Re: [PATCH] media: uvcvideo: preserve status URB interval on resubmit

Hi Xu

Good catch :)

On Thu, 13 Aug 2026 at 09:48, raoxu <[email protected]> wrote:
>
> From: Xu Rao <[email protected]>
>
> usb_fill_int_urb() takes an endpoint interval value and stores the
> period expected by usb_submit_urb() in urb->interval. For high-speed
> and SuperSpeed interrupt endpoints, it converts the logarithmic
> descriptor encoding to the corresponding microframe period.
>
> The UVC status URB is initialized once in uvc_status_init(), including
> the UVC_QUIRK_STATUS_INTERVAL adjustment required by high-speed devices
> that report bInterval using the old full-speed convention. The first
> submission therefore carries the intended interval.
>
> Both status resubmit paths, however, overwrite urb->interval with the
> raw endpoint bInterval before submitting the same URB again. On
> high-speed and SuperSpeed devices this mixes the descriptor encoding
> with the already converted URB interval representation. For devices
> using UVC_QUIRK_STATUS_INTERVAL it also deterministically discards the
> quirk adjustment after the first status completion, making the
> workaround effective only for the initial submission.
>
> This has been easy to miss because the initial status submission is
> correct, full-speed interrupt endpoints do not have the same
> logarithmic encoding mismatch, and the status endpoint carries
> relatively infrequent control and streaming notifications rather than
> the video payload itself. The problem only appears after the status URB
> has completed and is resubmitted, and the externally visible effect
> also depends on how the host controller handles the resulting period.
>
> Do not restore bInterval when resubmitting the status URB. Reuse the
> interval established by usb_fill_int_urb() and usb_submit_urb(), which
> also preserves the quirk-adjusted value. No additional state or
> interval conversion is needed because the same URB is being reused.
>
> Fixes: c0efd232929c ("V4L/DVB (8145a): USB Video Class driver")
> Fixes: e5225c820c05 ("media: uvcvideo: Send a control event when a Control Change interrupt arrives")
> Cc: [email protected]
Reviewed-by: Ricardo Ribalda <[email protected]>
> Signed-off-by: Xu Rao <[email protected]>
> ---
>  drivers/media/usb/uvc/uvc_ctrl.c   | 1 -
>  drivers/media/usb/uvc/uvc_status.c | 1 -
>  2 files changed, 2 deletions(-)
>
> diff --git a/drivers/media/usb/uvc/uvc_ctrl.c b/drivers/media/usb/uvc/uvc_ctrl.c
> index 3ca108b83f1d..6552f541aa0d 100644
> --- a/drivers/media/usb/uvc/uvc_ctrl.c
> +++ b/drivers/media/usb/uvc/uvc_ctrl.c
> @@ -2196,7 +2196,6 @@ static void uvc_ctrl_status_event_work(struct work_struct *work)
>                 return;
>
>         /* Resubmit the URB. */
> -       w->urb->interval = dev->int_ep->desc.bInterval;
>         ret = usb_submit_urb(w->urb, GFP_KERNEL);
>         if (ret < 0)
>                 dev_err(&dev->intf->dev,
> diff --git a/drivers/media/usb/uvc/uvc_status.c b/drivers/media/usb/uvc/uvc_status.c
> index b632cf5e3fe9..680c6c7f4ad7 100644
> --- a/drivers/media/usb/uvc/uvc_status.c
> +++ b/drivers/media/usb/uvc/uvc_status.c
> @@ -245,7 +245,6 @@ static void uvc_status_complete(struct urb *urb)
>         }
>
>         /* Resubmit the URB. */
> -       urb->interval = dev->int_ep->desc.bInterval;
>         ret = usb_submit_urb(urb, GFP_ATOMIC);
>         if (ret < 0)
>                 dev_err(&dev->intf->dev,
> --
> 2.50.1
>
>


-- 
Ricardo Ribalda