Re: [PATCH v6 5/5] media: uvcvideo: Flush the control cache when we get an event

Laurent Pinchart
2024-12-19T00:31:36Z

Hi Ricardo,

Thank you for the patch.

On Tue, Dec 03, 2024 at 09:20:12PM +0000, Ricardo Ribalda wrote:
> Asynchronous controls trigger an event when they have completed their
> operation.
>
> This can make that the control cached value does not match the value in
> the device.
>
> Let's flush the cache to be on the safe side.
>
> Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>
> ---
> drivers/media/usb/uvc/uvc_ctrl.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/drivers/media/usb/uvc/uvc_ctrl.c b/drivers/media/usb/uvc/uvc_ctrl.c
> index 3dc9b7a49f64..db29e0e8bfd4 100644
> --- a/drivers/media/usb/uvc/uvc_ctrl.c
> +++ b/drivers/media/usb/uvc/uvc_ctrl.c
> @@ -1622,6 +1622,9 @@ void uvc_ctrl_status_event(struct uvc_video_chain *chain,
>
> mutex_lock(&chain->ctrl_mutex);
>
> + /* Flush the control cache, the data might have changed. */
> + ctrl->loaded = 0;
> +

That's better, covered by ctrl_mutex. There are however quite a few code
paths through which ctrl->loaded is accessed without holding the mutex
:-( Not a candidate for this series, but this should eventually be
fixed.

Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

> handle = ctrl->handle;
> if (handle)
> uvc_ctrl_set_handle(handle, ctrl, NULL);
>

--
Regards,

Laurent Pinchart