drm/i915: make DP training try a little harder

When trying to do channel equalization, we need to make sure we still
have clock recovery on all lanes while training.  We also need to try
clock recovery again if we lose the clock or if channel eq fails 5
times.  We'll try clock recovery up to 5 more times before giving up
entirely.

Gets suspend/resume working on my Vaio again and brings us back into
compliance with the DP training sequence spec.
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

drivers/gpu/drm/i915/intel_dp.c

@@ -1334,17 +1334,24 @@ intel_dp_complete_link_train(struct intel_dp *intel_dp)
 	struct drm_device *dev = intel_dp->base.base.dev;
 	struct drm_i915_private *dev_priv = dev->dev_private;
 	bool channel_eq = false;
-	int tries;
+	int tries, cr_tries;
 	u32 reg;
 	uint32_t DP = intel_dp->DP;
 
 	/* channel equalization */
 	tries = 0;
+	cr_tries = 0;
 	channel_eq = false;
 	for (;;) {
 		/* Use intel_dp->train_set[0] to set the voltage and pre emphasis values */
 		uint32_t    signal_levels;
 
+		if (cr_tries > 5) {
+			DRM_ERROR("failed to train DP, aborting\n");
+			intel_dp_link_down(intel_dp);
+			break;
+		}
+
 		if (IS_GEN6(dev) && is_edp(intel_dp)) {
 			signal_levels = intel_gen6_edp_signal_levels(intel_dp->train_set[0]);
 			DP = (DP & ~EDP_LINK_TRAIN_VOL_EMP_MASK_SNB) | signal_levels;
@@ -1367,14 +1374,26 @@ intel_dp_complete_link_train(struct intel_dp *intel_dp)
 		if (!intel_dp_get_link_status(intel_dp))
 			break;
 
+		/* Make sure clock is still ok */
+		if (!intel_clock_recovery_ok(intel_dp->link_status, intel_dp->lane_count)) {
+			intel_dp_start_link_train(intel_dp);
+			cr_tries++;
+			continue;
+		}
+
 		if (intel_channel_eq_ok(intel_dp)) {
 			channel_eq = true;
 			break;
 		}
 
-		/* Try 5 times */
-		if (tries > 5)
-			break;
+		/* Try 5 times, then try clock recovery if that fails */
+		if (tries > 5) {
+			intel_dp_link_down(intel_dp);
+			intel_dp_start_link_train(intel_dp);
+			tries = 0;
+			cr_tries++;
+			continue;
+		}
 
 		/* Compute new intel_dp->train_set as requested by target */
 		intel_get_adjust_train(intel_dp);