linux-kernel - Re: [PATCH v3 1/2] usb: dwc3: Trigger a GCTL soft reset when switching modes in DRD

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Date:   Fri, 8 Jan 2021 11:18:32 -0800
From:   John Stultz <john.stultz@...aro.org>
To:     Felipe Balbi <balbi@...nel.org>
Cc:     lkml <linux-kernel@...r.kernel.org>, Yu Chen <chenyu56@...wei.com>,
        Tejas Joglekar <tejas.joglekar@...opsys.com>,
        Yang Fei <fei.yang@...el.com>,
        YongQin Liu <yongqin.liu@...aro.org>,
        Andrzej Pietrasiewicz <andrzej.p@...labora.com>,
        Thinh Nguyen <thinhn@...opsys.com>,
        Jun Li <lijun.kernel@...il.com>,
        Mauro Carvalho Chehab <mchehab+huawei@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Linux USB List <linux-usb@...r.kernel.org>,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        Roger Quadros <rogerq@...com>
Subject: Re: [PATCH v3 1/2] usb: dwc3: Trigger a GCTL soft reset when
 switching modes in DRD

On Fri, Jan 8, 2021 at 4:26 AM Felipe Balbi <balbi@...nel.org> wrote:
>
>
> Hi,
>
> John Stultz <john.stultz@...aro.org> writes:
> > From: Yu Chen <chenyu56@...wei.com>
> >
> > Just resending this, as discussion died out a bit and I'm not
> > sure how to make further progress. See here for debug data that
> > was requested last time around:
> >   https://lore.kernel.org/lkml/CALAqxLXdnaUfJKx0aN9xWwtfWVjMWigPpy2aqsNj56yvnbU80g@mail.gmail.com/
> >
> > With the current dwc3 code on the HiKey960 we often see the
> > COREIDLE flag get stuck off in __dwc3_gadget_start(), which
> > seems to prevent the reset irq and causes the USB gadget to
> > fail to initialize.
> >
> > We had seen occasional initialization failures with older
> > kernels but with recent 5.x era kernels it seemed to be becoming
> > much more common, so I dug back through some older trees and
> > realized I dropped this quirk from Yu Chen during upstreaming
> > as I couldn't provide a proper rational for it and it didn't
> > seem to be necessary. I now realize I was wrong.
> >
> > After resubmitting the quirk, Thinh Nguyen pointed out that it
> > shouldn't be a quirk at all and it is actually mentioned in the
> > programming guide that it should be done when switching modes
> > in DRD.
> >
> > So, to avoid these !COREIDLE lockups seen on HiKey960, this
> > patch issues GCTL soft reset when switching modes if the
> > controller is in DRD mode.
> >
> > Cc: Felipe Balbi <balbi@...nel.org>
> > Cc: Tejas Joglekar <tejas.joglekar@...opsys.com>
> > Cc: Yang Fei <fei.yang@...el.com>
> > Cc: YongQin Liu <yongqin.liu@...aro.org>
> > Cc: Andrzej Pietrasiewicz <andrzej.p@...labora.com>
> > Cc: Thinh Nguyen <thinhn@...opsys.com>
> > Cc: Jun Li <lijun.kernel@...il.com>
> > Cc: Mauro Carvalho Chehab <mchehab+huawei@...nel.org>
> > Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> > Cc: linux-usb@...r.kernel.org
> > Signed-off-by: Yu Chen <chenyu56@...wei.com>
> > Signed-off-by: John Stultz <john.stultz@...aro.org>
> > ---
> > v2:
> > * Rework to always call the GCTL soft reset in DRD mode,
> >   rather then using a quirk as suggested by Thinh Nguyen
> >
> > v3:
> > * Move GCTL soft reset under the spinlock as suggested by
> >   Thinh Nguyen
>
> Because this is such an invasive change, I would prefer that we get
> Tested-By tags from a good fraction of the users before applying these
> two changes.

I'm happy to reach out to folks to try to get that. Though I'm
wondering if it would be better to put it behind a dts quirk flag, as
originally proposed?
   https://lore.kernel.org/lkml/20201021181803.79650-1-john.stultz@linaro.org/

That way folks can enable it for devices as they need?

Again, I'm not trying to force this in as-is, just mostly sending it
out again for discussion to understand what other approach might work.

thanks
-john