drm/i915: Show ring->start for the ELSP context/request queue

Since the advent of execlists, the HW no longer executes from a single
statically assigned ring, but instead switches to a different ring for
each context (logical ringbuffer contexts as it is called). So a good way
to tally the executing context against what we have queued is by
comparing the RING_START register against our requests. Make it so.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180502104150.29874-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_gpu_error.c

@@ -410,11 +410,11 @@ static void error_print_request(struct drm_i915_error_state_buf *m,
 	if (!erq->seqno)
 		return;
 
-	err_printf(m, "%s pid %d, ban score %d, seqno %8x:%08x, prio %d, emitted %dms, head %08x, tail %08x\n",
+	err_printf(m, "%s pid %d, ban score %d, seqno %8x:%08x, prio %d, emitted %dms, start %08x, head %08x, tail %08x\n",
 		   prefix, erq->pid, erq->ban_score,
 		   erq->context, erq->seqno, erq->sched_attr.priority,
 		   jiffies_to_msecs(erq->jiffies - epoch),
-		   erq->head, erq->tail);
+		   erq->start, erq->head, erq->tail);
 }
 
 static void error_print_context(struct drm_i915_error_state_buf *m,
@@ -1292,6 +1292,7 @@ static void record_request(struct i915_request *request,
 	erq->ban_score = atomic_read(&request->ctx->ban_score);
 	erq->seqno = request->global_seqno;
 	erq->jiffies = request->emitted_jiffies;
+	erq->start = i915_ggtt_offset(request->ring->vma);
 	erq->head = request->head;
 	erq->tail = request->tail;
 

drivers/gpu/drm/i915/i915_gpu_error.h

@@ -152,6 +152,7 @@ struct i915_gpu_state {
 			u32 context;
 			int ban_score;
 			u32 seqno;
+			u32 start;
 			u32 head;
 			u32 tail;
 			struct i915_sched_attr sched_attr;

drivers/gpu/drm/i915/intel_engine_cs.c

@@ -1278,8 +1278,9 @@ static void intel_engine_print_registers(const struct intel_engine_cs *engine,
 				char hdr[80];
 
 				snprintf(hdr, sizeof(hdr),
-					 "\t\tELSP[%d] count=%d, rq: ",
-					 idx, count);
+					 "\t\tELSP[%d] count=%d, ring->start=%08x, rq: ",
+					 idx, count,
+					 i915_ggtt_offset(rq->ring->vma));
 				print_request(m, rq, hdr);
 			} else {
 				drm_printf(m, "\t\tELSP[%d] idle\n", idx);