linux-kernel - Re: [RESEND PATCH v5 00/16] eeprom: at24: Add OF device ID table

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Date:   Wed, 30 Aug 2017 22:15:45 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Javier Martinez Canillas <javier@...hile0.org>
Cc:     Wolfram Sang <wsa@...-dreams.de>,
        Linux Kernel <linux-kernel@...r.kernel.org>,
        Rob Herring <robh@...nel.org>, Florian Larysch <fl@...1.de>,
        David Lechner <david@...hnology.com>,
        Rob Herring <robh+dt@...nel.org>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Sören Brinkmann <soren.brinkmann@...inx.com>,
        Simon Horman <horms@...ge.net.au>,
        Michal Simek <michal.simek@...inx.com>,
        Dinh Nguyen <dinguyen@...nel.org>,
        Russell King <linux@...linux.org.uk>,
        Will Deacon <will.deacon@....com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        Sekhar Nori <nsekhar@...com>, Scott Wood <oss@...error.net>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Joachim Eastwood <manabian@...il.com>,
        Mark Rutland <mark.rutland@....com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Santosh Shilimkar <ssantosh@...nel.org>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        Paul Mackerras <paulus@...ba.org>,
        Magnus Damm <magnus.damm@...il.com>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        Uwe Kleine-König <kernel@...gutronix.de>,
        Linux I2C <linux-i2c@...r.kernel.org>
Subject: Re: [RESEND PATCH v5 00/16] eeprom: at24: Add OF device ID table

Hi Javier,

On Wed, Aug 30, 2017 at 9:57 PM, Javier Martinez Canillas
<javier@...hile0.org> wrote:
>> I think we should talk about the same case: Let me repeat what I did:
>>
>> 1) I added your patch "eeprom: at24: Add OF device ID table"
>> 2) I added an EEPROM node to an I2C
>>
>> +       eeprom@50 {
>> +               compatible = "renesas,24c01";
>> +               reg = <0x50>;
>> +       };
>>
>> -> no at24 binding to the device
>>
>> 3) I revert your patch
>>
>> -> at24 binding to the device
>>
>
> I've tested this and you are right, it fails...
>
> The problem is that the patch also changes how the driver obtains the
> EEPROM parameters (the magic value in the entry's data field).
>
> So even when module autoload and device / driver matching works, the
> driver probe function fails because if (client->dev.of_node) the
> driver attempts to get the entry data using
> of_device_get_match_data(), which is obviously wrong since the
> compatible string in the dev node isn't present in the OF table.
>
> The id->driver_data from the I2C table should be used instead since
> that's the table that matches in this case.
>
> One option is to fallback to id->driver_data if
> of_device_get_match_data() fails, but that's just an (ugly)
> workaround. So I agree with you that the best option is to wait for
> the DTS patches to land first.

Which means new kernels won't work with old DTBs. Oops...
I'm afraid that needs to be fixed.  People care about DTB backward
compatibility on many platforms.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds