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Subject[ 218/218] Revert: drm/i915: correctly order the ring init sequence
Date
3.4-stable review patch.  If anyone has any objections, please let me know.

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

From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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@canonical.com>
Cc: Andreas Sturmlechner <andreas.sturmlechner@gmail.com>
Cc: Jani Nikula <jani.nikula@intel.com>
Cc: Yang Guang <guang.a.yang@intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
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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