drm/i915: Dump the ringbuffer of the active request for debugging

Sometimes we need to see what instructions we emitted for a request to
try and gather a glimmer of insight into what the GPU is doing when it
stops responding.

v2: Move ring dumping into its own routine

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20180614122150.17552-1-chris@chris-wilson.co.uk
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>

drivers/gpu/drm/i915/intel_engine_cs.c

@@ -1394,6 +1394,39 @@ static void intel_engine_print_registers(const struct intel_engine_cs *engine,
 	}
 }
 
+static void print_request_ring(struct drm_printer *m, struct i915_request *rq)
+{
+	void *ring;
+	int size;
+
+	drm_printf(m,
+		   "[head %04x, postfix %04x, tail %04x, batch 0x%08x_%08x]:\n",
+		   rq->head, rq->postfix, rq->tail,
+		   rq->batch ? upper_32_bits(rq->batch->node.start) : ~0u,
+		   rq->batch ? lower_32_bits(rq->batch->node.start) : ~0u);
+
+	size = rq->tail - rq->head;
+	if (rq->tail < rq->head)
+		size += rq->ring->size;
+
+	ring = kmalloc(size, GFP_ATOMIC);
+	if (ring) {
+		const void *vaddr = rq->ring->vaddr;
+		unsigned int head = rq->head;
+		unsigned int len = 0;
+
+		if (rq->tail < head) {
+			len = rq->ring->size - head;
+			memcpy(ring, vaddr + head, len);
+			head = 0;
+		}
+		memcpy(ring + len, vaddr + head, size - len);
+
+		hexdump(m, ring, size);
+		kfree(ring);
+	}
+}
+
 void intel_engine_dump(struct intel_engine_cs *engine,
 		       struct drm_printer *m,
 		       const char *header, ...)
@@ -1444,11 +1477,7 @@ void intel_engine_dump(struct intel_engine_cs *engine,
 	rq = i915_gem_find_active_request(engine);
 	if (rq) {
 		print_request(m, rq, "\t\tactive ");
-		drm_printf(m,
-			   "\t\t[head %04x, postfix %04x, tail %04x, batch 0x%08x_%08x]\n",
-			   rq->head, rq->postfix, rq->tail,
-			   rq->batch ? upper_32_bits(rq->batch->node.start) : ~0u,
-			   rq->batch ? lower_32_bits(rq->batch->node.start) : ~0u);
+
 		drm_printf(m, "\t\tring->start:  0x%08x\n",
 			   i915_ggtt_offset(rq->ring->vma));
 		drm_printf(m, "\t\tring->head:   0x%08x\n",
@@ -1459,6 +1488,8 @@ void intel_engine_dump(struct intel_engine_cs *engine,
 			   rq->ring->emit);
 		drm_printf(m, "\t\tring->space:  0x%08x\n",
 			   rq->ring->space);
+
+		print_request_ring(m, rq);
 	}
 
 	rcu_read_unlock();