i915: disable DAC on Ironlake also when doing CRT load detection.

Like on Sandybridge, disabling the DAC here when doing CRT load detect
avoids forever hangs waiting on the hardware.

test procedure on HP 2740p:
boot with no VGA plugged in, start X,
plug in VGA monitor (1280x1024)
chvt 3
machine hangs waiting forever.
Signed-off-by: Dave Airlie <airlied@redhat.com>
Signed-off-by: Eric Anholt <eric@anholt.net>

drivers/gpu/drm/i915/intel_crt.c

@@ -160,19 +160,20 @@ static bool intel_ironlake_crt_detect_hotplug(struct drm_connector *connector)
 	struct drm_i915_private *dev_priv = dev->dev_private;
 	u32 adpa, temp;
 	bool ret;
+	bool turn_off_dac = false;
 
 	temp = adpa = I915_READ(PCH_ADPA);
 
-	if (HAS_PCH_CPT(dev)) {
-		/* Disable DAC before force detect */
-		I915_WRITE(PCH_ADPA, adpa & ~ADPA_DAC_ENABLE);
-		(void)I915_READ(PCH_ADPA);
-	} else {
+	if (HAS_PCH_SPLIT(dev))
+		turn_off_dac = true;
+
 	adpa &= ~ADPA_CRT_HOTPLUG_MASK;
+	if (turn_off_dac)
+		adpa &= ~ADPA_DAC_ENABLE;
+
 	/* disable HPD first */
 	I915_WRITE(PCH_ADPA, adpa);
 	(void)I915_READ(PCH_ADPA);
-	}
 
 	adpa |= (ADPA_CRT_HOTPLUG_PERIOD_128 |
 			ADPA_CRT_HOTPLUG_WARMUP_10MS |
@@ -189,7 +190,7 @@ static bool intel_ironlake_crt_detect_hotplug(struct drm_connector *connector)
 		     1000, 1))
 		DRM_ERROR("timed out waiting for FORCE_TRIGGER");
 
-	if (HAS_PCH_CPT(dev)) {
+	if (turn_off_dac) {
 		I915_WRITE(PCH_ADPA, temp);
 		(void)I915_READ(PCH_ADPA);
 	}