drm/i915: Add 30ms delay to make SDVO TV detection reliable.

Without this, on some boots the TV wouldn't be detected.  Testing
showed 15ms to be insufficient.

https://bugs.freedesktop.org/show_bug.cgi?id=24290
https://bugs.freedesktop.org/show_bug.cgi?id=20785

Signed-off-by: Zhao Yakui <yakui.zhao@intel.com>
Tested-by: Yan Seiner <yan@seiner.com>
Signed-off-by: Eric Anholt <eric@anholt.net>

drivers/gpu/drm/i915/intel_sdvo.c

@@ -1617,6 +1617,10 @@ static enum drm_connector_status intel_sdvo_detect(struct drm_connector *connect
 
 	intel_sdvo_write_cmd(intel_output,
 			     SDVO_CMD_GET_ATTACHED_DISPLAYS, NULL, 0);
+	if (sdvo_priv->is_tv) {
+		/* add 30ms delay when the output type is SDVO-TV */
+		mdelay(30);
+	}
 	status = intel_sdvo_read_response(intel_output, &response, 2);
 
 	DRM_DEBUG_KMS("SDVO response %d %d\n", response & 0xff, response >> 8);