drm/i915/bxt: Disable device ready before shutdown command

Disable device ready before MIPI port shutdown command.
This helps to avoid mipi split screen issues.
Signed-off-by: Uma Shankar <uma.shankar@intel.com>
Signed-off-by: Vidya Srinivas <vidya.srinivas@intel.com>
Reviewed-by: Bob Paauwe <bob.j.paauwe@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1486551058-22596-8-git-send-email-vidya.srinivas@intel.com

drivers/gpu/drm/i915/intel_dsi.c

@@ -612,6 +612,8 @@ static void intel_dsi_pre_disable(struct intel_encoder *encoder,
 				  struct intel_crtc_state *old_crtc_state,
 				  struct drm_connector_state *old_conn_state)
 {
+	struct drm_device *dev = encoder->base.dev;
+	struct drm_i915_private *dev_priv = dev->dev_private;
 	struct intel_dsi *intel_dsi = enc_to_intel_dsi(&encoder->base);
 	enum port port;
 
@@ -619,6 +621,15 @@ static void intel_dsi_pre_disable(struct intel_encoder *encoder,
 
 	intel_panel_disable_backlight(intel_dsi->attached_connector);
 
+	/*
+	 * Disable Device ready before the port shutdown in order
+	 * to avoid split screen
+	 */
+	if (IS_BROXTON(dev_priv)) {
+		for_each_dsi_port(port, intel_dsi->ports)
+			I915_WRITE(MIPI_DEVICE_READY(port), 0);
+	}
+
 	if (is_vid_mode(intel_dsi)) {
 		/* Send Shutdown command to the panel in LP mode */
 		for_each_dsi_port(port, intel_dsi->ports)