lib/drmtest: Add comment explaining DRIVER_ANY excluding DRIVER_VGEM

Signed-off-by: Robert Foss <robert.foss@collabora.com>
Reviewed-by: Eric Engestrom <eric.engestrom@imgtec.com>

1 files changed, 7 insertions, 0 deletions

diff --git a/lib/drmtest.h b/lib/drmtest.h
index 19d4bd19..c9c019c0 100644
--- a/lib/drmtest.h
+++ b/lib/drmtest.h
@@ -42,8 +42,15 @@
 #define DRIVER_VC4	(1 << 1)
 #define DRIVER_VGEM	(1 << 2)
 #define DRIVER_VIRTIO	(1 << 3)
+/*
+ * Exclude DRVER_VGEM from DRIVER_ANY since if you run on a system
+ * with vgem as well as a supported driver, you can end up with a
+ * near-100% skip rate if you don't explicitly specify the device,
+ * depending on device-load ordering.
+ */
 #define DRIVER_ANY 	~(DRIVER_VGEM)
 
+
 #ifdef ANDROID
 #if (!(defined HAVE_MMAP64)) && (!(defined __x86_64__))
 extern void*  __mmap2(void *, size_t, int, int, int, off_t);