drm/i915: vblank status not valid while training display port

While the display port is in training mode, vblank interrupts don't
occur. Because we have to wait for the display port output to turn on
before starting the training sequence, enable the output in 'normal'
mode so that we can tell when a vblank has occurred, then start the
training sequence.
Signed-off-by: Keith Packard <keithp@keithp.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

drivers/gpu/drm/i915/intel_dp.c

@@ -1138,18 +1138,14 @@ static bool
 intel_dp_set_link_train(struct intel_dp *intel_dp,
 			uint32_t dp_reg_value,
 			uint8_t dp_train_pat,
-			uint8_t train_set[4],
-			bool first)
+			uint8_t train_set[4])
 {
 	struct drm_device *dev = intel_dp->base.enc.dev;
 	struct drm_i915_private *dev_priv = dev->dev_private;
-	struct intel_crtc *intel_crtc = to_intel_crtc(intel_dp->base.enc.crtc);
 	int ret;
 
 	I915_WRITE(intel_dp->output_reg, dp_reg_value);
 	POSTING_READ(intel_dp->output_reg);
-	if (first)
-		intel_wait_for_vblank(dev, intel_crtc->pipe);
 
 	intel_dp_aux_native_write_1(intel_dp,
 				    DP_TRAINING_PATTERN_SET,
@@ -1174,10 +1170,15 @@ intel_dp_link_train(struct intel_dp *intel_dp)
 	uint8_t voltage;
 	bool clock_recovery = false;
 	bool channel_eq = false;
-	bool first = true;
 	int tries;
 	u32 reg;
 	uint32_t DP = intel_dp->DP;
+	struct intel_crtc *intel_crtc = to_intel_crtc(intel_dp->base.enc.crtc);
+
+	/* Enable output, wait for it to become active */
+	I915_WRITE(intel_dp->output_reg, intel_dp->DP);
+	POSTING_READ(intel_dp->output_reg);
+	intel_wait_for_vblank(dev, intel_crtc->pipe);
 
 	/* Write the link configuration data */
 	intel_dp_aux_native_write(intel_dp, DP_LINK_BW_SET,
@@ -1210,9 +1211,8 @@ intel_dp_link_train(struct intel_dp *intel_dp)
 			reg = DP | DP_LINK_TRAIN_PAT_1;
 
 		if (!intel_dp_set_link_train(intel_dp, reg,
-					     DP_TRAINING_PATTERN_1, train_set, first))
+					     DP_TRAINING_PATTERN_1, train_set))
 			break;
-		first = false;
 		/* Set training pattern 1 */
 
 		udelay(100);
@@ -1266,8 +1266,7 @@ intel_dp_link_train(struct intel_dp *intel_dp)
 
 		/* channel eq pattern */
 		if (!intel_dp_set_link_train(intel_dp, reg,
-					     DP_TRAINING_PATTERN_2, train_set,
-					     false))
+					     DP_TRAINING_PATTERN_2, train_set))
 			break;
 
 		udelay(400);