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Subject: Re: i2c: core: report OF style module alias for devices registered
 via OF
To: Dmitry Mastykin <mastichi@gmail.com>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Wolfram Sang <wsa@the-dreams.de>, linux-i2c@vger.kernel.org
References: <CALieaeczi5iZPgKVdHw1B3ouyWcd2U_cqPzEYqvT+8JW4Uwi3A@mail.gmail.com>
From: Javier Martinez Canillas <javierm@redhat.com>
Message-ID: <a81cf234-f103-1787-6a4a-fc59bb50cb4d@redhat.com>
Date: Tue, 16 Jan 2018 15:11:32 +0100
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Hello Dmitry,

On 01/16/2018 02:55 PM, Dmitry Mastykin wrote:
> On Sun, 3 Dec 2017 22:40:50 +0100, Javier Martinez Canillas
> <javierm@redhat.com> wrote:
> 
>> The buses should honor the firmware interface used to register the device,
>> but the I2C core reports a MODALIAS of the form i2c:<device> even for I2C
>> devices registered via OF.
>>
>> This means that user-space will never get an OF stype uevent MODALIAS even
>> when the drivers modules contain aliases exported from both the I2C and OF
>> device ID tables. For example, an Atmel maXTouch Touchscreen registered by
>> a DT node with compatible "atmel,maxtouch" has the following module alias:
>>
>> $ cat /sys/class/i2c-adapter/i2c-8/8-004b/modalias
>> i2c:maxtouch
>>
>> So udev won't be able to auto-load a module for an OF-only device driver.
>> Many OF-only drivers duplicate the OF device ID table entries in an I2C ID
>> table only has a workaround for how the I2C core reports the module alias.
>>
>> This patch changes the I2C core to report an OF related MODALIAS uevent if
>> the device was registered via OF. So for the previous example, after this
>> patch, the reported MODALIAS for the Atmel maXTouch will be the following:
>>
>> $ cat /sys/class/i2c-adapter/i2c-8/8-004b/modalias
>> of:NtrackpadT<NULL>Catmel,maxtouch
>>
>> NOTE: This patch may break out-of-tree drivers that were relying on this
>>       behavior, and only had an I2C device ID table even when the device
>>       was registered via OF. There are no remaining drivers in mainline
>>       that do this, but out-of-tree drivers have to be fixed and define
>>       a proper OF device ID table to have module auto-loading working.
>>
> 
> Hello Javier,
> thank you for your patch!
>

Thanks a lot for testing!

Hopefully Wolfram will review/merge this soon, otherwise in the meantime drivers
are going to add I2C device ID tables just as a workaround or new drivers won't
include a OF device ID tables since these aren't really required today.

I made sure that all the drivers in mainline were fixed before posting this, but
haven't checked since then.

Best regards,
-- 
Javier Martinez Canillas
Software Engineer - Desktop Hardware Enablement
Red Hat