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

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Date:   Sat, 6 Mar 2021 01:04:01 -0800
From:   Wesley Cheng <wcheng@...eaurora.org>
To:     Thinh Nguyen <Thinh.Nguyen@...opsys.com>,
        John Stultz <john.stultz@...aro.org>,
        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>,
        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 1/8/2021 4:44 PM, Thinh Nguyen wrote:
> Hi,
> 
> John Stultz wrote:
>> 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://urldefense.com/v3/__https://lore.kernel.org/lkml/CALAqxLXdnaUfJKx0aN9xWwtfWVjMWigPpy2aqsNj56yvnbU80g@mail.gmail.com/__;!!A4F2R9G_pg!LNzuprAeg-O80SgolYkIkW4-ne-M-yLWCDUY9MygAIrQC398Z6gRJ9wnsnlqd3w$ 
>>>>
>>>> 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://urldefense.com/v3/__https://lore.kernel.org/lkml/20201021181803.79650-1-john.stultz@linaro.org/__;!!A4F2R9G_pg!LNzuprAeg-O80SgolYkIkW4-ne-M-yLWCDUY9MygAIrQC398Z6gRJ9wnRWITZfc$ 
>>
>> 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
> 
> A quirk would imply something is broken/diverged from the design right?
> But it's not the case here, and at least this is needed for HiKey960.
> Also, I think Rob will be ok with not adding 1 more quirk to the dwc3
> devicetree. :)
> 
> BR,
> Thinh
> 

Hi All,

Sorry for jumping in, but I checked the SNPS v1.90a databook, and that
seemed to remove the requirement for the GCTL.softreset before writing
to PRTCAPDIR.  Should we consider adding a controller version/IP check?

Thanks
Wesley Cheng

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