Date:   Wed, 15 Jun 2022 18:13:26 +0000
From:   Marcel Ziswiler <marcel.ziswiler@...adex.com>
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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 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 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.

> > 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.

> Best regards,
> Krzysztof

[1] https://github.com/devicetree-org/dt-schema/blob/main/dtschema/schemas/clock/clock.yaml#L22

Cheers

Marcel

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