linux-kernel - Re: [PATCH 2/2] dt-bindings: rtc: nxp,pcf8563: add hiz-output property

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Date:   Thu, 26 Oct 2023 01:23:21 +0200
From:   Javier Carrasco <javier.carrasco@...fvision.net>
To:     Alexandre Belloni <alexandre.belloni@...tlin.com>
Cc:     Alessandro Zummo <a.zummo@...ertech.it>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>, linux-rtc@...r.kernel.org,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org
Subject: Re: [PATCH 2/2] dt-bindings: rtc: nxp,pcf8563: add hiz-output
 property

Hi,

On 26.10.23 00:30, Javier Carrasco wrote:
> Hi Alexandre,
> 
> On 26.10.23 00:23, Alexandre Belloni wrote:
>> Hello,
>>
>> I'm sorry I never replied to your previous thread...
>>
>> On 25/10/2023 18:21:55+0200, Javier Carrasco wrote:
>>> The "hiz-output" property models the RTC output as a high-impedance
>>> (hi-Z) output.
>>>
>>> This property is optional and if it is not defined, the output will
>>> either act as an output clock (default mode) or as an interrupt
>>> depending on the configuration set by other properties.
>>>
>>> Two modes are defined in case the high-impedance is used: "enabled" and
>>> "sleep". The former disables the RTC output completely while the latter
>>> keeps the RTC output disabled until the system enters in sleep mode.
>>> This option is especially relevant if the output clock is used to feed a
>>> PMU, a PMIC or any other device required to run when the rest of the
>>> system is down. For the sake of completeness, a "disabled" mode has been
>>> added, which acts as if the property was not defined.
>>>
>>> Document "hiz-output" as a non-required property.
>>>
>>> Signed-off-by: Javier Carrasco <javier.carrasco@...fvision.net>
>>> ---
>>>  Documentation/devicetree/bindings/rtc/nxp,pcf85363.yaml | 14 ++++++++++++++
>>>  1 file changed, 14 insertions(+)
>>>
>>> diff --git a/Documentation/devicetree/bindings/rtc/nxp,pcf85363.yaml b/Documentation/devicetree/bindings/rtc/nxp,pcf85363.yaml
>>> index 52aa3e2091e9..4b27a9154191 100644
>>> --- a/Documentation/devicetree/bindings/rtc/nxp,pcf85363.yaml
>>> +++ b/Documentation/devicetree/bindings/rtc/nxp,pcf85363.yaml
>>> @@ -36,6 +36,19 @@ properties:
>>>      enum: [6000, 7000, 12500]
>>>      default: 7000
>>>  
>>> +  hiz-output:
>>> +    description:
>>> +      Use enabled if the output should stay in high-impedance. This
>>> +      mode will mask the output as an interrupt source.
>>> +      Use sleep if the otuput should be only active in sleep mode.
>>> +      This mode is compatible with any other output configuration.
>>> +      The disabled value acts as if the property was not defined.
>>> +    enum:
>>> +      - enabled
>>> +      - sleep
>>> +      - disabled
>>> +    default: disabled
>>> +
>>
>> If instead of using a custom property, you consider this as what it
>> actually is: pinmuxing, then everything else comes for free. With
>> pinctrl, you can define different states for runtime and sleep and they
>> will get applied automatically instead of open coding in the driver.

I am not sure if your solution would cover all my needs:

1.- With pinctrl I can model the SoC pins, right? That would not stop
the RTC output though, so the 32 kHz signal would be generated anyways
even though the SoC would ignore it. That is one of the things I want to
avoid.

2.- What happens if the RTC output is a clock for an external device
that is only required when the SoC is in sleep mode? In that case I
would like the RTC driver to control the output with the modes it provides.
>>
>> Also, how you define this property means that everyone currently using
>> this RTC is going to have a new warning that they should just ignore.
>>
>>
> Thanks for your reply. The warning can only be triggered if the property
> is defined, so in principle no one could have that warning yet. Only the
> ones who actually define it and use an invalid value would get the warning.
> 
> On the other hand I did not consider your approach, which might make
> this patch irrelevant. So I will have a look at it to make sure that it
> achieves the same results.
> 
> Thanks again and best regards,
> Javier Carrasco
>