linux-kernel - Re: [PATCH v3 3/3] nfc: trf7970a: Prevent repeated polling from crashing the kernel

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Message-ID: <CAO7Z3WK5pF+q0vAoPPie8wXYQPigpGd7W8uQiGSgN79z4=W9uQ@mail.gmail.com>
Date:   Tue, 3 Jan 2017 13:35:18 -0500
From:   Geoff Lansberry <geoff@...ee.com>
To:     Mark Greer <mgreer@...malcreek.com>
Cc:     linux-wireless <linux-wireless@...r.kernel.org>,
        Lauro Ramos Venancio <lauro.venancio@...nbossa.org>,
        Aloisio Almeida Jr <aloisio.almeida@...nbossa.org>,
        Samuel Ortiz <sameo@...ux.intel.com>, robh+dt@...nel.org,
        mark.rutland@....com, netdev@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        Justin Bronder <justin@...ee.com>,
        Jaret Cantu <jaret.cantu@...esys.com>
Subject: Re: [PATCH v3 3/3] nfc: trf7970a: Prevent repeated polling from
 crashing the kernel

On Tue, Jan 3, 2017 at 11:33 AM, Mark Greer <mgreer@...malcreek.com> wrote:
> [Please stop top-posting.  Bottom-post only to these lists.]

Sorry; gmail keeps baiting me to do it...

>
> Hi Geoff & happy new year.
>
> On Tue, Dec 27, 2016 at 09:18:32AM -0500, Geoff Lansberry wrote:
>> Mark - I will split this off soon.
>
> OK

Thanks for the reminder!

>
>> In the meantime - here is some more info about how we use it.
>>
>> We do use NFC structures.    I did find an interesting clue in that
>> there are certain bottles that cause neard to segfault,  I'm not sure
>> what is different about them.  We write a string, like
>> "coppola_chardonnay_2015" to the bottles.
>
> Off the top of my head, it could be the length of the text.
> It would be useful to compare the data that works to the data
> that doesn't work.  Can you install NXP's 'TagInfo' app on a
> smartphone and scan tags with working & non-working data?
> You can email the data from the app to yourself, edit out
> the cruft, and share here.

The data is always the same - and the tags are all the same.  Only
difference is that the tag is physically different, and perhaps
orientation; distance from antenna to tag is fixed.  I can't even
write the tags at all, so reading them will show blank.   Also a minor
but significant detail, is that the tags are embedded in such a way
that the phone cannot get close enough to them to connect.

>
>> Come to think of it, I
>> haven't done anything special to make that an ndef record, just
>> assumed that it would happen by default, I'll look into this further.
>
> If you wrote the data using neard, it will be NDEF formatted.
> Since it is working this well, it is virtually guaranteed that
> the data is NDEF formatted.

OK, good.

>
>>   Also, I've been running neard with --plugin nfctype2. Just in case
>> the problem was happening due to cycling through other tag types.   It
>> didn't seem to make any difference, but I have not gone back to
>> default.
>
> Good to know, thanks.
>
> Mark
> --