gbm: try to open a render node before the card device

Since render nodes allow rendering which should not interact with
the window system, we attempt to use render nodes first when a gbm
device is not directly specified.

The main difference as far as gbm is concerned is that render
nodes don't require drm master authentication.

Signed-off-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Chad Versace <chad.versace@linux.intel.com>

1 files changed, 18 insertions, 3 deletions

diff --git a/src/waffle/gbm/wgbm_display.c b/src/waffle/gbm/wgbm_display.c
index df94115..070ce70 100644
--- a/src/waffle/gbm/wgbm_display.c
+++ b/src/waffle/gbm/wgbm_display.c
@@ -65,7 +65,7 @@ wgbm_display_destroy(struct wcore_display *wc_self)
 }
 
 static int
-wgbm_get_fd(void)
+wgbm_get_default_fd_for_pattern(const char *pattern)
 {
     struct udev *ud;
     struct udev_enumerate *en;
@@ -77,7 +77,7 @@ wgbm_get_fd(void)
     ud = udev_new();
     en = udev_enumerate_new(ud);
     udev_enumerate_add_match_subsystem(en, "drm");
-    udev_enumerate_add_match_sysname(en, "card[0-9]*");
+    udev_enumerate_add_match_sysname(en, pattern);
     udev_enumerate_scan_devices(en);
 
     udev_list_entry_foreach(entry, udev_enumerate_get_list_entry(en)) {
@@ -94,6 +94,21 @@ wgbm_get_fd(void)
     return -1;
 }
 
+static int
+wgbm_get_default_fd(void)
+{
+    int fd;
+
+    // Try opening render node first
+    fd = wgbm_get_default_fd_for_pattern("renderD[0-9]*");
+    if (fd >= 0)
+        return fd;
+
+    // If render nodes are not supported, then fall back to the card
+    fd = wgbm_get_default_fd_for_pattern("card[0-9]*");
+    return fd;
+}
+
 struct wcore_display*
 wgbm_display_connect(struct wcore_platform *wc_plat,
                      const char *name)
@@ -109,7 +124,7 @@ wgbm_display_connect(struct wcore_platform *wc_plat,
     if (name != NULL) {
         fd = open(name, O_RDWR | O_CLOEXEC);
     } else {
-        fd = wgbm_get_fd();
+        fd = wgbm_get_default_fd();
     }
 
     if (fd < 0) {