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

John Keeping
2022-07-13T11:41:16Z

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@synopsys.com>
> > Signed-off-by: Wesley Cheng <quic_wcheng@quicinc.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);

?