Re: [PATCH 2/9] dt-bindings: i2c: qcom-cci: add description of a vbus-supply property

[Vladimir Zapolskiy <vladimir.zapolskiy@linaro.org>]

On 2/7/22 4:39 PM, Mark Brown wrote:
> On Mon, Feb 07, 2022 at 04:08:01PM +0200, Vladimir Zapolskiy wrote:
>> On 2/4/22 9:32 PM, Mark Brown wrote:
> 
>>> Oh, good.  I forsee no problems here.  Probably this is something that
>>> should be in the I2C core if it's going to be dynamically managed,
>>> though just setting the supply as always on is probably more expedient.
> 
>> vbus-supply property has been added recently to another I2C master controller,
>> see commit c021087c43c8 ("dt-binding: i2c: mt65xx: add vbus-supply property").
> 
> Note that some devices do have supplies that I/O is referenced against
> and it's not clear that this isn't what's goin on here.
>
>> It serves right the same purpose, and its handling is going to be done in i2c
>> core, however since the latter is not yet completed, I would propose to add
>> the property to i2c-bus subnodes of QCOM CCI and its support in the driver,
>> later on both the property and its generic support would be better to see in
>> i2c core.
> 
> The bindings are ABI, it doesn't seem like a good idea to add new ABI as
> a temporary bodge.

The bindings are supposed to describe hardware, thus it's natural to extend
them, I believe there is a trilemma in this particular case:
1) add optional vbus-supply property to all I2C master controllers or I2C
    busses in case of multiple I2C busses managed by a single controller,
2) add optional vbus-supply property to all I2C slave devices,
3) ignore peculiarities of particular (multiple in fact) PCB designs and
    a necessity of adding a regulator finely described as a pull-up for I2C
    bus lines.

My assumption is that a decision should be generic for all similar cases,
Wolfram, could you share your point of view on the subject?

--
Best wishes,
Vladimir