drm/i915: fix hsw_fdi_link_train "retry" code

We were previously doing exactly what the "mode set sequence for CRT"
document mandates, but whenever we failed to train the link in the
first tentative, all the other subsequent retries always failed. In
one of my monitors that has 47 modes, I was usually getting around 3
failures when running "testdisplay -a".

After this patch, even if we fail in the first tentative, we can
succeed in the next ones. So now when running "testdisplay -a" I see
around 3 times the message "FDI link training done on step 1" and no
failures.

Notice that now the "retry" code looks a lot like the DP retry code.
Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_ddi.c

@@ -138,6 +138,19 @@ static const long hsw_ddi_buf_ctl_values[] = {
 	DDI_BUF_EMP_800MV_3_5DB_HSW
 };
 
+static void intel_wait_ddi_buf_idle(struct drm_i915_private *dev_priv,
+				    enum port port)
+{
+	uint32_t reg = DDI_BUF_CTL(port);
+	int i;
+
+	for (i = 0; i < 8; i++) {
+		udelay(1);
+		if (I915_READ(reg) & DDI_BUF_IS_IDLE)
+			return;
+	}
+	DRM_ERROR("Timeout waiting for DDI BUF %c idle bit\n", port_name(port));
+}
 
 /* Starting with Haswell, different DDI ports can work in FDI mode for
  * connection to the PCH-located connectors. For this, it is necessary to train
@@ -231,18 +244,30 @@ void hsw_fdi_link_train(struct drm_crtc *crtc)
 			return;
 		}
 
+		temp = I915_READ(DDI_BUF_CTL(PORT_E));
+		temp &= ~DDI_BUF_CTL_ENABLE;
+		I915_WRITE(DDI_BUF_CTL(PORT_E), temp);
+		POSTING_READ(DDI_BUF_CTL(PORT_E));
+
 		/* Disable DP_TP_CTL and FDI_RX_CTL and retry */
-		I915_WRITE(DP_TP_CTL(PORT_E),
-			   I915_READ(DP_TP_CTL(PORT_E)) & ~DP_TP_CTL_ENABLE);
+		temp = I915_READ(DP_TP_CTL(PORT_E));
+		temp &= ~(DP_TP_CTL_ENABLE | DP_TP_CTL_LINK_TRAIN_MASK);
+		temp |= DP_TP_CTL_LINK_TRAIN_PAT1;
+		I915_WRITE(DP_TP_CTL(PORT_E), temp);
+		POSTING_READ(DP_TP_CTL(PORT_E));
+
+		intel_wait_ddi_buf_idle(dev_priv, PORT_E);
 
 		rx_ctl_val &= ~FDI_RX_ENABLE;
 		I915_WRITE(_FDI_RXA_CTL, rx_ctl_val);
+		POSTING_READ(_FDI_RXA_CTL);
 
 		/* Reset FDI_RX_MISC pwrdn lanes */
 		temp = I915_READ(_FDI_RXA_MISC);
 		temp &= ~(FDI_RX_PWRDN_LANE1_MASK | FDI_RX_PWRDN_LANE0_MASK);
 		temp |= FDI_RX_PWRDN_LANE1_VAL(2) | FDI_RX_PWRDN_LANE0_VAL(2);
 		I915_WRITE(_FDI_RXA_MISC, temp);
+		POSTING_READ(_FDI_RXA_MISC);
 	}
 
 	DRM_ERROR("FDI link training failed!\n");
@@ -1222,20 +1247,6 @@ static void intel_ddi_pre_enable(struct intel_encoder *intel_encoder)
 	}
 }
 
-static void intel_wait_ddi_buf_idle(struct drm_i915_private *dev_priv,
-				    enum port port)
-{
-	uint32_t reg = DDI_BUF_CTL(port);
-	int i;
-
-	for (i = 0; i < 8; i++) {
-		udelay(1);
-		if (I915_READ(reg) & DDI_BUF_IS_IDLE)
-			return;
-	}
-	DRM_ERROR("Timeout waiting for DDI BUF %c idle bit\n", port_name(port));
-}
-
 static void intel_ddi_post_disable(struct intel_encoder *intel_encoder)
 {
 	struct drm_encoder *encoder = &intel_encoder->base;