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

ui/ozone/platform/dri/dri_util.cc

Index: ui/ozone/platform/dri/dri_util.cc
diff --git a/ui/ozone/platform/dri/dri_util.cc b/ui/ozone/platform/dri/dri_util.cc
index 5305f6d0b48f891031a158f9ea9814fca9ec5356..77230e561506e3c62b85d3971cdbd25c3b55204a 100644
--- a/ui/ozone/platform/dri/dri_util.cc
+++ b/ui/ozone/platform/dri/dri_util.cc
@@ -2,9 +2,11 @@
 // 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>
@@ -15,6 +17,8 @@ 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) {
@@ -135,4 +139,28 @@ bool MapDumbBuffer(int fd,
   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