Re: [PATCH] usb: musb: musb_host: Introduce postponed URB giveback
From: Matwey V. Kornilov
Date: Sat Nov 04 2017 - 10:06:27 EST
Hi Bin,
I've just checked that the issue is still present in 4.13.10.
2017-04-27 13:20 GMT+03:00 Matwey V. Kornilov <matwey@xxxxxxxxxx>:
> This commit changes the order of actions undertaken in
> musb_advance_schedule() in order to overcome issue with broken
> isochronous transfer [1].
>
> There is no harm to split musb_giveback into two pieces. The first
> unlinks finished urb, the second givebacks it. The issue here that
> givebacking may be quite time-consuming due to urb->complete() call.
> As it happens in case of pwc-driven web cameras. It may take about 0.5
> ms to call __musb_giveback() that calls urb->callback() internally.
> Under specific circumstances setting MUSB_RXCSR_H_REQPKT in subsequent
> musb_start_urb() for the next urb will be too late to produce physical
> IN packet. Since auto req is not used by this module the exchange
> would be as the following:
>
> [ ] 7.220456 d= 0.000997 [182 + 3.667] [ 3] IN : 4.5
> [ T ] 7.220459 d= 0.000003 [182 + 7.000] [800] DATA0: [skipped]
> [ ] 7.222456 d= 0.001997 [184 + 3.667] [ 3] IN : 4.5
> [ ] 7.222459 d= 0.000003 [184 + 7.000] [ 3] DATA0: 00 00
>
> It is known that missed IN in isochronous mode makes some
> perepherial broken. For instance, pwc-driven or uvc-driven
> web cameras.
> In order to workaround this issue we postpone calling
> urb->callback() after setting MUSB_RXCSR_H_REQPKT for the
> next urb if there is the next urb pending in queue.
>
> [1] https://www.spinics.net/lists/linux-usb/msg145747.html
>
> Fixes: f551e1352983 ("Revert "usb: musb: musb_host: Enable HCD_BH flag to handle urb return in bottom half"")
> Signed-off-by: Matwey V. Kornilov <matwey@xxxxxxxxxx>
> ---
> drivers/usb/musb/musb_host.c | 54 +++++++++++++++++++++++++++++++++++++-------
> 1 file changed, 46 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/usb/musb/musb_host.c b/drivers/usb/musb/musb_host.c
> index ac3a4952abb4..b590c2555dab 100644
> --- a/drivers/usb/musb/musb_host.c
> +++ b/drivers/usb/musb/musb_host.c
> @@ -299,19 +299,24 @@ musb_start_urb(struct musb *musb, int is_in, struct musb_qh *qh)
> }
> }
>
> -/* Context: caller owns controller lock, IRQs are blocked */
> -static void musb_giveback(struct musb *musb, struct urb *urb, int status)
> +static void __musb_giveback(struct musb *musb, struct urb *urb, int status)
> __releases(musb->lock)
> __acquires(musb->lock)
> {
> - trace_musb_urb_gb(musb, urb);
> -
> - usb_hcd_unlink_urb_from_ep(musb->hcd, urb);
> spin_unlock(&musb->lock);
> usb_hcd_giveback_urb(musb->hcd, urb, status);
> spin_lock(&musb->lock);
> }
>
> +/* Context: caller owns controller lock, IRQs are blocked */
> +static void musb_giveback(struct musb *musb, struct urb *urb, int status)
> +{
> + trace_musb_urb_gb(musb, urb);
> +
> + usb_hcd_unlink_urb_from_ep(musb->hcd, urb);
> + __musb_giveback(musb, urb, status);
> +}
> +
> /* For bulk/interrupt endpoints only */
> static inline void musb_save_toggle(struct musb_qh *qh, int is_in,
> struct urb *urb)
> @@ -346,6 +351,7 @@ static void musb_advance_schedule(struct musb *musb, struct urb *urb,
> struct musb_hw_ep *ep = qh->hw_ep;
> int ready = qh->is_ready;
> int status;
> + int postponed_giveback = 0;
>
> status = (urb->status == -EINPROGRESS) ? 0 : urb->status;
>
> @@ -361,9 +367,35 @@ static void musb_advance_schedule(struct musb *musb, struct urb *urb,
> break;
> }
>
> - qh->is_ready = 0;
> - musb_giveback(musb, urb, status);
> - qh->is_ready = ready;
> + usb_hcd_unlink_urb_from_ep(musb->hcd, urb);
> +
> + /* It may take about 0.5 ms to call __musb_giveback() that
> + * calls urb->callback() internally. Under specific circumstances
> + * setting MUSB_RXCSR_H_REQPKT in subsequent musb_start_urb() for the
> + * next urb will be too late to produce physical IN packet. Since
> + * auto req is not used by this module the exchange would be as the
> + * following:
> + *
> + * [ ] 7.220456 d= 0.000997 [182 + 3.667] [ 3] IN : 4.5
> + * [ T ] 7.220459 d= 0.000003 [182 + 7.000] [800] DATA0: [skipped]
> + * [ ] 7.222456 d= 0.001997 [184 + 3.667] [ 3] IN : 4.5
> + * [ ] 7.222459 d= 0.000003 [184 + 7.000] [ 3] DATA0: 00 00
> + *
> + * It is known that missed IN in isochronous mode makes some
> + * perepherial broken. For instance, pwc-driven or uvc-driven
> + * web cameras.
> + * In order to workaround this issue we postpone calling
> + * urb->callback() after setting MUSB_RXCSR_H_REQPKT for the
> + * next urb if there is the next urb pending in queue.
> + */
> + if (is_in && qh->type == USB_ENDPOINT_XFER_ISOC
> + && !list_empty(&qh->hep->urb_list)) {
> + postponed_giveback = 1;
> + } else {
> + qh->is_ready = 0;
> + __musb_giveback(musb, urb, status);
> + qh->is_ready = ready;
> + }
>
> /* reclaim resources (and bandwidth) ASAP; deschedule it, and
> * invalidate qh as soon as list_empty(&hep->urb_list)
> @@ -428,6 +460,12 @@ static void musb_advance_schedule(struct musb *musb, struct urb *urb,
> hw_ep->epnum, is_in ? 'R' : 'T', next_urb(qh));
> musb_start_urb(musb, is_in, qh);
> }
> +
> + if (postponed_giveback) {
> + qh->is_ready = 0;
> + __musb_giveback(musb, urb, status);
> + qh->is_ready = ready;
> + }
> }
>
> static u16 musb_h_flush_rxfifo(struct musb_hw_ep *hw_ep, u16 csr)
> --
> 2.12.0
>
--
With best regards,
Matwey V. Kornilov.
Sternberg Astronomical Institute, Lomonosov Moscow State University, Russia
119234, Moscow, Universitetsky pr-k 13, +7 (495) 9392382