[ 218/218] Revert: drm/i915: correctly order the ring init sequence

[Greg Kroah-Hartman]

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

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

From: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

This reverts commit 57ecc93ce680b1ace1f9e79d588dabe32353202c which
really is commit 0d8957c8a90bbb5d34fab9a304459448a5131e06 upstream as it
has been reported to cause problems in the 3.4.y kernel series.

Reported-by: Herton Ronaldo Krzesinski <herton.krzesinski@xxxxxxxxxxxxx>
Cc: Andreas Sturmlechner <andreas.sturmlechner@xxxxxxxxx>
Cc: Jani Nikula <jani.nikula@xxxxxxxxx>
Cc: Yang Guang <guang.a.yang@xxxxxxxxx>
Cc: Daniel Vetter <daniel.vetter@xxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/gpu/drm/i915/intel_ringbuffer.c |    7 ++-----
 1 file changed, 2 insertions(+), 5 deletions(-)

--- a/drivers/gpu/drm/i915/intel_ringbuffer.c
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
@@ -258,6 +258,8 @@ static int init_ring_common(struct intel
 	I915_WRITE_HEAD(ring, 0);
 	ring->write_tail(ring, 0);
 
+	/* Initialize the ring. */
+	I915_WRITE_START(ring, obj->gtt_offset);
 	head = I915_READ_HEAD(ring) & HEAD_ADDR;
 
 	/* G45 ring initialization fails to reset head to zero */
@@ -283,11 +285,6 @@ static int init_ring_common(struct intel
 		}
 	}
 
-	/* Initialize the ring. This must happen _after_ we've cleared the ring
-	 * registers with the above sequence (the readback of the HEAD registers
-	 * also enforces ordering), otherwise the hw might lose the new ring
-	 * register values. */
-	I915_WRITE_START(ring, obj->gtt_offset);
 	I915_WRITE_CTL(ring,
 			((ring->size - PAGE_SIZE) & RING_NR_PAGES)
 			| RING_VALID);


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