linux-kernel - Re: [PATCH 00/13] rtc: Add OF device table to I2C drivers that are missing it

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Date:   Fri, 3 Mar 2017 12:27:23 -0300
From:   Javier Martinez Canillas <javier@....samsung.com>
To:     Alexandre Belloni <alexandre.belloni@...e-electrons.com>
Cc:     linux-kernel@...r.kernel.org, rtc-linux@...glegroups.com,
        Alessandro Zummo <a.zummo@...ertech.it>
Subject: Re: [PATCH 00/13] rtc: Add OF device table to I2C drivers that are
 missing it

Hello Alexandre,

On 03/03/2017 12:01 PM, Alexandre Belloni wrote:
> Hi,
> 
> On 03/03/2017 at 11:29:11 -0300, Javier Martinez Canillas wrote:
>> This series add OF device ID tables to RTC I2C drivers whose devices are
>> either used in Device Tree source files or are listed in binding docs as
>> a compatible string.
>>
>> That's done because the plan is to change the I2C core to report proper OF
>> modaliases instead of always reporting a MODALIAS=i2c:<foo> regardless if
>> a device was registered via DT or using the legacy platform data.
>>
> 
> Doesn't that break the DT ABI for all i2c devices? A lot of people are
> getting the vendor wrong in the compatible string and because the i2c
> core doesn't care, the driver is still probed. Dropping that will break
> all those DTBs.
> Or will that only affect module autoload?
> 

The change will only be for module autoload. The I2C core will still attempt
to match the I2C device ID table as a fallback if fails to match the OF one.
So there's no change in the match logic for drivers that do the wrong thing.

If someone is using a wrong vendor prefix and the DT can't be changed, then
an entry in the OF device ID table has to be added for "wrong_vendor,device"
so the MODALIAS uevent can be "of:N*T*wrong_vendor,device".

This is the RFC patch for the I2C core so you get a better idea:

https://patchwork.kernel.org/patch/6903981/

Best regards,
-- 
Javier Martinez Canillas
Open Source Group
Samsung Research America