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.

2 files changed, 6 insertions, 0 deletions

diff --git a/src/egl/main/egldisplay.h b/src/egl/main/egldisplay.h
index b42760b..dbc5d32 100644
--- a/src/egl/main/egldisplay.h
+++ b/src/egl/main/egldisplay.h
@@ -93,6 +93,7 @@ struct _egl_display
    /* options that affect how the driver initializes the display */
    struct {
       EGLBoolean TestOnly;    /**< Driver should not set fields when true */
+      EGLBoolean UseFallback; /**< Use fallback driver (sw or less features) */
    } Options;
 
    /* these fields are set by the driver during init */
diff --git a/src/egl/main/egldriver.c b/src/egl/main/egldriver.c
index 7baa24f..e133c22 100644
--- a/src/egl/main/egldriver.c
+++ b/src/egl/main/egldriver.c
@@ -585,8 +585,13 @@ _eglMatchDriver(_EGLDisplay *dpy, EGLBoolean test_only)
 
    /* set options */
    dpy->Options.TestOnly = test_only;
+   dpy->Options.UseFallback = EGL_FALSE;
 
    best_drv = _eglMatchAndInitialize(dpy);
+   if (!best_drv) {
+      dpy->Options.UseFallback = EGL_TRUE;
+      best_drv = _eglMatchAndInitialize(dpy);
+   }
 
    _eglUnlockMutex(&_eglModuleMutex);