drm/i915: Replace ILK eDP underrun suppression with something better

The underruns we were seeing when enabling eDP port A on ILK seem to
have been caused by prematurely clearing the LP1+ watermark values when
disabling LP1+ watermarks. Now that the watermarks are handled
properly, we can rip out the underrun suppression around the port A
enable.

We still need to worry about the underruns on FDI when enabling
the eDP PLL. But as Bspec tells us, we can avoid that by a vblank
wait on the pipe driving FDI just prior to enabling the eDP PLL.

Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: NVille Syrjälä <ville.syrjala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1459536799-18109-4-git-send-email-ville.syrjala@linux.intel.comReviewed-by: NPatrik Jakobsson <patrik.jakobsson@linux.intel.com>

drivers/gpu/drm/i915/intel_dp.c

@@ -2215,6 +2215,15 @@ static void ironlake_edp_pll_on(struct intel_dp *intel_dp)
 	POSTING_READ(DP_A);
 	udelay(500);
 
+	/*
+	 * [DevILK] Work around required when enabling DP PLL
+	 * while a pipe is enabled going to FDI:
+	 * 1. Wait for the start of vertical blank on the enabled pipe going to FDI
+	 * 2. Program DP PLL enable
+	 */
+	if (IS_GEN5(dev_priv))
+		intel_wait_for_vblank_if_active(dev_priv->dev, !crtc->pipe);
+
 	intel_dp->DP |= DP_PLL_ENABLE;
 
 	I915_WRITE(DP_A, intel_dp->DP);
@@ -2630,7 +2639,6 @@ static void intel_enable_dp(struct intel_encoder *encoder)
 	struct drm_i915_private *dev_priv = dev->dev_private;
 	struct intel_crtc *crtc = to_intel_crtc(encoder->base.crtc);
 	uint32_t dp_reg = I915_READ(intel_dp->output_reg);
-	enum port port = dp_to_dig_port(intel_dp)->port;
 	enum pipe pipe = crtc->pipe;
 
 	if (WARN_ON(dp_reg & DP_PORT_EN))
@@ -2643,17 +2651,6 @@ static void intel_enable_dp(struct intel_encoder *encoder)
 
 	intel_dp_enable_port(intel_dp);
 
-	if (port == PORT_A && IS_GEN5(dev_priv)) {
-		/*
-		 * Underrun reporting for the other pipe was disabled in
-		 * g4x_pre_enable_dp(). The eDP PLL and port have now been
-		 * enabled, so it's now safe to re-enable underrun reporting.
-		 */
-		intel_wait_for_vblank_if_active(dev_priv->dev, !pipe);
-		intel_set_cpu_fifo_underrun_reporting(dev_priv, !pipe, true);
-		intel_set_pch_fifo_underrun_reporting(dev_priv, !pipe, true);
-	}
-
 	edp_panel_vdd_on(intel_dp);
 	edp_panel_on(intel_dp);
 	edp_panel_vdd_off(intel_dp, true);
@@ -2699,26 +2696,11 @@ static void vlv_enable_dp(struct intel_encoder *encoder)
 
 static void g4x_pre_enable_dp(struct intel_encoder *encoder)
 {
-	struct drm_i915_private *dev_priv = to_i915(encoder->base.dev);
 	struct intel_dp *intel_dp = enc_to_intel_dp(&encoder->base);
 	enum port port = dp_to_dig_port(intel_dp)->port;
-	enum pipe pipe = to_intel_crtc(encoder->base.crtc)->pipe;
 
 	intel_dp_prepare(encoder);
 
-	if (port == PORT_A && IS_GEN5(dev_priv)) {
-		/*
-		 * We get FIFO underruns on the other pipe when
-		 * enabling the CPU eDP PLL, and when enabling CPU
-		 * eDP port. We could potentially avoid the PLL
-		 * underrun with a vblank wait just prior to enabling
-		 * the PLL, but that doesn't appear to help the port
-		 * enable case. Just sweep it all under the rug.
-		 */
-		intel_set_cpu_fifo_underrun_reporting(dev_priv, !pipe, false);
-		intel_set_pch_fifo_underrun_reporting(dev_priv, !pipe, false);
-	}
-
 	/* Only ilk+ has port A */
 	if (port == PORT_A)
 		ironlake_edp_pll_on(intel_dp);