[PATCH] drivers/i915: Fix unnoticed failure of init_ring_common()

[Konrad Zapalowicz <bergo.torino@gmail.com>]

This commit add check for return value of init_ring_common() in the
init_render_ring(). Now, when failure is detected the error code is
propagated to the caller layer instead of being ignored.

I believe that this fix will have a positive impact on the oops that
I hit recently and which starts when init_ring_common() fails:

    [drm:init_ring_common] *ERROR* render ring initialization failed
             ctl 0001f001 head 0000000c tail 00000000 start 003eb000
    BUG: unable to handle kernel NULL pointer dereference at 0000006c
    IP: [<f8ca1679>] i915_gem_obj_to_ggtt+0x9/0x40 [i915]

Signed-off-by: Konrad Zapalowicz <bergo.torino@gmail.com>
---
 drivers/gpu/drm/i915/intel_ringbuffer.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
index 279488a..d205b0d 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.c
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
@@ -604,6 +604,8 @@ static int init_render_ring(struct intel_engine_cs *ring)
 	struct drm_device *dev = ring->dev;
 	struct drm_i915_private *dev_priv = dev->dev_private;
 	int ret = init_ring_common(ring);
+	if (ret)
+		return ret;
 
 	/* WaTimedSingleVertexDispatch:cl,bw,ctg,elk,ilk,snb */
 	if (INTEL_INFO(dev)->gen >= 4 && INTEL_INFO(dev)->gen < 7)
-- 
1.8.1.2