media: subdev: Don't report V4L2_SUBDEV_CAP_STREAMS when the streams API is disabled

Since the stream API is still experimental it is currently locked away
behind the internal, default disabled, v4l2_subdev_enable_streams_api flag.

Advertising V4L2_SUBDEV_CAP_STREAMS when the streams API is disabled
confuses userspace. E.g. it causes the following libcamera error:

ERROR SimplePipeline simple.cpp:1497 Failed to reset routes for
  /dev/v4l-subdev1: Inappropriate ioctl for device

Don't report V4L2_SUBDEV_CAP_STREAMS when the streams API is disabled
to avoid problems like this.
Reported-by: Dennis Bonke <admin@dennisbonke.com>
Fixes: 9a6b5bf4 ("media: add V4L2_SUBDEV_CAP_STREAMS")
Cc: stable@vger.kernel.org # for >= 6.3
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>

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

@@ -502,6 +502,13 @@ static long subdev_do_ioctl(struct file *file, unsigned int cmd, void *arg,
 				       V4L2_SUBDEV_CLIENT_CAP_STREAMS;
 	int rval;
 
+	/*
+	 * If the streams API is not enabled, remove V4L2_SUBDEV_CAP_STREAMS.
+	 * Remove this when the API is no longer experimental.
+	 */
+	if (!v4l2_subdev_enable_streams_api)
+		streams_subdev = false;
+
 	switch (cmd) {
 	case VIDIOC_SUBDEV_QUERYCAP: {
 		struct v4l2_subdev_capability *cap = arg;