On Mon, Jun 30, 2025 at 02:20:30PM +0000, Ricardo Ribalda wrote:
> If we subscribe to an event with V4L2_EVENT_SUB_FL_SEND_INITIAL, the
> driver needs to report back some values that require the camera to be
> powered on. But VIDIOC_SUBSCRIBE_EVENT is not part of the ioctls that
> turn on the camera.
>
> We could unconditionally turn on the camera during
> VIDIOC_SUBSCRIBE_EVENT, but it is more efficient to turn it on only
> during V4L2_EVENT_SUB_FL_SEND_INITIAL, which we believe is not a common
> usecase.
>
> To avoid a list_del if uvc_pm_get() fails, we move list_add_tail to the
> end of the function.
>
> Reviewed-by: Hans de Goede <hansg@kernel.org>
> Fixes: d1b618e79548 ("media: uvcvideo: Do not turn on the camera for some ioctls")
> Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>
> ---
> drivers/media/usb/uvc/uvc_ctrl.c | 8 +++++++-
> 1 file changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/media/usb/uvc/uvc_ctrl.c b/drivers/media/usb/uvc/uvc_ctrl.c
> index 303b7509ec47964dc1bf0e28127075b4a3867511..e84aaf130c73403a6c818deceadf404a2975c816 100644
> --- a/drivers/media/usb/uvc/uvc_ctrl.c
> +++ b/drivers/media/usb/uvc/uvc_ctrl.c
> @@ -2072,18 +2072,23 @@ static int uvc_ctrl_add_event(struct v4l2_subscribed_event *sev, unsigned elems)
> goto done;
> }
>
> - list_add_tail(&sev->node, &mapping->ev_subs);
> if (sev->flags & V4L2_EVENT_SUB_FL_SEND_INITIAL) {
> struct v4l2_event ev;
> u32 changes = V4L2_EVENT_CTRL_CH_FLAGS;
> s32 val = 0;
>
> + ret = uvc_pm_get(handle->chain->dev);
> + if (ret)
> + goto done;
> +
> if (uvc_ctrl_mapping_is_compound(mapping) ||
> __uvc_ctrl_get(handle->chain, ctrl, mapping, &val) == 0)
> changes |= V4L2_EVENT_CTRL_CH_VALUE;
>
> uvc_ctrl_fill_event(handle->chain, &ev, ctrl, mapping, val,
> changes);
> +
> + uvc_pm_put(handle->chain->dev);
Add a blank line here.
> /*
> * Mark the queue as active, allowing this initial event to be
> * accepted.
> @@ -2092,6 +2097,7 @@ static int uvc_ctrl_add_event(struct v4l2_subscribed_event *sev, unsigned elems)
> v4l2_event_queue_fh(sev->fh, &ev);
> }
>
> + list_add_tail(&sev->node, &mapping->ev_subs);
And here.
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> done:
> mutex_unlock(&handle->chain->ctrl_mutex);
> return ret;
>
--
Regards,
Laurent Pinchart