linux-kernel - Re: [PATCH] eeprom: at24: correctly set the size for at24mac402

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Date:   Tue, 28 Nov 2017 11:44:07 +0100
From:   Bartosz Golaszewski <brgl@...ev.pl>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Heiner Kallweit <hkallweit1@...il.com>,
        Claudiu Beznea <Claudiu.Beznea@...rochip.com>,
        linux-i2c <linux-i2c@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        stable@...r.kernel.org
Subject: Re: [PATCH] eeprom: at24: correctly set the size for at24mac402

2017-11-28 11:25 GMT+01:00 Andy Shevchenko <andy.shevchenko@...il.com>:
> On Mon, Nov 27, 2017 at 11:06 PM, Bartosz Golaszewski <brgl@...ev.pl> wrote:
>> There's an ilog2() expansion in AT24_DEVICE_MAGIC() which rounds down
>> the actual size of EUI-48 byte array in at24mac402 eeproms to 4 from 6,
>> making it impossible to read it all.
>>
>> Fix it by manually adjusting the value in probe().
>>
>> This patch contains a temporary fix that is suitable for stable
>> branches. Eventually we'll probably remove the call to ilog2() while
>> converting the magic values to actual structs.
>
>> +       /*
>> +        * REVISIT: the size of the EUI-48 byte array is 6 in at24mac402, while
>> +        * the call to ilog2() in AT24_DEVICE_MAGIC() rounds it down to 4.
>> +        *
>> +        * Eventually we'll get rid of the magic values altoghether in favor of
>> +        * real structs, but for now just manually set the right size.
>> +        */
>> +       if (chip.flags & AT24_FLAG_MAC && chip.byte_len == 4)
>
> I didn't check, but do we need to test for len == 4 at all?
>
>> +               chip.byte_len = 6;
>
> --
> With Best Regards,
> Andy Shevchenko

Yes, because the fix is only relevant for at24mac402 whose MAC byte
array is 6 bytes long, while the one in at24mac602 is 8 bytes and the
driver doesn't truncate the byte_len for it.

Thanks,
Bartosz