linux-kernel - Re: [PATCH v2] usb: dwc3: gadget: Check for IOC/LST bit in TRB->ctrl fields

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Date:   Tue, 28 Jan 2020 09:55:50 -0800
From:   John Stultz <john.stultz@...aro.org>
To:     Felipe Balbi <balbi@...nel.org>
Cc:     lkml <linux-kernel@...r.kernel.org>,
        Anurag Kumar Vulisha <anurag.kumar.vulisha@...inx.com>,
        Yang Fei <fei.yang@...el.com>,
        Thinh Nguyen <thinhn@...opsys.com>,
        Tejas Joglekar <tejas.joglekar@...opsys.com>,
        Andrzej Pietrasiewicz <andrzej.p@...labora.com>,
        Jack Pham <jackp@...eaurora.org>, Todd Kjos <tkjos@...gle.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        Linux USB List <linux-usb@...r.kernel.org>,
        stable <stable@...r.kernel.org>
Subject: Re: [PATCH v2] usb: dwc3: gadget: Check for IOC/LST bit in TRB->ctrl fields

On Tue, Jan 28, 2020 at 5:23 AM Felipe Balbi <balbi@...nel.org> wrote:
>
>
> Hi,
>
> John Stultz <john.stultz@...aro.org> writes:
>
> > From: Anurag Kumar Vulisha <anurag.kumar.vulisha@...inx.com>
> >
> > The current code in dwc3_gadget_ep_reclaim_completed_trb() will
> > check for IOC/LST bit in the event->status and returns if
> > IOC/LST bit is set. This logic doesn't work if multiple TRBs
> > are queued per request and the IOC/LST bit is set on the last
> > TRB of that request.
> >
> > Consider an example where a queued request has multiple queued
> > TRBs and IOC/LST bit is set only for the last TRB. In this case,
> > the core generates XferComplete/XferInProgress events only for
> > the last TRB (since IOC/LST are set only for the last TRB). As
> > per the logic in dwc3_gadget_ep_reclaim_completed_trb()
> > event->status is checked for IOC/LST bit and returns on the
> > first TRB. This leaves the remaining TRBs left unhandled.
> >
> > Similarly, if the gadget function enqueues an unaligned request
> > with sglist already in it, it should fail the same way, since we
> > will append another TRB to something that already uses more than
> > one TRB.
> >
> > To aviod this, this patch changes the code to check for IOC/LST
> > bits in TRB->ctrl instead.
> >
> > At a practical level, this patch resolves USB transfer stalls seen
> > with adb on dwc3 based HiKey960 after functionfs gadget added
> > scatter-gather support around v4.20.
> >
> > Cc: Felipe Balbi <balbi@...nel.org>
> > Cc: Yang Fei <fei.yang@...el.com>
> > Cc: Thinh Nguyen <thinhn@...opsys.com>
> > Cc: Tejas Joglekar <tejas.joglekar@...opsys.com>
> > Cc: Andrzej Pietrasiewicz <andrzej.p@...labora.com>
> > Cc: Jack Pham <jackp@...eaurora.org>
> > Cc: Todd Kjos <tkjos@...gle.com>
> > Cc: Greg KH <gregkh@...uxfoundation.org>
> > Cc: Linux USB List <linux-usb@...r.kernel.org>
> > Cc: stable <stable@...r.kernel.org>
> > Tested-by: Tejas Joglekar <tejas.joglekar@...opsys.com>
> > Reviewed-by: Thinh Nguyen <thinhn@...opsys.com>
> > Signed-off-by: Anurag Kumar Vulisha <anurag.kumar.vulisha@...inx.com>
> > [jstultz: forward ported to mainline, reworded commit log, reworked
> >  to only check trb->ctrl as suggested by Felipe]
> > Signed-off-by: John Stultz <john.stultz@...aro.org>
> > ---
> > v2:
> > * Rework to only check trb->ctrl as suggested by Felipe
> > * Reword the commit message to include more of Felipe's assessment
> > ---
> >  drivers/usb/dwc3/gadget.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
> > index 154f3f3e8cff..9a085eee1ae3 100644
> > --- a/drivers/usb/dwc3/gadget.c
> > +++ b/drivers/usb/dwc3/gadget.c
> > @@ -2420,7 +2420,8 @@ static int dwc3_gadget_ep_reclaim_completed_trb(struct dwc3_ep *dep,
> >       if (event->status & DEPEVT_STATUS_SHORT && !chain)
> >               return 1;
> >
> > -     if (event->status & DEPEVT_STATUS_IOC)
> > +     if ((trb->ctrl & DWC3_TRB_CTRL_IOC) ||
> > +         (trb->ctrl & DWC3_TRB_CTRL_LST))
>
> why the LST bit here? It wasn't there before. In fact, we never set LST
> in dwc3 anymore :-)

So, it was in the patch before, just on separate lines:
  https://lore.kernel.org/lkml/20200122222645.38805-2-john.stultz@linaro.org/

- if (event->status & DEPEVT_STATUS_IOC)
+ if ((event->status & DEPEVT_STATUS_IOC) &&
+    (trb->ctrl & DWC3_TRB_CTRL_IOC))
+ return 1;
+
+ if ((event->status & DEPEVT_STATUS_LST) &&
+    (trb->ctrl & DWC3_TRB_CTRL_LST))
  return 1;

So I just merged the two checks into one line. But I'm ok to drop the
CTRL_LST check if that really isn't used.  Let me know and I'll rework
and resend.

thanks
-john