drm/i915/tv: Sleep before checking for state changes.

We need to wait for the PLLs to settle prior to detecting the state
changes. The BIOS writers guide suggests waiting for the next vblank.
Reported-by: NCarlos R. Mafra <crmafra2@gmail.com>
Signed-off-by: NChris Wilson <chris@chris-wilson.co.uk>

drivers/gpu/drm/i915/intel_tv.c

@@ -1271,8 +1271,12 @@ intel_tv_detect_type (struct intel_tv *intel_tv)
 	I915_WRITE(TV_DAC, tv_dac);
 	POSTING_READ(TV_DAC);
 
+	intel_wait_for_vblank(intel_tv->base.base.dev,
+			      to_intel_crtc(intel_tv->base.base.crtc)->pipe);
+
 	type = -1;
 	if (wait_for((tv_dac = I915_READ(TV_DAC)) & TVDAC_STATE_CHG, 20) == 0) {
+		DRM_DEBUG_KMS("TV detected: %x, %x\n", tv_ctl, tv_dac);
 		/*
 		 *  A B C
 		 *  0 1 1 Composite
@@ -1289,8 +1293,7 @@ intel_tv_detect_type (struct intel_tv *intel_tv)
 			DRM_DEBUG_KMS("Detected Component TV connection\n");
 			type = DRM_MODE_CONNECTOR_Component;
 		} else {
-			DRM_DEBUG_KMS("Unrecognised TV connection: %x\n",
-				      tv_dac);
+			DRM_DEBUG_KMS("Unrecognised TV connection\n");
 		}
 	}