drm/i915: Handle locking better in i915_sink_crc.

Lock the bare minimum, instead of the entire world, and
use interruptible locking because we can.
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171110113503.16253-6-maarten.lankhorst@linux.intel.comReviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_debugfs.c

@@ -2735,39 +2735,63 @@ static int i915_sink_crc(struct seq_file *m, void *data)
 	struct intel_connector *connector;
 	struct drm_connector_list_iter conn_iter;
 	struct intel_dp *intel_dp = NULL;
+	struct drm_modeset_acquire_ctx ctx;
 	int ret;
 	u8 crc[6];
 
-	drm_modeset_lock_all(dev);
+	drm_modeset_acquire_init(&ctx, DRM_MODESET_ACQUIRE_INTERRUPTIBLE);
+
 	drm_connector_list_iter_begin(dev, &conn_iter);
+
 	for_each_intel_connector_iter(connector, &conn_iter) {
 		struct drm_crtc *crtc;
+		struct drm_connector_state *state;
 
-		if (!connector->base.state->best_encoder)
+		if (connector->base.connector_type != DRM_MODE_CONNECTOR_eDP)
 			continue;
 
-		crtc = connector->base.state->crtc;
-		if (!crtc->state->active)
+retry:
+		ret = drm_modeset_lock(&dev->mode_config.connection_mutex, &ctx);
+		if (ret)
+			goto err;
+
+		state = connector->base.state;
+		if (!state->best_encoder)
 			continue;
 
-		if (connector->base.connector_type != DRM_MODE_CONNECTOR_eDP)
+		crtc = state->crtc;
+		ret = drm_modeset_lock(&crtc->mutex, &ctx);
+		if (ret)
+			goto err;
+
+		if (!crtc->state->active)
 			continue;
 
-		intel_dp = enc_to_intel_dp(connector->base.state->best_encoder);
+		intel_dp = enc_to_intel_dp(state->best_encoder);
 
 		ret = intel_dp_sink_crc(intel_dp, crc);
 		if (ret)
-			goto out;
+			goto err;
 
 		seq_printf(m, "%02x%02x%02x%02x%02x%02x\n",
 			   crc[0], crc[1], crc[2],
 			   crc[3], crc[4], crc[5]);
 		goto out;
+
+err:
+		if (ret == -EDEADLK) {
+			ret = drm_modeset_backoff(&ctx);
+			if (!ret)
+				goto retry;
+		}
+		goto out;
 	}
 	ret = -ENODEV;
 out:
 	drm_connector_list_iter_end(&conn_iter);
-	drm_modeset_unlock_all(dev);
+	drm_modeset_drop_locks(&ctx);
+	drm_modeset_acquire_fini(&ctx);
+
 	return ret;
 }