linux-kernel - Re: i2c: core: report OF style module alias for devices registered via OF

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Date:   Fri, 9 Feb 2018 18:22:19 +0100
From:   Javier Martinez Canillas <javier@...hile0.org>
To:     Wolfram Sang <wsa@...-dreams.de>
Cc:     Dmitry Mastykin <mastichi@...il.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux I2C <linux-i2c@...r.kernel.org>,
        Javier Martinez Canillas <javierm@...hat.com>
Subject: Re: i2c: core: report OF style module alias for devices registered
 via OF

Hi Wolfram,

On Tue, Jan 16, 2018 at 3:11 PM, Javier Martinez Canillas
<javierm@...hat.com> wrote:
> 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@...hat.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.
>

Another gentle ping for this.

Best regards,
Javier