backend/drm: only keep track of local buffer

Stop keeping track of buffers on the parent GPU when multi-GPU is used.

This removes support for export_dmabuf on secondary GPUs, but renderer
v6 will bring this back by managing the swapchains in wlr_output instead
of the backends.

backend/drm/drm.c

@@ -630,10 +630,14 @@ static bool drm_connector_export_dmabuf(struct wlr_output *output,
 	struct wlr_drm_backend *drm = conn->backend;
 	struct wlr_drm_crtc *crtc = conn->crtc;
 
+	if (drm->parent) {
+		// We don't keep track of the original buffer on the parent GPU when
+		// using multi-GPU.
+		return false;
+	}
 	if (!drm->session->active) {
 		return false;
 	}
-
 	if (!crtc) {
 		return false;
 	}

backend/drm/renderer.c

@@ -304,7 +304,6 @@ void drm_fb_clear(struct wlr_drm_fb **fb_ptr) {
 	}
 
 	gbm_bo_destroy(fb->bo);
-	wlr_buffer_unlock(fb->local_wlr_buf);
 	wlr_buffer_unlock(fb->wlr_buf);
 	free(fb);
 
@@ -364,18 +363,16 @@ static struct gbm_bo *get_bo_for_dmabuf(struct gbm_device *gbm,
 }
 
 static struct wlr_drm_fb *drm_fb_create(struct wlr_drm_backend *drm,
-		struct wlr_buffer *buf, struct wlr_buffer *local_buf,
+		struct wlr_buffer *buf, const struct wlr_drm_format_set *formats) {
-		const struct wlr_drm_format_set *formats) {
 	struct wlr_drm_fb *fb = calloc(1, sizeof(*fb));
 	if (!fb) {
 		return NULL;
 	}
 
 	fb->wlr_buf = wlr_buffer_lock(buf);
-	fb->local_wlr_buf = wlr_buffer_lock(local_buf);
 
 	struct wlr_dmabuf_attributes attribs;
-	if (!wlr_buffer_get_dmabuf(local_buf, &attribs)) {
+	if (!wlr_buffer_get_dmabuf(buf, &attribs)) {
 		wlr_log(WLR_ERROR, "Failed to get DMA-BUF from buffer");
 		goto error_get_dmabuf;
 	}
@@ -411,7 +408,6 @@ static struct wlr_drm_fb *drm_fb_create(struct wlr_drm_backend *drm,
 error_get_fb_for_bo:
 	gbm_bo_destroy(fb->bo);
 error_get_dmabuf:
-	wlr_buffer_unlock(fb->local_wlr_buf);
 	wlr_buffer_unlock(fb->wlr_buf);
 	free(fb);
 	return NULL;
@@ -432,7 +428,7 @@ bool drm_fb_import(struct wlr_drm_fb **fb_ptr, struct wlr_drm_backend *drm,
 		local_buf = wlr_buffer_lock(buf);
 	}
 
-	struct wlr_drm_fb *fb = drm_fb_create(drm, buf, local_buf, formats);
+	struct wlr_drm_fb *fb = drm_fb_create(drm, local_buf, formats);
 	wlr_buffer_unlock(local_buf);
 	if (!fb) {
 		return false;

include/backend/drm/renderer.h

@@ -30,9 +30,7 @@ struct wlr_drm_surface {
 };
 
 struct wlr_drm_fb {
-	struct wlr_buffer *wlr_buf; // original buffer
+	struct wlr_buffer *wlr_buf;
-
-	struct wlr_buffer *local_wlr_buf; // GPU-local buffer
 	struct gbm_bo *bo;
 	uint32_t id;
 };