render/egl, backend/wayland: add workaround for split render/display setups

Split render/display setups have two separate devices: one display-only
with a primary node, and one render-only with a render node. However
in these cases the EGL implementation and the Wayland compositor will
advertise the display device instead of the render device [1]. The EGL
implementation will magically open the render device when the display
device is passed in.

So just pass the display device as if it were a render device. Maybe in
the future Mesa will advertise the render device instead and we'll be
able to remove this workaround.

[1]: https://gitlab.freedesktop.org/mesa/mesa/-/issues/4178

backend/wayland/backend.c

@@ -143,7 +143,12 @@ static char *get_render_name(const char *name) {
 	if (match == NULL) {
 		wlr_log(WLR_ERROR, "Cannot find DRM device %s", name);
 	} else if (!(match->available_nodes & (1 << DRM_NODE_RENDER))) {
-		wlr_log(WLR_ERROR, "DRM device %s has no render node", name);
+		// Likely a split display/render setup. Pick the primary node and hope
+		// Mesa will open the right render node under-the-hood.
+		wlr_log(WLR_DEBUG, "DRM device %s has no render node, "
+			"falling back to primary node", name);
+		assert(match->available_nodes & (1 << DRM_NODE_PRIMARY));
+		render_name = strdup(match->nodes[DRM_NODE_PRIMARY]);
 	} else {
 		render_name = strdup(match->nodes[DRM_NODE_RENDER]);
 	}

render/egl.c

@@ -766,7 +766,12 @@ static char *get_render_name(const char *name) {
 	if (match == NULL) {
 		wlr_log(WLR_ERROR, "Cannot find DRM device %s", name);
 	} else if (!(match->available_nodes & (1 << DRM_NODE_RENDER))) {
-		wlr_log(WLR_ERROR, "DRM device %s has no render node", name);
+		// Likely a split display/render setup. Pick the primary node and hope
+		// Mesa will open the right render node under-the-hood.
+		wlr_log(WLR_DEBUG, "DRM device %s has no render node, "
+			"falling back to primary node", name);
+		assert(match->available_nodes & (1 << DRM_NODE_PRIMARY));
+		render_name = strdup(match->nodes[DRM_NODE_PRIMARY]);
 	} else {
 		render_name = strdup(match->nodes[DRM_NODE_RENDER]);
 	}