drm/i915: Disable CPU underruns around eDP port and vdd enable on ILK-IVB

We sometimes get a spurious CPU pipe underrun somewhere between
enabling port A and enabling vdd for the panel. Observed on both
ILK and IVB with port A eDP. Suppress FIFO underrun reporting
around the port and vdd enable to avoid the dmesg errors.

Not sure if port D eDP would suffer from the same issue, but assume
that it doesn't until proven differently.

Testcase: igt/kms_setmode
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1448050160-14124-2-git-send-email-ville.syrjala@linux.intel.comAcked-by: Chris Wilson <chris@chris-wilson.co.uk>

drivers/gpu/drm/i915/intel_dp.c

@@ -2697,6 +2697,15 @@ static void intel_enable_dp(struct intel_encoder *encoder)
 	if (IS_VALLEYVIEW(dev))
 		vlv_init_panel_power_sequencer(intel_dp);
 
+	/*
+	 * We get an occasional spurious underrun between the port
+	 * enable and vdd enable, when enabling port A eDP.
+	 *
+	 * FIXME: Not sure if this applies to (PCH) port D eDP as well
+	 */
+	if (port == PORT_A)
+		intel_set_cpu_fifo_underrun_reporting(dev_priv, pipe, false);
+
 	intel_dp_enable_port(intel_dp);
 
 	if (port == PORT_A && IS_GEN5(dev_priv)) {
@@ -2714,6 +2723,9 @@ static void intel_enable_dp(struct intel_encoder *encoder)
 	edp_panel_on(intel_dp);
 	edp_panel_vdd_off(intel_dp, true);
 
+	if (port == PORT_A)
+		intel_set_cpu_fifo_underrun_reporting(dev_priv, pipe, true);
+
 	pps_unlock(intel_dp);
 
 	if (IS_VALLEYVIEW(dev)) {