linux-kernel - Re: [PATCH 2/6] dt-bindings: rtc: stm32: add alarm A out property to select output

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Date:   Mon, 23 May 2022 14:34:22 +0200
From:   Valentin CARON <valentin.caron@...s.st.com>
To:     Alexandre Belloni <alexandre.belloni@...tlin.com>
CC:     Alessandro Zummo <a.zummo@...ertech.it>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Alexandre Torgue <alexandre.torgue@...s.st.com>,
        Gabriel Fernandez <gabriel.fernandez@...s.st.com>,
        Amelie Delaunay <amelie.delaunay@...s.st.com>,
        <linux-rtc@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-stm32@...md-mailman.stormreply.com>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/6] dt-bindings: rtc: stm32: add alarm A out property to
 select output

Hi Alexandre,

On 5/4/22 22:27, Alexandre Belloni wrote:
> Hello,
>
> On 04/05/2022 15:06:13+0200, Valentin Caron wrote:
>> STM32 RTC can pulse some SOC pins when an alarm of RTC expires.
>>
>> This patch adds property to activate alarm A output. The pulse can
>> output on three pins RTC_OUT1, RTC_OUT2, RTC_OUT2_RMP
>> (PC13, PB2, PI8 on stm32mp15) (PC13, PB2, PI1 on stm32mp13).
>>
>> Signed-off-by: Valentin Caron <valentin.caron@...s.st.com>
>> ---
>>   .../devicetree/bindings/rtc/st,stm32-rtc.yaml | 19 ++++++++++++++++++-
>>   1 file changed, 18 insertions(+), 1 deletion(-)
>>
>> diff --git a/Documentation/devicetree/bindings/rtc/st,stm32-rtc.yaml b/Documentation/devicetree/bindings/rtc/st,stm32-rtc.yaml
>> index 56d46ea35c5d..71e02604e8de 100644
>> --- a/Documentation/devicetree/bindings/rtc/st,stm32-rtc.yaml
>> +++ b/Documentation/devicetree/bindings/rtc/st,stm32-rtc.yaml
>> @@ -59,6 +59,13 @@ properties:
>>         Refer to <include/dt-bindings/rtc/rtc-stm32.h> for the supported values.
>>         Pinctrl state named "default" may be defined to reserve pin for RTC output.
>>   
>> +  st,alarm:
>> +    $ref: "/schemas/types.yaml#/definitions/uint32"
>> +    description: |
>> +      To select and enable RTC Alarm A output.
>> +      Refer to <include/dt-bindings/rtc/rtc-stm32.h> for the supported values.
>> +      Pinctrl state named "default" may be defined to reserve pin for RTC output.
>> +
>>   allOf:
>>     - if:
>>         properties:
>> @@ -75,6 +82,9 @@ allOf:
>>           st,lsco:
>>             maxItems: 0
>>   
>> +        st,alarm:
>> +          maxItems: 0
>> +
>>           clock-names: false
>>   
>>         required:
>> @@ -95,6 +105,9 @@ allOf:
>>           st,lsco:
>>             maxItems: 0
>>   
>> +        st,alarm:
>> +          maxItems: 0
>> +
>>         required:
>>           - clock-names
>>           - st,syscfg
>> @@ -117,6 +130,9 @@ allOf:
>>           st,lsco:
>>             maxItems: 1
>>   
>> +        st,alarm:
>> +          maxItems: 1
>> +
>>         required:
>>           - clock-names
>>   
>> @@ -153,8 +169,9 @@ examples:
>>         clocks = <&rcc RTCAPB>, <&rcc RTC>;
>>         clock-names = "pclk", "rtc_ck";
>>         interrupts = <GIC_SPI 3 IRQ_TYPE_LEVEL_HIGH>;
>> +      st,alarm = <RTC_OUT1>;
>>         st,lsco = <RTC_OUT2_RMP>;
> Shouldn't that be exactly the opposite? You have two pins that can
> output different functions. The property should be the pin and the value
> the function. I'd go even further and I would say this is actually
> pinmuxing.
>
You're right, if the property is the pin and the value the function, 
this looks like a pinctrl node.
We choose to develop theses functionalities in the reverse order, to 
avoid the complexity of adding
the pinctrl framework to our driver. Moreover, LSCO and AlarmA may 
haven't a peripheral client and
this would probably require to also implement pinctrl hogging.

Is the implementation that we have proposed is acceptable regarding 
theses elements ?

Thank you,
Valentin