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Subject: Re: [REGRESSION] usb: gadget: f_fs: Allow scatter-gather buffers
To:     John Stultz <john.stultz@linaro.org>,
        Felipe Balbi <balbi@kernel.org>
Cc:     "Yang, Fei" <fei.yang@intel.com>,
        Bjorn Andersson <bjorn.andersson@linaro.org>,
        Chen Yu <chenyu56@huawei.com>,
        lkml <linux-kernel@vger.kernel.org>,
        Linux USB List <linux-usb@vger.kernel.org>,
        Amit Pundir <amit.pundir@linaro.org>,
        Marek Szyprowski <m.szyprowski@samsung.com>
References: <CALAqxLUMRaNxwTUi9QS7-Cy-Ve4+vteBm8-jW4yzZg_QTJVChA@mail.gmail.com>
From:   Andrzej Pietrasiewicz <andrzejtp2010@gmail.com>
Message-ID: <5d58059c-1b10-665f-983b-a1d018a30d1f@gmail.com>
Date:   Wed, 8 May 2019 09:01:27 +0200
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Hi John,

+= Marek

W dniu 08.05.2019 o 04:18, John Stultz pisze:
> Since commit 772a7a724f69 ("usb: gadget: f_fs: Allow scatter-gather
> buffers"), I've been seeing trouble with adb transfers in Android on
> HiKey960, HiKey and now Dragonboard 845c.
> 
> Sometimes things crash, but often the transfers just stop w/o any
> obvious error messages.
> 
> Initially I thought it was an issue with the HiKey960 dwc3 usb patches
> being upstreamed, and was using the following hack workaround:
>    https://git.linaro.org/people/john.stultz/android-dev.git/commit/?h=dev/hikey960-5.1&id=dcdadaaec9db7a7b78ea9b838dd1453359a2f388
> 
> Then dwc2 added sg support, and I ended up having to revert it to get
> by on HiKey:
>    https://git.linaro.org/people/john.stultz/android-dev.git/commit/?h=dev/hikey-5.1&id=6e91b4c7bd1e94bdd835263403c53e85a677b848
> 
> (See thread here: https://lkml.org/lkml/2019/3/8/765)
> 
> And now I've reproduced the same issue (with the same dwc3 workaround)
> on the already upstream code for Dragonboard 845c.
> 
> Fei Yang has also reached out and mentioned he was seeing similar
> problems with the f_fs sg support.
> 
> Andrzej: Do you have any ideas or suggestions on this? I'm happy to
> test or run any debug patches, if it would help narrow the issue down.
> 

There is a patch:

https://www.spinics.net/lists/linux-usb/msg178536.html
https://www.spinics.net/lists/linux-usb/msg179653.html

which fixes a subtle bug, but hasn't been applied yet.

Can you please try it?

> If not, should we consider reverting the f_fs sg support?
> 

Andrzej