1 files changed, 35 insertions, 2 deletions

diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index a31ee3202f17..94b9bdce0c75 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -2350,6 +2350,7 @@ i915_gem_init_ringbuffer(struct drm_device *dev)
         struct drm_gem_object *obj;
         struct drm_i915_gem_object *obj_priv;
         int ret;
+        u32 head;
 
         ret = i915_gem_init_hws(dev);
         if (ret != 0)
@@ -2390,17 +2391,49 @@ i915_gem_init_ringbuffer(struct drm_device *dev)
 
         /* Stop the ring if it's running. */
         I915_WRITE(PRB0_CTL, 0);
-        I915_WRITE(PRB0_HEAD, 0);
         I915_WRITE(PRB0_TAIL, 0);
-        I915_WRITE(PRB0_START, 0);
+        I915_WRITE(PRB0_HEAD, 0);
 
         /* Initialize the ring. */
         I915_WRITE(PRB0_START, obj_priv->gtt_offset);
+        head = I915_READ(PRB0_HEAD) & HEAD_ADDR;
+
+        /* G45 ring initialization fails to reset head to zero */
+        if (head != 0) {
+                DRM_ERROR("Ring head not reset to zero "
+                          "ctl %08x head %08x tail %08x start %08x\n",
+                          I915_READ(PRB0_CTL),
+                          I915_READ(PRB0_HEAD),
+                          I915_READ(PRB0_TAIL),
+                          I915_READ(PRB0_START));
+                I915_WRITE(PRB0_HEAD, 0);
+
+                DRM_ERROR("Ring head forced to zero "
+                          "ctl %08x head %08x tail %08x start %08x\n",
+                          I915_READ(PRB0_CTL),
+                          I915_READ(PRB0_HEAD),
+                          I915_READ(PRB0_TAIL),
+                          I915_READ(PRB0_START));
+        }
+
         I915_WRITE(PRB0_CTL,
                    ((obj->size - 4096) & RING_NR_PAGES) |
                    RING_NO_REPORT |
                    RING_VALID);
 
+        head = I915_READ(PRB0_HEAD) & HEAD_ADDR;
+
+        /* If the head is still not zero, the ring is dead */
+        if (head != 0) {
+                DRM_ERROR("Ring initialization failed "
+                          "ctl %08x head %08x tail %08x start %08x\n",
+                          I915_READ(PRB0_CTL),
+                          I915_READ(PRB0_HEAD),
+                          I915_READ(PRB0_TAIL),
+                          I915_READ(PRB0_START));
+                return -EIO;
+        }
+
         /* Update our cache of the ring state */
         i915_kernel_lost_context(dev);