media: v4l: subdev: Return routes set using S_ROUTING

Return the routes set using S_ROUTING back to the user. Also reflect this
in documentation.

Signed-off-by: Sakari Ailus <[e-mail]>
Reviewed-by: Laurent Pinchart <[e-mail]>
Signed-off-by: Hans Verkuil <[e-mail]>

Documentation/userspace-api/media/v4l/vidioc-subdev-g-routing.rst

···
 ``VIDIOC_SUBDEV_G_ROUTING`` ioctl and application may enable or disable routes
 with the ``VIDIOC_SUBDEV_S_ROUTING`` ioctl, by adding or removing routes and
 setting or clearing flags of the ``flags`` field of a struct
-:c:type:`v4l2_subdev_route`.
+:c:type:`v4l2_subdev_route`. Similarly to ``VIDIOC_SUBDEV_G_ROUTING``, also
+``VIDIOC_SUBDEV_S_ROUTING`` returns the routes back to the user.
 
 All stream configurations are reset when ``VIDIOC_SUBDEV_S_ROUTING`` is called.
 This means that the userspace must reconfigure all stream formats and selections
···
 On success 0 is returned, on error -1 and the ``errno`` variable is set
 appropriately. The generic error codes are described at the
 :ref:`Generic Error Codes <gen-errors>` chapter.
-
-ENOSPC
-   The application provided ``num_routes`` is not big enough to contain
-   all the available routes the subdevice exposes.
 
 EINVAL
    The sink or source pad identifiers reference a non-existing pad or reference

drivers/media/v4l2-core/v4l2-subdev.c

···
 		krouting.len_routes = routing->len_routes;
 		krouting.routes = routes;
 
-		return v4l2_subdev_call(sd, pad, set_routing, state,
+		rval = v4l2_subdev_call(sd, pad, set_routing, state,
 					routing->which, &krouting);
+		if (rval < 0)
+			return rval;
+
+		memcpy((struct v4l2_subdev_route *)(uintptr_t)routing->routes,
+		       state->routing.routes,
+		       min(state->routing.num_routes, routing->len_routes) *
+		       sizeof(*state->routing.routes));
+		routing->num_routes = state->routing.num_routes;
+
+		return 0;
 	}
 
 	case VIDIOC_SUBDEV_G_CLIENT_CAP: {