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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: <b9297205-82fa-8cdf-550e-a53c073e0a9d@linaro.org>
Date:   Thu, 1 Jun 2023 16:05:17 +0200
Cc:     Conor Dooley <conor.dooley@microchip.com>,
        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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 <20230524-ellipse-dagger-72f850253ea0@wendy>
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 <b9297205-82fa-8cdf-550e-a53c073e0a9d@linaro.org>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Precedence: bulk

Hi Krzysztof,

> On 1 Jun 2023, at 09.12, Krzysztof Kozlowski =
<krzysztof.kozlowski@linaro.org> wrote:
>=20
> On 24/05/2023 12:30, Sean Nyekjaer wrote:
>>=20
>>=20
>>> 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
>>=20
>> No silly questions, maybe they trick me to come up with the correct =
answer :D
>>=20
>> 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?
>=20
> You are still describing what driver should do with registers. What =
you
> are missing is describing real cause for this. It's exactly the same
> case as was with s2mps11.

I didn=E2=80=99t mention anything with registers in the patch:

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).

^^ That=E2=80=99s is exactly what is happening if the option is enabled.

Do you have a suggestion wording?
What do you think about removing this option and make it default =
behaviour?

/Sean

>=20
> Best regards,
> Krzysztof
>=20