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

This reverts commit bbdf0b2f ("drm/i915/bxt: Disable device ready
before shutdown command").

Disable device ready before shutdown command was added previously to
avoid a split screen issue seen on dual link DSI panels. As of now, dual
link is not supported and will need some rework in the upstream
code. For single link DSI panels, the change is not required. This will
cause failure in sending SHUTDOWN packet during disable. Hence reverting
the change. Will handle the change as part of dual link enabling in
upstream.

Fixes: bbdf0b2f ("drm/i915/bxt: Disable device ready before shutdown command")
Cc: <stable@vger.kernel.org> # v4.12+
Signed-off-by: Uma Shankar <uma.shankar@intel.com>
Signed-off-by: Vidya Srinivas <vidya.srinivas@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1504604671-17237-1-git-send-email-vidya.srinivas@intel.com

drivers/gpu/drm/i915/intel_dsi.c

@@ -892,8 +892,6 @@ static void intel_dsi_disable(struct intel_encoder *encoder,
 			      const struct intel_crtc_state *old_crtc_state,
 			      const 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;
 
@@ -902,15 +900,6 @@ static void intel_dsi_disable(struct intel_encoder *encoder,
 	intel_dsi_vbt_exec_sequence(intel_dsi, MIPI_SEQ_BACKLIGHT_OFF);
 	intel_panel_disable_backlight(old_conn_state);
 
-	/*
-	 * 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);
-	}
-
 	/*
 	 * According to the spec we should send SHUTDOWN before
 	 * MIPI_SEQ_DISPLAY_OFF only for v3+ VBTs, but field testing