drm/i915: Take runtime pm reference on hangcheck_info

We read the coherent current seqno and actual head from ring.
For hardware access we need to take runtime_pm reference.

Get hardware specific values with runtime reference held
and print them first to emphasize hw state vs bookkeepping.

v2: Reorder output according to hw access (Chris)
    remove superfluous locking (Daniel)

Testcase: igt/pm_rpm/debugfs-read
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=88910
Tested-by: Ding Heng <hengx.ding@intel.com> (v1)
Signed-off-by: Mika Kuoppala <mika.kuoppala@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>

drivers/gpu/drm/i915/i915_debugfs.c

@@ -1223,8 +1223,11 @@ static int i915_frequency_info(struct seq_file *m, void *unused)
 static int i915_hangcheck_info(struct seq_file *m, void *unused)
 {
 	struct drm_info_node *node = m->private;
-	struct drm_i915_private *dev_priv = to_i915(node->minor->dev);
+	struct drm_device *dev = node->minor->dev;
+	struct drm_i915_private *dev_priv = dev->dev_private;
 	struct intel_engine_cs *ring;
+	u64 acthd[I915_NUM_RINGS];
+	u32 seqno[I915_NUM_RINGS];
 	int i;
 
 	if (!i915.enable_hangcheck) {
@@ -1232,6 +1235,15 @@ static int i915_hangcheck_info(struct seq_file *m, void *unused)
 		return 0;
 	}
 
+	intel_runtime_pm_get(dev_priv);
+
+	for_each_ring(ring, dev_priv, i) {
+		seqno[i] = ring->get_seqno(ring, false);
+		acthd[i] = intel_ring_get_active_head(ring);
+	}
+
+	intel_runtime_pm_put(dev_priv);
+
 	if (delayed_work_pending(&dev_priv->gpu_error.hangcheck_work)) {
 		seq_printf(m, "Hangcheck active, fires in %dms\n",
 			   jiffies_to_msecs(dev_priv->gpu_error.hangcheck_work.timer.expires -
@@ -1242,14 +1254,14 @@ static int i915_hangcheck_info(struct seq_file *m, void *unused)
 	for_each_ring(ring, dev_priv, i) {
 		seq_printf(m, "%s:\n", ring->name);
 		seq_printf(m, "\tseqno = %x [current %x]\n",
-			   ring->hangcheck.seqno, ring->get_seqno(ring, false));
-		seq_printf(m, "\taction = %d\n", ring->hangcheck.action);
-		seq_printf(m, "\tscore = %d\n", ring->hangcheck.score);
+			   ring->hangcheck.seqno, seqno[i]);
 		seq_printf(m, "\tACTHD = 0x%08llx [current 0x%08llx]\n",
 			   (long long)ring->hangcheck.acthd,
-			   (long long)intel_ring_get_active_head(ring));
+			   (long long)acthd[i]);
 		seq_printf(m, "\tmax ACTHD = 0x%08llx\n",
 			   (long long)ring->hangcheck.max_acthd);
+		seq_printf(m, "\tscore = %d\n", ring->hangcheck.score);
+		seq_printf(m, "\taction = %d\n", ring->hangcheck.action);
 	}
 
 	return 0;