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

From: John Stultz <john.stultz@linaro.org>
To: Felipe Balbi <balbi@kernel.org>
Cc: lkml <linux-kernel@vger.kernel.org>,
	Yu Chen <chenyu56@huawei.com>,
	Tejas Joglekar <tejas.joglekar@synopsys.com>,
	Yang Fei <fei.yang@intel.com>,
	YongQin Liu <yongqin.liu@linaro.org>,
	Andrzej Pietrasiewicz <andrzej.p@collabora.com>,
	Thinh Nguyen <thinhn@synopsys.com>,
	Jun Li <lijun.kernel@gmail.com>,
	Mauro Carvalho Chehab <mchehab+huawei@kernel.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Linux USB List <linux-usb@vger.kernel.org>,
	Heikki Krogerus <heikki.krogerus@linux.intel.com>,
	Roger Quadros <rogerq@ti.com>
Subject: Re: [PATCH v3 1/2] usb: dwc3: Trigger a GCTL soft reset when switching modes in DRD
Date: Fri, 8 Jan 2021 11:18:32 -0800	[thread overview]
Message-ID: <CALAqxLWdWj9=a-7NGDzJyrfyRABwKnJM7EQo3Zm+k9JqAhPz+g@mail.gmail.com> (raw)
In-Reply-To: <87bldzwr6x.fsf@kernel.org>

On Fri, Jan 8, 2021 at 4:26 AM Felipe Balbi <balbi@kernel.org> wrote:
>
>
> Hi,
>
> John Stultz <john.stultz@linaro.org> writes:
> > From: Yu Chen <chenyu56@huawei.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@kernel.org>
> > Cc: Tejas Joglekar <tejas.joglekar@synopsys.com>
> > Cc: Yang Fei <fei.yang@intel.com>
> > Cc: YongQin Liu <yongqin.liu@linaro.org>
> > Cc: Andrzej Pietrasiewicz <andrzej.p@collabora.com>
> > Cc: Thinh Nguyen <thinhn@synopsys.com>
> > Cc: Jun Li <lijun.kernel@gmail.com>
> > Cc: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
> > Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> > Cc: linux-usb@vger.kernel.org
> > Signed-off-by: Yu Chen <chenyu56@huawei.com>
> > Signed-off-by: John Stultz <john.stultz@linaro.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