linux-kernel - Re: [PATCH v5 2/2] dt-bindings: rtc: add max313xx RTCs

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Message-ID: <2023040407444619bf5596@mail.local>
Date:   Tue, 4 Apr 2023 09:44:46 +0200
From:   Alexandre Belloni <alexandre.belloni@...tlin.com>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
Cc:     Ibrahim Tilki <Ibrahim.Tilki@...log.com>, a.zummo@...ertech.it,
        jdelvare@...e.com, linux@...ck-us.net, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.org, linux-rtc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-hwmon@...r.kernel.org,
        devicetree@...r.kernel.org,
        Zeynep Arslanbenzer <Zeynep.Arslanbenzer@...log.com>
Subject: Re: [PATCH v5 2/2] dt-bindings: rtc: add max313xx RTCs

On 04/04/2023 09:21:56+0200, Krzysztof Kozlowski wrote:
> On 04/04/2023 09:10, Alexandre Belloni wrote:
> >>
> >>> +      RTC can be used as a clock source through its clock output pin when
> >>> +      supplied.
> >>> +    const: 0
> >>> +
> >>> +  clocks:
> >>> +    description: |
> >>
> >> Do not need '|'.
> >>
> >>> +      RTC uses this clock for clock input when supplied. Clock has to provide
> >>> +      one of these four frequencies: 1Hz, 50Hz, 60Hz or 32.768kHz.
> >>> +    maxItems: 1
> >>> +
> >>> +  aux-voltage-chargeable:
> >>> +    enum: [0, 1, 2]
> >>> +    description: |
> >>> +      Enables trickle charger.
> >>> +      0: Charger is disabled (default)
> >>> +      1: Charger is enabled
> >>> +      2: Charger is enabled with a diode
> >>
> >> 2 is not an allowed value. I asked to drop this property. It is coming
> >> from rtc.yaml. I also do not understand "with a diode". So otherwise it
> >> is charging with, I don't know, FET?
> > 
> > No, what is not explained here (and maybe not unsterstood by the
> > submitter) is that the RTC has an extra diode so, 
> 
> Value of 2 is still not allowed and if the patch was tested, it would be
> clearly visible. Unfortunately patch was not tested...
> 
> > charging will always
> > enable a diode, select a resistor and then have or not an extra diode.
> > Figure2 of the MAX31329 datasheet is great.
> 
> So the diode is in the max313xx? Then why enabling it is a property of
> DT? Either this should be inferred from compatible or is even a policy,
> not a DT property. Just because device has a register for something, is
> not an argument that "something" should be in DT.

Well, it depends on the battery that is installed on the board so it
makes sense to have it in DT.

-- 
Alexandre Belloni, co-owner and COO, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com