linux-kernel - Re: [PATCH 2/2] dt-bindings: rtc: add bindings for max313xx RTCs

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Message-ID: <c573ae8d-f2ee-403f-e096-eec4b31c682f@linaro.org>
Date:   Fri, 21 Oct 2022 09:40:30 -0400
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     "Tilki, Ibrahim" <Ibrahim.Tilki@...log.com>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>
Cc:     "a.zummo@...ertech.it" <a.zummo@...ertech.it>,
        "jdelvare@...e.com" <jdelvare@...e.com>,
        "linux@...ck-us.net" <linux@...ck-us.net>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "krzysztof.kozlowski+dt@...aro.org" 
        <krzysztof.kozlowski+dt@...aro.org>,
        "linux-rtc@...r.kernel.org" <linux-rtc@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-hwmon@...r.kernel.org" <linux-hwmon@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "Arslanbenzer, Zeynep" <Zeynep.Arslanbenzer@...log.com>
Subject: Re: [PATCH 2/2] dt-bindings: rtc: add bindings for max313xx RTCs

On 21/10/2022 09:05, Tilki, Ibrahim wrote:
>> On 21/10/2022 11:44:12+0000, Tilki, Ibrahim wrote:
>>>>> +  interrupt-names:
>>>>> +    description: |
>>>>> +      Name of the interrupt pin of the RTC used for IRQ. Not required for
>>>>> +      RTCs that only have single interrupt pin available. Some of the RTCs
>>>>> +      share interrupt pins with clock input/output pins.
>>>>> +    minItems: 1
>>>>> +    items:
>>>>> +      - enum: [INTA, INTB]
>>>>> +      - enum: [INTA, INTB]
>>>>> +
>>>>
>>>> I don't think this is right, what this is doing is essentially pinmuxing
>>>> interrupts versus clocks. What happens if you want INTB but this goes
>>>> directly to a PMIC instead of the SoC?
>>>> It is not something you can express with your current bindings.
>>>>
>>>
>>> Why would a user want INTB when it is not connected to SoC?
>>> User can specify none, either one or both of the interrupt pins.
>>> I don't see what the problem here is.
>>>
>>
>> the interrupt pin may be connected to a PMIC that is able to start or
>> wake up the platform. In that case, the user would not have any
>> interrupt-names and your driver will fail to mux the interrupt on INTB.
>> Please fix.
> 
> Interrupt muxing depends on the clock configuration, not the interrupt-names property.
> Devices don't support muxing the alarm interrupt independently.
> 
> For example in the case of max31329, alarm interrupt is muxed into INTA by default.
> Alarm interrupt is muxed into INTB pin if and only if clkin is enabled.\

Just to be sure: are you now describing hardware or Linux driver behavior?

> 
> This means that if a user wants the alarm interrupt on INTB pin, they have to
> provide a clock input through "clocks" property. If that is the case, they can provide
> an interrupt for INTB pin, otherwise the alarm feature of the rtc gets disabled.
> 
> Side note: Some devices have 2 Alarms but Alarm2 does not have a register for
> matching "seconds" so only Alarm1 is used by the driver.

Best regards,
Krzysztof