Avoid a kernel driver / X server crash situation.

monitor_reconfigure_main.cc

 // Copyright (c) 2010 The Chromium OS Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "monitor_reconfig/monitor_reconfigure_main.h"
 
 #include <algorithm>
 #include <cstdio>
 #include <cstdlib>
 
@@ skipping 38 matching lines @@
   string lcd_resolution, external_resolution, screen_resolution;
   CHECK(selector.FindBestResolutions(lcd_modes,
                                      external_modes,
                                      &lcd_resolution,
                                      &external_resolution,
                                      &screen_resolution));
   CHECK(!lcd_resolution.empty() || !external_resolution.empty());
 
   // Disable the LCD if we were told to do so (because we're using a higher
   // resolution that'd be clipped on the LCD).
-  if (!lcd_resolution.empty())
-    SetDeviceResolution(lcd_output_->name, lcd_resolution);
-  else
+  if (lcd_resolution.empty())
     DisableDevice(lcd_output_->name);
 
   // If there's no external output connected, disable the device before we try
   // to set the screen resolution; otherwise xrandr will complain if we're
   // trying to set the screen to a smaller size than what the now-unplugged
   // device was using.
+  if (external_resolution.empty())
+    DisableDevice(external_output_->name);
+
+  // Set the fb to try to avoid the driver's "crtc has no fb" message.
+  // Doing this before enabling the display reduces the likelihood of a
+  // visible "snap" when returning to the panel.
+  SetScreenResolution(screen_resolution);
+
+  // Enable the LCD if appropriate.
+  if (!lcd_resolution.empty())
+    SetDeviceResolution(lcd_output_->name, lcd_resolution);
+
+  // Enable the external device if appropriate.
   if (!external_resolution.empty())
     SetDeviceResolution(external_output_->name, external_resolution);
-  else
-    DisableDevice(external_output_->name);
-
-  SetScreenResolution(screen_resolution);
 }
 
 void MonitorReconfigureMain::DetermineOutputs() {
   CHECK(screen_info_->noutput > 1) << "Expected at least two outputs";
   XRROutputInfo* first_output =
       XRRGetOutputInfo(display_, screen_info_, screen_info_->outputs[0]);
   XRROutputInfo* second_output =
       XRRGetOutputInfo(display_, screen_info_, screen_info_->outputs[1]);
 
   if (strcmp(first_output->name, kLcdOutputName) == 0) {
@@ skipping 69 matching lines @@
                        logging::APPEND_TO_OLD_LOG_FILE);
   Display* display = XOpenDisplay(NULL);
   CHECK(display) << "Could not open display";
 
   Window window = RootWindow(display, DefaultScreen(display));
   XRRScreenResources* screen_info = XRRGetScreenResources(display, window);
   monitor_reconfig::MonitorReconfigureMain main_app(display, screen_info);
   main_app.Run();
   return 0;
 }