Message-ID: <b21dab64-1e5b-eaab-2e74-e95a22ca6e82@linaro.org>
Date:   Wed, 15 Jun 2022 13:48:20 -0700
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Marcel Ziswiler <marcel.ziswiler@...adex.com>,
        "max.oss.09@...il.com" <max.oss.09@...il.com>,
        "geert@...ux-m68k.org" <geert@...ux-m68k.org>
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        "broonie@...nel.org" <broonie@...nel.org>,
        Francesco Dolcini <francesco.dolcini@...adex.com>,
        "robh@...nel.org" <robh@...nel.org>,
        "krzysztof.kozlowski+dt@...aro.org" 
        <krzysztof.kozlowski+dt@...aro.org>,
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        <linux-arm-kernel@...ts.infradead.org>,
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        Max Krummenacher <max.krummenacher@...adex.com>
Subject: Re: [PATCH v1 0/5] power: domain: Add driver for a PM domain provider
 which controls

On 15/06/2022 11:13, Marcel Ziswiler wrote:
> On Wed, 2022-06-15 at 10:37 -0700, Krzysztof Kozlowski wrote:
>> On 15/06/2022 10:31, Marcel Ziswiler wrote:
>>> Hi
>>>
>>> On Wed, 2022-06-15 at 10:15 -0700, Krzysztof Kozlowski wrote:
>>>> On 15/06/2022 09:10, Max Krummenacher wrote:
>>>>> Hi
>>>>>
>>>>> On Tue, Jun 14, 2022 at 9:22 AM Geert Uytterhoeven <geert@...ux-m68k.org> wrote:
>>>>>>
>>>>>> Hi Rob,
>>>>>>
>>>>>> On Mon, Jun 13, 2022 at 9:15 PM Rob Herring <robh@...nel.org> wrote:
>>>>>>> On Thu, Jun 09, 2022 at 05:08:46PM +0200, Max Krummenacher wrote:
>>>>>>>> From: Max Krummenacher <max.krummenacher@...adex.com>
>>>>>>>>
>>>>>>>> its power enable by using a regulator.
>>>>>>>>
>>>>>>>> The currently implemented PM domain providers are all specific to
>>>>>>>> a particular system on chip.
>>>>>>>
>>>>>>> Yes, power domains tend to be specific to an SoC... 'power-domains' is
>>>>>>> supposed to be power islands in a chip. Linux 'PM domains' can be
>>>>>>> anything...
>>>>>
>>>>> I don't see why such power islands should be restricted to a SoC. You can
>>>>> build the exact same idea on a PCB or even more modular designs.
>>>>
>>>> In the SoC these power islands are more-or-less defined. These are real
>>>> regions gated by some control knob.
>>>>
>>>> Calling few devices on a board "power domain" does not make it a power
>>>> domain. There is no grouping, there is no control knob.
>>>>
>>>> Aren't you now re-implementing regulator supplies? How is this different
>>>> than existing supplies?
>>>
>>> I believe the biggest difference between power-domains and regulator-supplies lays in the former being
>>> driver
>>> agnostic while the later is driver specific. 
>>
>> That's one way to look, but the other way (matching the bindings
>> purpose) is to look at hardware. You have physical wire / voltage rail
>> supply - use regulator supply. In the terms of the hardware - what is
>> that power domain? It's a concept, not a physical object.
> 
> Well, but how can that concept then exist within the SoC but not outside? I don't get it. Isn't it just the
> exact same physical power gating thingy whether inside the SoC or on a PCB?
> 
>>> Meaning with power-domains one can just add such arbitrary
>>> structure to the device tree without any further driver specific changes/handling required. While with
>>> regulator-supplies each and every driver actually needs to have driver specific handling thereof added. Or
>>> do I
>>> miss anything?
>>
>> Thanks for clarification but I am not sure if it matches the purpose of
>> bindings and DTS. You can change the implementation as well to have
>> implicit regulators. No need for new bindings for that.
> 
> Okay, maybe that would also work, of course. So basically add a new binding 

That I did not propose. :) We have a binding for regulator supplies so
you do no need a new one.

> which allows adding regulators to
> arbitrary nodes which then will be generically handled by e.g. runtime PM. Almost something like assigned-
> clocks [1] you mean? I guess that could work. Remember that's why Max posted it as an RFC to get such feedback.
> Thanks for further refining those ideas.

DTS and bindings describe here the hardware, so focus on that. Device is
supplied by some regulator which I assume can be controlled by GPIO. I
don't think you need new bindings for that.

Implementation of bindings, so Linux driver, is different thing.

> 
>>> We are really trying to model something where a single GPIO pin (via a GPIO regulator or whatever) can
>>> control
>>> power to a variety of on-board peripherals. And, of course, we envision runtime PM actually making use of
>>> it
>>> e.g. when doing suspend/resume.
>>
>> And this GPIO pin controls what? Some power switch which cuts the power
>> of one regulator or many?
> 
> Well, that doesn't really matter. Resp. this part one should be able to sufficiently model using whatever
> available regulator lore we already have (e.g. whatever delays/times).
> 
>> If many different regulators, how do you
>> handle small differences in ramp up time?
> 
> Well, I don't think this is any different to any other regulator(s), not? Them HW folks will just need to tell
> us some reasonable numbers for those delays/times.

Probably... I just wonder how that would work in practice.


Best regards,
Krzysztof

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