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From:   Alex Williams <alex.williams@ettus.com>
Date:   Fri, 15 Feb 2019 07:29:30 -0800
Message-ID: <CAJZzcDiv8BGDa8pj-2gP+BWiu=CfrsDi15xHr=UUFwCwE-E4zg@mail.gmail.com>
Subject: Re: [PATCH] i2c: cadence: Handle transfer_size rollover
To:     Shubhrajyoti Datta <shubhrajyoti.datta@gmail.com>
Cc:     mical.simek@xilinx.com, linux-arm-kernel@lists.infradead.org,
        linux-i2c@vger.kernel.org, linux-kernel@vger.kernel.org,
        Alex Williams <alex.williams@ni.com>
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On Fri, Feb 15, 2019 at 2:53 AM Shubhrajyoti Datta
<shubhrajyoti.datta@gmail.com> wrote:
>
> HI Alex,
>
> Thanks for the patch.
>
> On Fri, Feb 1, 2019 at 4:22 AM <alex.williams@ettus.com> wrote:
> >
> > From: Alex Williams <alex.williams@ni.com>
> >
> > Under certain conditions, Cadence's I2C controller's transfer_size
>
> Any help in reproducing the conditions would be appreciated
>
>
> > register will roll over and generate invalid read transactions. Before
> > this change, the ISR relied solely on the RXDV bit to determine when to
> > write more data to the user's buffer. The invalid read data would cause
> > overruns, smashing stacks and worse.
> >
> > This change stops the buffer writes to the requested boundary and
> > reports the error. The controller will be reset so normal transactions
> > may resume.
> >
> > Signed-off-by: Alex Williams <alex.williams@ni.com>


One possible related errata is here:
https://www.xilinx.com/support/answers/61664.html

In our case, we only needed to hammer on i2c to reproduce in a few
minutes, with a script like this:
while true
    do date
    cat /sys/class/gpio/gpio882/direction > /dev/null
    cat /sys/class/gpio/gpio883/direction > /dev/null
    cat /sys/class/gpio/gpio884/direction > /dev/null
    cat /sys/class/gpio/gpio885/direction > /dev/null
    cat /sys/class/gpio/gpio886/direction > /dev/null
    cat /sys/class/gpio/gpio887/direction > /dev/null
    cat /sys/class/gpio/gpio888/direction > /dev/null
    cat /sys/class/gpio/gpio889/direction > /dev/null
    cat /sys/class/gpio/gpio890/direction > /dev/null
    cat /sys/class/gpio/gpio891/direction > /dev/null
    cat /sys/class/gpio/gpio892/direction > /dev/null

    cat /sys/class/gpio/gpio894/direction > /dev/null
    cat /sys/class/gpio/gpio895/direction > /dev/null
    cat /sys/class/gpio/gpio896/direction > /dev/null
    cat /sys/class/gpio/gpio897/direction > /dev/null
    cat /sys/class/gpio/gpio898/direction > /dev/null
    cat /sys/class/gpio/gpio899/direction > /dev/null
    cat /sys/class/gpio/gpio900/direction > /dev/null
    cat /sys/class/gpio/gpio901/direction > /dev/null
    cat /sys/class/gpio/gpio902/direction > /dev/null
    cat /sys/class/gpio/gpio903/direction > /dev/null
    cat /sys/class/gpio/gpio904/direction > /dev/null
    cat /sys/class/gpio/gpio905/direction > /dev/null
done

In normal usage, we have code that sets up a number of i2c GPIO
expanders and pokes them for values as it initializes devices.
Occasionally, the transfer size register will roll over, and the ISR
will cause memory corruption, since it doesn't stop writing at the
requested boundary.