drm/i915: Show bounds of active request in the ring on GPU hang

Include the position of the active request in the ring, and display that
alongside the current RING registers (on a GPU hang).

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20161004201132.21801-6-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_drv.h

@@ -788,6 +788,9 @@ struct drm_i915_error_state {
 		struct i915_address_space *vm;
 		int num_requests;
 
+		/* position of active request inside the ring */
+		u32 rq_head, rq_post, rq_tail;
+
 		/* our own tracking of ring head and tail */
 		u32 cpu_ring_head;
 		u32 cpu_ring_tail;

drivers/gpu/drm/i915/i915_gpu_error.c

@@ -262,8 +262,9 @@ static void error_print_engine(struct drm_i915_error_state_buf *m,
 {
 	err_printf(m, "%s command stream:\n", engine_str(ee->engine_id));
 	err_printf(m, "  START: 0x%08x\n", ee->start);
-	err_printf(m, "  HEAD:  0x%08x\n", ee->head);
-	err_printf(m, "  TAIL:  0x%08x\n", ee->tail);
+	err_printf(m, "  HEAD:  0x%08x\n [0x%08x]", ee->head, ee->rq_head);
+	err_printf(m, "  TAIL:  0x%08x [0x%08x, 0x%08x]\n",
+		   ee->tail, ee->rq_post, ee->rq_tail);
 	err_printf(m, "  CTL:   0x%08x\n", ee->ctl);
 	err_printf(m, "  MODE:  0x%08x\n", ee->mode);
 	err_printf(m, "  HWS:   0x%08x\n", ee->hws);
@@ -1230,6 +1231,10 @@ static void i915_gem_record_rings(struct drm_i915_private *dev_priv,
 			error->simulated |=
 				request->ctx->flags & CONTEXT_NO_ERROR_CAPTURE;
 
+			ee->rq_head = request->head;
+			ee->rq_post = request->postfix;
+			ee->rq_tail = request->tail;
+
 			ring = request->ring;
 			ee->cpu_ring_head = ring->head;
 			ee->cpu_ring_tail = ring->tail;