drm/i915: hsw: fix link training for eDP on port-A

According to BSpec the link training sequence for eDP on HSW port-A
should be as follows:

1. link training: clock recovery
2. link training: equalization
3. link training: set idle transmission mode
4. display pipe enable
5. link training: disable (set normal mode)

Contrary to this at the moment we don't do step 3. and we do step 5.
before step 4. Fix this by setting idle transmission mode for eDP at
the end of intel_dp_complete_link_train and adding a new
intel_dp_stop_link_training function to disable link training. With
these changes we'll end up with the following functions corresponding
to the above steps:

intel_dp_start_link_train    -> step 1.
intel_dp_complete_link_train -> step 2., step 3.
intel_dp_stop_link_train     -> step 5.

For port-A we'll call intel_dp_stop_link_train only after enabling the
pipe, for everything else we'll call it right after
intel_dp_complete_link_train to preserve the current behavior.

Tested on HSW/HSW-ULT.

In v2:
- Due to a HW issue we must set idle transmission mode for port-A too
  before enabling the pipe. Thanks for Arthur Runyan for explaining
  this.
- Update the patch subject to make it clear that it's an eDP fix, DP is
  not affected.

v3:
- rename intel_dp_link_train() to intel_dp_set_link_train(), use 'val'
  instead 'l' as var name. (Paulo)
Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Tested-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_ddi.c

@@ -1265,6 +1265,8 @@ static void intel_ddi_pre_enable(struct intel_encoder *intel_encoder)
 		intel_dp_sink_dpms(intel_dp, DRM_MODE_DPMS_ON);
 		intel_dp_start_link_train(intel_dp);
 		intel_dp_complete_link_train(intel_dp);
+		if (port != PORT_A)
+			intel_dp_stop_link_train(intel_dp);
 	}
 }
 
@@ -1326,6 +1328,9 @@ static void intel_enable_ddi(struct intel_encoder *intel_encoder)
 	} else if (type == INTEL_OUTPUT_EDP) {
 		struct intel_dp *intel_dp = enc_to_intel_dp(encoder);
 
+		if (port == PORT_A)
+			intel_dp_stop_link_train(intel_dp);
+
 		ironlake_edp_backlight_on(intel_dp);
 	}
 

drivers/gpu/drm/i915/intel_dp.c

@@ -1379,6 +1379,7 @@ static void intel_enable_dp(struct intel_encoder *encoder)
 	ironlake_edp_panel_on(intel_dp);
 	ironlake_edp_panel_vdd_off(intel_dp, true);
 	intel_dp_complete_link_train(intel_dp);
+	intel_dp_stop_link_train(intel_dp);
 	ironlake_edp_backlight_on(intel_dp);
 }
 
@@ -1701,10 +1702,9 @@ intel_dp_set_link_train(struct intel_dp *intel_dp,
 	struct drm_i915_private *dev_priv = dev->dev_private;
 	enum port port = intel_dig_port->port;
 	int ret;
-	uint32_t temp;
 
 	if (HAS_DDI(dev)) {
-		temp = I915_READ(DP_TP_CTL(port));
+		uint32_t temp = I915_READ(DP_TP_CTL(port));
 
 		if (dp_train_pat & DP_LINK_SCRAMBLING_DISABLE)
 			temp |= DP_TP_CTL_SCRAMBLE_DISABLE;
@@ -1714,18 +1714,6 @@ intel_dp_set_link_train(struct intel_dp *intel_dp,
 		temp &= ~DP_TP_CTL_LINK_TRAIN_MASK;
 		switch (dp_train_pat & DP_TRAINING_PATTERN_MASK) {
 		case DP_TRAINING_PATTERN_DISABLE:
-
-			if (port != PORT_A) {
-				temp |= DP_TP_CTL_LINK_TRAIN_IDLE;
-				I915_WRITE(DP_TP_CTL(port), temp);
-
-				if (wait_for((I915_READ(DP_TP_STATUS(port)) &
-					      DP_TP_STATUS_IDLE_DONE), 1))
-					DRM_ERROR("Timed out waiting for DP idle patterns\n");
-
-				temp &= ~DP_TP_CTL_LINK_TRAIN_MASK;
-			}
-
 			temp |= DP_TP_CTL_LINK_TRAIN_NORMAL;
 
 			break;
@@ -1801,6 +1789,37 @@ intel_dp_set_link_train(struct intel_dp *intel_dp,
 	return true;
 }
 
