
-	    (I915_READ_HEAD(ring) & HEAD_ADDR) != 0) {
+	if (wait_for((I915_READ_CTL(ring) & RING_VALID) != 0 &&
+		     I915_READ_START(ring) == obj->gtt_offset &&
+		     (I915_READ_HEAD(ring) & HEAD_ADDR) == 0, 50)) {
 		DRM_ERROR("%s initialization failed "
 				"ctl %08x head %08x tail %08x start %08x\n",
 				ring->name,


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