linux-kernel - Re: [PATCH v2 3/3] dt-bindings: mfd: stpmic1: add fsl,pmic-poweroff property

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Message-ID: <20230524-cider-unarmored-b1141db1030b@spud>
Date:   Wed, 24 May 2023 20:57:16 +0100
From:   Conor Dooley <conor@...nel.org>
To:     Sean Nyekjaer <sean@...nix.com>
Cc:     Conor Dooley <conor.dooley@...rochip.com>, robh+dt@...nel.org,
        Lee Jones <lee@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        pascal Paillet <p.paillet@...s.st.com>,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 3/3] dt-bindings: mfd: stpmic1: add fsl,pmic-poweroff
 property

Hey Sean, Lee,

On Wed, May 24, 2023 at 12:30:59PM +0200, Sean Nyekjaer wrote:
> > On 24 May 2023, at 12.08, Conor Dooley <conor.dooley@...rochip.com> wrote:
> > On Wed, May 24, 2023 at 10:16:13AM +0200, Sean Nyekjær wrote:
> >>> On 23 May 2023, at 19.29, Conor Dooley <conor@...nel.org> wrote:
> >>> On Tue, May 23, 2023 at 11:55:50AM +0200, Sean Nyekjær wrote:
> >>>>> On 16 May 2023, at 20.06, Conor Dooley <conor@...nel.org> wrote:
> >>>>> On Tue, May 16, 2023 at 03:22:24PM +0200, Sean Nyekjaer wrote:

> >>>>>> +  st,pmic-poweroff:
> >>>>>> +    $ref: /schemas/types.yaml#/definitions/flag
> >>>>>> +    description: |
> >>>>>> +      if present, configure the PMIC to shutdown all power rails when
> >>>>>> +      power off sequence have finished.
> >>>>>> +      Use this option if the SoC should be powered off by external power management
> >>>>>> +      IC (PMIC).
> >>>>> 
> >>>>> Just reading this description, this is sounding quite like a "software
> >>>>> behaviour" type of property, which are not permitted, rather than
> >>>>> describing some element of the hardware. Clearly you are trying to solve
> >>>>> an actual problem though, so try re-phrasing the description (and
> >>>>> property name) to focus on what exact hardware configuration it is that
> >>>>> you are trying to special-case.
> >>>>> Krzysztof suggested that the samsung,s2mps11-acokb-ground property in
> >>>>> samsung,s2mps11.yaml is addressing a similar problem, so that could be
> >>>>> good to look at.

> >>> The description for the property that Krzysztof mentioned is
> >>> samsung,s2mps11-acokb-ground:
> >>>   description: |
> >>>     Indicates that ACOKB pin of S2MPS11 PMIC is connected to the ground so
> >>>     the PMIC must manually set PWRHOLD bit in CTRL1 register to turn off the
> >>>     power. Usually the ACOKB is pulled up to VBATT so when PWRHOLD pin goes
> >>>     low, the rising ACOKB will trigger power off.
> >>> 
> >>> In other words, I am asking what (abnormal?) scenario there is that means
> >>> you need the property, rather than what setting the property does.
> >>> Or am I totally off, and this is the only way this PMIC works?
> >> 
> >> Indicates that the power management IC (PMIC) turn-off condition is met
> >> by setting the SWOFF bit in the main control register (MAIN_CR) register.
> >> Turn-off condition can still be reached by the PONKEY input.
> >> 
> >> ?
> >> 
> >> I must admit I’m somewhat lost here :)
> > 
> > Sorry about that. I'm trying to understand what is different about your
> > hardware that it needs the property rather than what adding the property
> > does. If you look at the samsung one, it describes both the
> > configuration of the hardware ("ACOKB pin of S2MPS11 PMIC is connected to
> > the ground") and how that is different from normal ("Usually the ACOKB is
> > pulled up to VBATT so when PWRHOLD pin goes low, the rising ACOKB will
> > trigger power off.")
> > 
> > Looking at your datasheet, you don't have such a pin though - just the
> > sw poweroff bit & the PONKEY stuff. My angle is just that I am trying
> > to figure out why you need this property when it has not been needed
> > before. Or why you would not always want to "shutdown all power rails
> > when power-off sequence have finished". I'm sorry if these are silly
> > questions.
> > 
> 
> No silly questions, maybe they trick me to come up with the correct answer :D
> 
> Basically without this, you won’t be able to power off the system
> other than hitting the PONKEY.
> So it’s a new feature that wasn’t supported before.
> Maybe this feature should not be optional?

Yeah, I suppose that is the rabbit-hole that the silly questions lead
down. I don't know the answer to that though. Maybe Lee does?

> If st,pmic-poweroff == true:
> System will power off as the last step in the power off sequence.
> If st,pmic-powerof == false:
> System will reboot in the last step in the power off sequence.
> 
> I thought of this, as an always on system failsafe.
> 
> /Sean

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