linux-kernel - Re: [PATCH v2 5/5] usb: dwc3: gadget: Increase DWC3 controller halt timeout

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Date:   Wed, 13 Jul 2022 12:40:53 +0100
From:   John Keeping <john@...anate.com>
To:     Jack Pham <quic_jackp@...cinc.com>
Cc:     Wesley Cheng <quic_wcheng@...cinc.com>, balbi@...nel.org,
        gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org,
        linux-usb@...r.kernel.org, Thinh.Nguyen@...opsys.com
Subject: Re: [PATCH v2 5/5] usb: dwc3: gadget: Increase DWC3 controller halt
 timeout

On Tue, Jul 12, 2022 at 07:56:43PM -0700, Jack Pham wrote:
> Hi Wesley,
> 
> On Tue, Jul 12, 2022 at 05:35:23PM -0700, Wesley Cheng wrote:
> > Since EP0 transactions need to be completed before the controller halt
> > sequence is finished, this may take some time depending on the host and the
> > enabled functions.  Increase the controller halt timeout, so that we give
> > the controller sufficient time to handle EP0 transfers.
> > 
> > Fixes: 861c010a2ee1 ("usb: dwc3: gadget: Refactor pullup()")
> > Suggested-by: Thinh Nguyen <Thinh.Nguyen@...opsys.com>
> > Signed-off-by: Wesley Cheng <quic_wcheng@...cinc.com>
> > ---
> > Link:
> >   https://lore.kernel.org/linux-usb/4988ed34-04a4-060a-ccef-f57790f76a2b@synopsys.com/
> > 
> >  drivers/usb/dwc3/gadget.c | 1 +
> >  1 file changed, 1 insertion(+)
> > 
> > diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
> > index 41b7007358de..e32d7293c447 100644
> > --- a/drivers/usb/dwc3/gadget.c
> > +++ b/drivers/usb/dwc3/gadget.c
> > @@ -2476,6 +2476,7 @@ static int dwc3_gadget_run_stop(struct dwc3 *dwc, int is_on, int suspend)
> >  	dwc3_gadget_dctl_write_safe(dwc, reg);
> >  
> >  	do {
> > +		msleep(1);
> 
> Be aware that this probably won't sleep for *just* 1ms.  From
> Documentation/timers/timers-howto.rst:
> 
> 	msleep(1~20) may not do what the caller intends, and
> 	will often sleep longer (~20 ms actual sleep for any
> 	value given in the 1~20ms range). In many cases this
> 	is not the desired behavior.
> 
> So with timeout==500 this loop could very well end up iterating for up
> to 10 seconds.  Granted this shouldn't be called from any atomic context
> but just wanted to make sure that the effective increase in timeout as
> $SUBJECT intends is made clear here and that it's not overly generous.
> 
> >  		reg = dwc3_readl(dwc->regs, DWC3_DSTS);
> >  		reg &= DWC3_DSTS_DEVCTRLHLT;
> >  	} while (--timeout && !(!is_on ^ !reg));

Does it make sense to convert this loop to use read_poll_timeout() and
make the timeout explicit, something like:

	ret = read_poll_timeout(dwc3_readl, reg, !(!is_on ^ !(reg & DWC3_DSTS_DEVCTRLHLT)),
				100, timeout * USEC_PER_MSEC, true, dwc->regs, DWC3_DSTS);

?