Revert: drm/i915: correctly order the ring init sequence

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>

diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
index 12a9e5fd925272c5151cd152a20239cd18983671..302d3d54fb416a20c5c01def8ffde5755336fbb9 100644 (file)
--- 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_ring_buffer *ring)
        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_ring_buffer *ring)
                }
        }
 
-       /* 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);