drm/i915: Record the position of the request upon error

So that we can tally the request against the command sequence in the
ringbuffer, or merely jump to the interesting locations.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_debugfs.c

@@ -799,9 +799,10 @@ static int i915_error_state(struct seq_file *m, void *unused)
 				   dev_priv->ring[i].name,
 				   error->ring[i].num_requests);
 			for (j = 0; j < error->ring[i].num_requests; j++) {
-				seq_printf(m, "  seqno 0x%08x, emitted %ld\n",
+				seq_printf(m, "  seqno 0x%08x, emitted %ld, tail 0x%08x\n",
 					   error->ring[i].requests[j].seqno,
-					   error->ring[i].requests[j].jiffies);
+					   error->ring[i].requests[j].jiffies,
+					   error->ring[i].requests[j].tail);
 			}
 		}
 

drivers/gpu/drm/i915/i915_drv.h

@@ -183,6 +183,7 @@ struct drm_i915_error_state {
 		struct drm_i915_error_request {
 			long jiffies;
 			u32 seqno;
+			u32 tail;
 		} *requests;
 		int num_requests;
 	} ring[I915_NUM_RINGS];

drivers/gpu/drm/i915/i915_irq.c

@@ -975,6 +975,7 @@ static void i915_gem_record_rings(struct drm_device *dev,
 			erq = &error->ring[i].requests[count++];
 			erq->seqno = request->seqno;
 			erq->jiffies = request->emitted_jiffies;
+			erq->tail = request->tail;
 		}
 	}
 }