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>
 
 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 100 matching lines @@
                  fd,
                  map_request.offset);
   if (*pixels == MAP_FAILED) {
     VLOG(2) << "Cannot mmap dumb buffer (" << errno << ") " << strerror(errno);
     return false;
   }
 
   return true;
 }
 
+int OpenFirstDisplayCard() {
+  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);

[marcheu, 2015/02/13 04:34:42]

I'm going to nitpick. In some cases, we can have a driver which answers
positively to the getresources ioctl, but which has no resources to use. So, you
probably want to add a check that the number of CRTCs is >0.

[Zach Reizner, 2015/02/13 18:45:15]

I agree.

+    if (ret == 0) {
+      return fd;
+    }
+
+    close(fd);
+  }
+
+  return -1;
+}
+
 }  // namespace ui