drm/i915/icl: Disable DDI function

This patch disables DDI function by writing to
TRANS_DDI_FUNC_CTL registers of DSI ports as part
of DSI disable sequence.
Signed-off-by: Madhav Chauhan <madhav.chauhan@intel.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/b0088d643247135ba96943fa14625f5a43f43633.1540900289.git.jani.nikula@intel.com

drivers/gpu/drm/i915/icl_dsi.c

@@ -833,6 +833,14 @@ static void gen11_dsi_deconfigure_trancoder(struct intel_encoder *encoder)
 				10))
 			DRM_ERROR("DSI link not in ULPS\n");
 	}
+
+	/* disable ddi function */
+	for_each_dsi_port(port, intel_dsi->ports) {
+		dsi_trans = dsi_port_to_transcoder(port);
+		tmp = I915_READ(TRANS_DDI_FUNC_CTL(dsi_trans));
+		tmp &= ~TRANS_DDI_FUNC_ENABLE;
+		I915_WRITE(TRANS_DDI_FUNC_CTL(dsi_trans), tmp);
+	}
 }
 
 static void __attribute__((unused)) gen11_dsi_disable(