[PATCH 2/3] drm/i915: Wait for pending modesets to complete before trying link training

[Maarten Lankhorst]

We're protected by the connection_mutex lock against blocking modesets,
but nonblocking modesets are performed without any locking. This is
causing WARN in drm_wait_for_vblank and in general it's better to wait
before modeset completes before trying anything.

Signed-off-by: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>
---
 drivers/gpu/drm/i915/intel_dp.c | 51 +++++++++++++++++++++++++++++++----------
 1 file changed, 39 insertions(+), 12 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index fb12896bafee..71882d887393 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -4080,24 +4080,38 @@ intel_dp_check_link_status(struct intel_dp *intel_dp)
 	struct intel_encoder *intel_encoder = &dp_to_dig_port(intel_dp)->base;
 	struct drm_device *dev = intel_dp_to_dev(intel_dp);
 	u8 link_status[DP_LINK_STATUS_SIZE];
+	struct drm_modeset_acquire_ctx ctx;
+	struct intel_connector *intel_connector = intel_dp->attached_connector;
+	int ret;
+	struct drm_crtc *crtc;
 
-	WARN_ON(!drm_modeset_is_locked(&dev->mode_config.connection_mutex));
+	drm_modeset_acquire_init(&ctx, 0);
+
+retry:
+	ret = drm_modeset_lock(&dev->mode_config.connection_mutex, &ctx);
+	if (ret)
+		goto out;
 
 	if (!intel_dp_get_link_status(intel_dp, link_status)) {
 		DRM_ERROR("Failed to get link status\n");
-		return;
+		goto out;
 	}
 
-	if (!intel_encoder->base.crtc)
-		return;
+	crtc = intel_connector->base.state->crtc;
+	if (!crtc)
+		goto out;
 
-	if (!to_intel_crtc(intel_encoder->base.crtc)->active)
-		return;
+	ret = drm_modeset_lock(&crtc->mutex, &ctx);
+	if (ret)
+		goto out;
+
+	if (!crtc->state->active)
+		goto out;
 
 	/* FIXME: we need to synchronize this sort of stuff with hardware
 	 * readout. Currently fast link training doesn't work on boot-up. */
 	if (!intel_dp->lane_count)
-		return;
+		goto out;
 
 	/* if link training is requested we should perform it always */
 	if ((intel_dp->compliance.test_type == DP_TEST_LINK_TRAINING) ||
@@ -4105,8 +4119,26 @@ intel_dp_check_link_status(struct intel_dp *intel_dp)
 		DRM_DEBUG_KMS("%s: channel EQ not ok, retraining\n",
 			      intel_encoder->base.name);
 
+		if (drm_atomic_crtc_needs_modeset(crtc->state)) {
+			/* wait for atomic modeset to complete */
+			ret = drm_atomic_helper_wait_for_hw_done(crtc);
+			if (ret < 0)
+				DRM_ERROR("Waiting for hw_done timed out\n");
+		}
+
 		intel_dp_retrain_link(intel_dp);
 	}
+
+out:
+	if (ret == -EDEADLK) {
+		drm_modeset_backoff(&ctx);
+		goto retry;
+	}
+
+	drm_modeset_drop_locks(&ctx);
+	drm_modeset_acquire_fini(&ctx);
+	if (ret)
+		DRM_ERROR("Locking failed with %i\n", ret);
 }
 
 /*
@@ -4125,7 +4157,6 @@ intel_dp_check_link_status(struct intel_dp *intel_dp)
 static bool
 intel_dp_short_pulse(struct intel_dp *intel_dp)
 {
-	struct drm_device *dev = intel_dp_to_dev(intel_dp);
 	u8 sink_irq_vector = 0;
 	u8 old_sink_count = intel_dp->sink_count;
 	bool ret;
@@ -4164,9 +4195,7 @@ intel_dp_short_pulse(struct intel_dp *intel_dp)
 			DRM_DEBUG_DRIVER("CP or sink specific irq unhandled\n");
 	}
 
-	drm_modeset_lock(&dev->mode_config.connection_mutex, NULL);
 	intel_dp_check_link_status(intel_dp);
-	drm_modeset_unlock(&dev->mode_config.connection_mutex);
 
 	return true;
 }
@@ -4499,9 +4528,7 @@ intel_dp_long_pulse(struct intel_connector *intel_connector)
 		 * check links status, there has been known issues of
 		 * link loss triggerring long pulse!!!!
 		 */
-		drm_modeset_lock(&dev->mode_config.connection_mutex, NULL);
 		intel_dp_check_link_status(intel_dp);
-		drm_modeset_unlock(&dev->mode_config.connection_mutex);
 		goto out;
 	}
 
-- 
2.7.4