egl/glx: add fallback for zink loading

if the driver attemping to load is not zink and not software, then
attempt a zink fallback on failure

this conservatively handles the case of "only zink is built", though it
is going to be noticeably slower at startup than loading zink directly

Reviewed-by: Adam Jackson <ajax@redhat.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/16168>

src/egl/main/eglapi.c

@@ -662,12 +662,26 @@ eglInitialize(EGLDisplay dpy, EGLint *major, EGLint *minor)
        * If the initialisation fails, try again using only software rendering.
        */
       if (!_eglDriver.Initialize(disp)) {
-         if (disp->Options.ForceSoftware)
+         bool fail = true;
-            RETURN_EGL_ERROR(disp, EGL_NOT_INITIALIZED, EGL_FALSE);
+         if (!disp->Options.ForceSoftware && !disp->Options.Zink &&
-         else {
+             !env_var_as_boolean("LIBGL_KOPPER_DISABLE", false) && !getenv("GALLIUM_DRIVER")) {
+            /* zink fallback */
+            disp->Options.Zink = EGL_TRUE;
             disp->Options.ForceSoftware = EGL_TRUE;
-            if (!_eglDriver.Initialize(disp))
+            fail = !_eglDriver.Initialize(disp);
+            if (fail) {
+               disp->Options.Zink = EGL_FALSE;
+               disp->Options.ForceSoftware = EGL_FALSE;
+            }
+         }
+         if (fail) {
+            if (disp->Options.ForceSoftware)
                RETURN_EGL_ERROR(disp, EGL_NOT_INITIALIZED, EGL_FALSE);
+            else {
+               disp->Options.ForceSoftware = EGL_TRUE;
+               if (!_eglDriver.Initialize(disp))
+                  RETURN_EGL_ERROR(disp, EGL_NOT_INITIALIZED, EGL_FALSE);
+            }
          }
       }
 

src/glx/drisw_glx.c

@@ -1055,11 +1055,8 @@ static struct glx_screen *
 driswCreateScreen(int screen, struct glx_display *priv)
 {
    const struct drisw_display *pdpyp = (struct drisw_display *)priv->driswDisplay;
-   if (pdpyp->zink && !env_var_as_boolean("LIBGL_KOPPER_DISABLE", false)) {
-      return driswCreateScreenDriver(screen, priv, "zink");
-   }
 
-    return driswCreateScreenDriver(screen, priv, "swrast");
+   return driswCreateScreenDriver(screen, priv, pdpyp->zink ? "zink" : "swrast");
 }
 
 /* Called from __glXFreeDisplayPrivate.

src/glx/glxext.c

@@ -926,9 +926,9 @@ __glXInitialize(Display * dpy)
 #if defined(GLX_DIRECT_RENDERING) && !defined(GLX_USE_APPLEGL)
    glx_direct = !env_var_as_boolean("LIBGL_ALWAYS_INDIRECT", false);
    glx_accel = !env_var_as_boolean("LIBGL_ALWAYS_SOFTWARE", false);
-   Bool zink;
    const char *env = getenv("MESA_LOADER_DRIVER_OVERRIDE");
-   zink = env && !strcmp(env, "zink");
+   Bool explicit_zink = env && !strcmp(env, "zink");
+   Bool infer_zink = false;
 
    dpyPriv->drawHash = __glxHashCreate();
 
@@ -945,17 +945,20 @@ __glXInitialize(Display * dpy)
     ** (e.g., those called in AllocAndFetchScreenConfigs).
     */
 #if defined(GLX_USE_DRM)
-   if (glx_direct && glx_accel && !zink) {
+   if (glx_direct && glx_accel && !explicit_zink) {
 #if defined(HAVE_DRI3)
       if (!env_var_as_boolean("LIBGL_DRI3_DISABLE", false))
          dpyPriv->dri3Display = dri3_create_display(dpy);
 #endif /* HAVE_DRI3 */
       if (!env_var_as_boolean("LIBGL_DRI2_DISABLE", false))
          dpyPriv->dri2Display = dri2CreateDisplay(dpy);
+      /* zink fallback */
+      if (!dpyPriv->dri3Display && !dpyPriv->dri2Display)
+         infer_zink =  !env_var_as_boolean("LIBGL_KOPPER_DISABLE", false) && !getenv("GALLIUM_DRIVER");
    }
 #endif /* GLX_USE_DRM */
    if (glx_direct)
-      dpyPriv->driswDisplay = driswCreateDisplay(dpy, zink);
+      dpyPriv->driswDisplay = driswCreateDisplay(dpy, explicit_zink | infer_zink);
 #endif /* GLX_DIRECT_RENDERING && !GLX_USE_APPLEGL */
 
 #ifdef GLX_USE_APPLEGL
@@ -971,8 +974,17 @@ __glXInitialize(Display * dpy)
 #endif
 
    if (!AllocAndFetchScreenConfigs(dpy, dpyPriv)) {
-      free(dpyPriv);
+      Bool fail = true;
-      return NULL;
+      /* if zink was inferred, retry without zink */
+      if (infer_zink && !explicit_zink) {
+         free(dpyPriv->screens);
+         driswCreateDisplay(dpy, false);
+         fail = !AllocAndFetchScreenConfigs(dpy, dpyPriv);
+      }
+      if (fail) {
+         free(dpyPriv);
+         return NULL;
+      }
    }
 
    __glX_send_client_info(dpyPriv);