backend/drm: add wlr_drm_backend_get_parent()

Allows compositors to figure out whether a DRM backend is
secondary on a multi-GPU setup.

2 files changed, 10 insertions, 0 deletions

diff --git a/backend/drm/backend.c b/backend/drm/backend.c
index 4697234d..c50e278b 100644
--- a/backend/drm/backend.c
+++ b/backend/drm/backend.c
@@ -96,6 +96,11 @@ bool wlr_backend_is_drm(struct wlr_backend *b) {
 	return b->impl == &backend_impl;
 }
 
+struct wlr_backend *wlr_drm_backend_get_parent(struct wlr_backend *backend) {
+	struct wlr_drm_backend *drm = get_drm_backend_from_backend(backend);
+	return drm->parent ? &drm->parent->backend : NULL;
+}
+
 static void handle_session_active(struct wl_listener *listener, void *data) {
 	struct wlr_drm_backend *drm =
 		wl_container_of(listener, drm, session_active);
diff --git a/include/wlr/backend/drm.h b/include/wlr/backend/drm.h
index e4fdf65d..e8f9f6a3 100644
--- a/include/wlr/backend/drm.h
+++ b/include/wlr/backend/drm.h
@@ -44,6 +44,11 @@ bool wlr_backend_is_drm(struct wlr_backend *backend);
 bool wlr_output_is_drm(struct wlr_output *output);
 
 /**
+ * Get the parent DRM backend, if any.
+ */
+struct wlr_backend *wlr_drm_backend_get_parent(struct wlr_backend *backend);
+
+/**
  * Get the KMS connector object ID.
  */
 uint32_t wlr_drm_connector_get_id(struct wlr_output *output);