drm/i915: SNB BLT workaround

On some stepping of SNB cpu, the first command to be parsed in BLT
command streamer should be MI_BATCHBUFFER_START otherwise the GPU
may hang.

(cherry picked from commit 8d19215be8254f4f75e9c5a0d28345947b0382db)

Conflicts:

	drivers/gpu/drm/i915/intel_ringbuffer.c
	drivers/gpu/drm/i915/intel_ringbuffer.h

Signed-off-by: Zou Nan hai <nanhai.zou@intel.com>
Cc: stable@kernel.org
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

1 files changed, 3 insertions, 0 deletions

diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.h b/drivers/gpu/drm/i915/intel_ringbuffer.h
index a05aff0e5764..3126c2681983 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.h
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.h
@@ -63,6 +63,7 @@ struct  intel_ring_buffer {
                         struct drm_i915_gem_execbuffer2 *exec,
                         struct drm_clip_rect *cliprects,
                         uint64_t exec_offset);
+        void            (*cleanup)(struct intel_ring_buffer *ring);
 
         /**
          * List of objects currently involved in rendering from the
@@ -98,6 +99,8 @@ struct  intel_ring_buffer {
 
         wait_queue_head_t irq_queue;
         drm_local_map_t map;
+
+        void *private;
 };
 
 static inline u32