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Subject: Re: [PATCH v2 3/3] dt-bindings: mfd: stpmic1: add fsl,pmic-poweroff
 property
From:   Sean Nyekjaer <sean@geanix.com>
In-Reply-To: <20230524-ellipse-dagger-72f850253ea0@wendy>
Date:   Wed, 24 May 2023 12:30:59 +0200
Cc:     Conor Dooley <conor@kernel.org>, robh+dt@kernel.org,
        Lee Jones <lee@kernel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        Conor Dooley <conor+dt@kernel.org>,
        pascal Paillet <p.paillet@foss.st.com>,
        devicetree@vger.kernel.org, linux-kernel@vger.kernel.org
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References: <20230516132225.3012541-1-sean@geanix.com>
 <20230516132225.3012541-3-sean@geanix.com>
 <20230516-footprint-handoff-bcd553ff6146@spud>
 <9B1EE405-77D3-4980-9A13-9D4F87C1A64F@geanix.com>
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To:     Conor Dooley <conor.dooley@microchip.com>
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> On 24 May 2023, at 12.08, Conor Dooley <conor.dooley@microchip.com> =
wrote:
>=20
> On Wed, May 24, 2023 at 10:16:13AM +0200, Sean Nyekj=C3=A6r wrote:
>> Hi Conor,
>>=20
>>> On 23 May 2023, at 19.29, Conor Dooley <conor@kernel.org> wrote:
>>>=20
>>> On Tue, May 23, 2023 at 11:55:50AM +0200, Sean Nyekj=C3=A6r wrote:
>>>>> On 16 May 2023, at 20.06, Conor Dooley <conor@kernel.org> wrote:
>>>>> On Tue, May 16, 2023 at 03:22:24PM +0200, Sean Nyekjaer wrote:
>>>>>> Document the new optional "fsl,pmic-poweroff" property.
>>>>>>=20
>>>>>> Signed-off-by: Sean Nyekjaer <sean@geanix.com>
>>>>>> ---
>>>>>> Documentation/devicetree/bindings/mfd/st,stpmic1.yaml | 8 =
++++++++
>>>>>> 1 file changed, 8 insertions(+)
>>>>>>=20
>>>>>> diff --git =
a/Documentation/devicetree/bindings/mfd/st,stpmic1.yaml =
b/Documentation/devicetree/bindings/mfd/st,stpmic1.yaml
>>>>>> index 9573e4af949e..5183a7c660d2 100644
>>>>>> --- a/Documentation/devicetree/bindings/mfd/st,stpmic1.yaml
>>>>>> +++ b/Documentation/devicetree/bindings/mfd/st,stpmic1.yaml
>>>>>> @@ -26,6 +26,14 @@ properties:
>>>>>>=20
>>>>>> interrupt-controller: true
>>>>>>=20
>>>>>> +  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).
>>>>>=20
>>>>> 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.
>>>>=20
>>>> Better wording?
>>>>     Indicates that the power management IC (PMIC) is used to power =
off the board.
>>>>     So as the last step in the power off sequence set the SWOFF bit =
in the
>>>>     main control register (MAIN_CR) register, to shutdown all power =
rails.
>>>=20
>>> 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.
>>>=20
>>> 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?
>>=20
>> 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.
>>=20
>> ?
>>=20
>> I must admit I=E2=80=99m somewhat lost here :)
>=20
> 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.")
>=20
> 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.
>=20

No silly questions, maybe they trick me to come up with the correct =
answer :D

Basically without this, you won=E2=80=99t be able to power off the =
system
other than hitting the PONKEY.
So it=E2=80=99s a new feature that wasn=E2=80=99t supported before.
Maybe this feature should not be optional?

If st,pmic-poweroff =3D=3D true:
System will power off as the last step in the power off sequence.
If st,pmic-powerof =3D=3D false:
System will reboot in the last step in the power off sequence.

I thought of this, as an always on system failsafe.

/Sean=