libweston: Add the ability to determine if a dmabuf is scanout-capable

Adds a new callback 'can_scanout_dmabuf' in weston_backend, which
can be set by the back-end do determine if the buffer supplied can be
imported directly by KMS.

This patch adds a wrapper over it, 'weston_compositor_dmabuf_can_scanout'
which is called before importing the dmabuf in the GPU if the
direct_display dmabuf is being set. If that's true and the check
failed, we refuse to create a wl_buffer.

This patch avoids importing in the GPU.

Signed-off-by: Marius Vlad <marius.vlad@collabora.com>

libweston/backend.h

@@ -95,6 +95,18 @@ struct weston_backend {
 	 */
 	void (*device_changed)(struct weston_compositor *compositor,
 			       dev_t device, bool added);
+
+	/** Verifies if the dmabuf can be used directly/scanned-out by the HW.
+	 *
+	 * @param compositor The compositor.
+	 * @param buffer The dmabuf to verify.
+	 *
+	 * Determines if the buffer can be imported directly by the display
+	 * controller/HW. Back-ends can use this to check if the supplied
+	 * buffer can be scanned-out, as to void importing it into the GPU.
+	 */
+	bool (*can_scanout_dmabuf)(struct weston_compositor *compositor,
+				   struct linux_dmabuf_buffer *buffer);
 };
 
 /* weston_head */

libweston/compositor.c

@@ -7519,6 +7519,18 @@ weston_compositor_import_dmabuf(struct weston_compositor *compositor,
 	return renderer->import_dmabuf(compositor, buffer);
 }
 
+WL_EXPORT bool
+weston_compositor_dmabuf_can_scanout(struct weston_compositor *compositor,
+		struct linux_dmabuf_buffer *buffer)
+{
+	struct weston_backend *backend = compositor->backend;
+
+	if (backend->can_scanout_dmabuf == NULL)
+		return false;
+
+	return backend->can_scanout_dmabuf(compositor, buffer);
+}
+
 WL_EXPORT void
 weston_version(int *major, int *minor, int *micro)
 {

libweston/libweston-internal.h

@@ -79,6 +79,9 @@ weston_compositor_add_pending_output(struct weston_output *output,
 bool
 weston_compositor_import_dmabuf(struct weston_compositor *compositor,
 				struct linux_dmabuf_buffer *buffer);
+bool
+weston_compositor_dmabuf_can_scanout(struct weston_compositor *compositor,
+					struct linux_dmabuf_buffer *buffer);
 void
 weston_compositor_offscreen(struct weston_compositor *compositor);
 

libweston/linux-dmabuf.c

@@ -259,9 +259,18 @@ params_create_common(struct wl_client *client,
 		}
 	}
 
+	if (buffer->direct_display) {
+		if (!weston_compositor_dmabuf_can_scanout(buffer->compositor,
+							  buffer))
+			goto err_failed;
+
+		goto avoid_gpu_import;
+	}
+
 	if (!weston_compositor_import_dmabuf(buffer->compositor, buffer))
 		goto err_failed;
 
+avoid_gpu_import:
 	buffer->buffer_resource = wl_resource_create(client,
 						     &wl_buffer_interface,
 						     1, buffer_id);
@@ -368,6 +377,7 @@ linux_dmabuf_create_params(struct wl_client *client,
 		wl_resource_create(client,
 				   &zwp_linux_buffer_params_v1_interface,
 				   version, params_id);
+	buffer->direct_display = false;
 	if (!buffer->params_resource)
 		goto err_dealloc;