linux-kernel - Re: [PATCH 2/6] dt-bindings: regulator: Add reg-external-output binding

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Date:   Wed, 4 May 2022 14:35:08 -0700
From:   Zev Weiss <zev@...ilderbeest.net>
To:     Mark Brown <broonie@...nel.org>
Cc:     Liam Girdwood <lgirdwood@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        openbmc@...ts.ozlabs.org, MyungJoo Ham <myungjoo.ham@...sung.com>,
        Chanwoo Choi <cw00.choi@...sung.com>
Subject: Re: [PATCH 2/6] dt-bindings: regulator: Add reg-external-output
 binding

[Adding extcon maintainers...]

On Wed, May 04, 2022 at 01:49:12PM PDT, Mark Brown wrote:
>On Wed, May 04, 2022 at 01:33:58PM -0700, Zev Weiss wrote:
>> On Wed, May 04, 2022 at 05:55:53AM PDT, Mark Brown wrote:
>
>> > I think at a minimum anything like this would need some sort of
>> > representation of how the output physically appears so that people can
>> > work out how outputs are mapped to the hardware they see.
>
>> I don't quite understand what you're describing here -- could you elaborate
>> on what you mean by "how the output physically appears", and what that might
>> look like in a DT binding?
>
>For example if the output comes out on a socket then that socket should
>be described.
>

Okay -- in the case of an Open19 power shelf like the ahe-50dc, there 
are 50 instances of this, 48 of which are in four ganged connectors each 
with 12 pairs of pins, but two of which have their own dedicated little 
individual sockets.  The connectors are physically different, but 
they're all identical as far as software is concerned, so I'm not clear 
on why it would need to be expressed in any DT properties or the like.  
Or did you just mean explanatory free-form text in the description 
field?

>> > However we
>> > already have a subsystem for external connectors - extcon.  Perhaps this
>> > should be a regulator client in the extcon API?  It's common for
>> > connectors to include some sort of power provision so it seems like this
>> > would fit right in.
>
>> Interesting -- I wasn't previously aware of the extcon subsystem, thanks for
>> the pointer.  However, after looking at it a bit, I'm not sure I see how
>> it'd be applicable here, since it looks like it's built to handle hardware
>> that's at least sophisticated enough for software to tell whether or not
>> something's plugged in, which isn't the case here.  The connector is just a
>> ground pin and +12VDC pin, no presence-detection mechanism or anything else.
>> Outside of the regulator itself there's really no "device" there for
>> software to talk to or otherwise interact with at all.
>
>Sure, but there's no reason why it can't scale down to something
>simpler.  It's easier to support something simpler than have to extend
>to support something more complicated.

Alright, so would you suggest creating something like 
drivers/extcon/extcon-regulator-output.c, and just having its extcon 
functionality be something of a stub for now?


Thanks,
Zev