ozone: choose a card useful for display rather than by default

ui/ozone/platform/dri/dri_util.cc

 // Copyright 2014 The Chromium 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 "base/strings/stringprintf.h"
 #include "ui/ozone/platform/dri/dri_util.h"
 
 #include <errno.h>
+#include <fcntl.h>
 #include <stdint.h>
 #include <stdlib.h>
 #include <sys/mman.h>
 #include <xf86drm.h>
 #include <xf86drmMode.h>
 
 #include "ui/ozone/platform/dri/dri_wrapper.h"
 #include "ui/ozone/platform/dri/screen_manager.h"
 
 namespace ui {
 
 namespace {
 
+const char kDefaultGraphicsCardPattern[] = "/dev/dri/card%d";
+
 bool IsCrtcInUse(uint32_t crtc,
                  const ScopedVector<HardwareDisplayControllerInfo>& displays) {
   for (size_t i = 0; i < displays.size(); ++i) {
     if (crtc == displays[i]->crtc()->crtc_id)
       return true;
   }
 
   return false;
 }
 
@@ skipping 123 matching lines @@
   if (screen_manager->ConfigureDisplayController(
           drm, displays[0]->crtc()->crtc_id,
           displays[0]->connector()->connector_id, gfx::Point(),
           displays[0]->connector()->modes[0])) {
     if (dpms)
       drm->SetProperty(displays[0]->connector()->connector_id, dpms->prop_id,
                        DRM_MODE_DPMS_ON);
   }
 }
 
+base::FilePath GetFirstDisplayCardPath() {
+  struct drm_mode_card_res res;
+  for (int i = 0; /* end on first card# that does not exist */; i++) {
+    std::string card_path = base::StringPrintf(kDefaultGraphicsCardPattern, i);
+
+    if (access(card_path.c_str(), F_OK) != 0)
+      break;
+
+    int fd = open(card_path.c_str(), O_RDWR | O_CLOEXEC);
+    if (fd < 0)
+      continue;
+
+    memset(&res, 0, sizeof(struct drm_mode_card_res));
+    int ret = drmIoctl(fd, DRM_IOCTL_MODE_GETRESOURCES, &res);
+    close(fd);
+    if (ret == 0 && res.count_crtcs > 0) {
+      return base::FilePath(card_path);
+    }
+  }
+
+  return base::FilePath();
+}
+
 }  // namespace ui