egl: Improve driver selection.

The idea is to be able to match a driver using the following order

  try egl_gallium with hw renderer
  try egl_dri2
  try egl_gallium with sw renderer
  try egl_glx

given the module list

  egl_gallium
  egl_dri2
  egl_glx

For that, UseFallback initialization option is added.  The module list
is matched twice: with the option unset and with the option set.  In the
first pass, egl_gallium skips its sw renderer and egl_glx rejects to
initialize since UseFallback is not set.  In the second pass,
egl_gallium skips its hw renderer and egl_dri2 rejects to initialize
since UseFallback is set.  The process stops at the first driver that
initializes the display.

1 files changed, 4 insertions, 0 deletions

diff --git a/src/egl/drivers/dri2/egl_dri2.c b/src/egl/drivers/dri2/egl_dri2.c
index 2e827f4f3e5..6fc1e49e773 100644
--- a/src/egl/drivers/dri2/egl_dri2.c
+++ b/src/egl/drivers/dri2/egl_dri2.c
@@ -1470,6 +1470,10 @@ dri2_initialize_drm(_EGLDriver *drv, _EGLDisplay *disp)
 static EGLBoolean
 dri2_initialize(_EGLDriver *drv, _EGLDisplay *disp)
 {
+   /* not until swrast_dri is supported */
+   if (disp->Options.UseFallback)
+      return EGL_FALSE;
+
    switch (disp->Platform) {
    case _EGL_PLATFORM_X11:
       if (disp->Options.TestOnly)