libcamera: v4l2_subdevice: Enable streams API when supported

The streams API needs to be enabled explictly by setting a subdev client
capability. Do so unconditionally for subdevs that expose streams
support. We don't need any kernel version check to use the
VIDIOC_SUBDEV_S_CLIENT_CAP ioctl, as it is guaranteed to be supported by
kernels that support streams.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>
Tested-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

src/libcamera/v4l2_subdevice.cpp

@@ -359,6 +359,21 @@ int V4L2Subdevice::open()
 		return ret;
 	}
 
+	/* If the subdev supports streams, enable the streams API. */
+	if (caps_.hasStreams()) {
+		struct v4l2_subdev_client_capability clientCaps{};
+		clientCaps.capabilities = V4L2_SUBDEV_CLIENT_CAP_STREAMS;
+
+		ret = ioctl(VIDIOC_SUBDEV_S_CLIENT_CAP, &clientCaps);
+		if (ret < 0) {
+			ret = -errno;
+			LOG(V4L2, Error)
+				<< "Unable to set client capabilities: "
+				<< strerror(-ret);
+			return ret;
+		}
+	}
+
 	return 0;
 }