+static void intel_dp_set_idle_link_train(struct intel_dp *intel_dp)
+{
+	struct intel_digital_port *intel_dig_port = dp_to_dig_port(intel_dp);
+	struct drm_device *dev = intel_dig_port->base.base.dev;
+	struct drm_i915_private *dev_priv = dev->dev_private;
+	enum port port = intel_dig_port->port;
+	uint32_t val;
+
+	if (!HAS_DDI(dev))
+		return;
+
+	val = I915_READ(DP_TP_CTL(port));
+	val &= ~DP_TP_CTL_LINK_TRAIN_MASK;
+	val |= DP_TP_CTL_LINK_TRAIN_IDLE;
+	I915_WRITE(DP_TP_CTL(port), val);
+
+	/*
+	 * On PORT_A we can have only eDP in SST mode. There the only reason
+	 * we need to set idle transmission mode is to work around a HW issue
+	 * where we enable the pipe while not in idle link-training mode.
+	 * In this case there is requirement to wait for a minimum number of
+	 * idle patterns to be sent.
+	 */
+	if (port == PORT_A)
+		return;
+
+	if (wait_for((I915_READ(DP_TP_STATUS(port)) & DP_TP_STATUS_IDLE_DONE),
+		     1))
+		DRM_ERROR("Timed out waiting for DP idle patterns\n");
+}
+
 /* Enable corresponding port and start training pattern 1 */
 void
 intel_dp_start_link_train(struct intel_dp *intel_dp)
@@ -1943,10 +1962,19 @@ intel_dp_complete_link_train(struct intel_dp *intel_dp)
 		++tries;
 	}
 
+	intel_dp_set_idle_link_train(intel_dp);
+
+	intel_dp->DP = DP;
+
 	if (channel_eq)
 		DRM_DEBUG_KMS("Channel EQ done. DP Training successfull\n");
 
-	intel_dp_set_link_train(intel_dp, DP, DP_TRAINING_PATTERN_DISABLE);
+}
+
+void intel_dp_stop_link_train(struct intel_dp *intel_dp)
+{
+	intel_dp_set_link_train(intel_dp, intel_dp->DP,
+				DP_TRAINING_PATTERN_DISABLE);
 }
 
 static void
@@ -2154,6 +2182,7 @@ intel_dp_check_link_status(struct intel_dp *intel_dp)
 			      drm_get_encoder_name(&intel_encoder->base));
 		intel_dp_start_link_train(intel_dp);
 		intel_dp_complete_link_train(intel_dp);
+		intel_dp_stop_link_train(intel_dp);
 	}
 }
 

drivers/gpu/drm/i915/intel_drv.h

@@ -499,6 +499,7 @@ extern void intel_dp_init_connector(struct intel_digital_port *intel_dig_port,
 extern void intel_dp_init_link_config(struct intel_dp *intel_dp);
 extern void intel_dp_start_link_train(struct intel_dp *intel_dp);
 extern void intel_dp_complete_link_train(struct intel_dp *intel_dp);
+extern void intel_dp_stop_link_train(struct intel_dp *intel_dp);
 extern void intel_dp_sink_dpms(struct intel_dp *intel_dp, int mode);
 extern void intel_dp_encoder_destroy(struct drm_encoder *encoder);
 extern void intel_dp_check_link_status(struct intel_dp *intel_dp);