linux-kernel - Re: [PATCH] dt-bindings: rtc: pcf2127: update bindings

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Message-ID: <20210127131821.GH1196852@piout.net>
Date:   Wed, 27 Jan 2021 14:18:21 +0100
From:   Alexandre Belloni <alexandre.belloni@...tlin.com>
To:     Rasmus Villemoes <rasmus.villemoes@...vas.dk>
Cc:     Alessandro Zummo <a.zummo@...ertech.it>,
        Rob Herring <robh+dt@...nel.org>, linux-rtc@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] dt-bindings: rtc: pcf2127: update bindings

On 27/01/2021 14:07:59+0100, Rasmus Villemoes wrote:
> On 26/01/2021 23.48, Alexandre Belloni wrote:
> > On 21/12/2020 22:17:54+0100, Rasmus Villemoes wrote:
> >> On 19/12/2020 02.34, Alexandre Belloni wrote:
> >>> pcf2127, pcf2129 and pca2129 support start-year and reset-source.
> >>>
> >>
> >> No, the 2129 variant doesn't even have a reset output pin. Not sure if
> >> there's any way to reflect that, and it probably doesn't matter, since
> >> nobody's going to add the reset-source property to a 2129 node. But the
> >> commit message is a bit misleading.
> >>
> > 
> > Actually no, the INT pin can be used as a reset, the pcf/pca2129
> > can be used as a watchdog and so it may need the reset-source property.
> 
> Unless I'm missing something, that would require some rather creative
> extra circuitry: The interrupt pin is kept low until the appropriate bit
> in the rtc is cleared, so if that is routed directly to a reset pin on
> the SOC, the SOC would be kept in reset indefinitely.
> 

You mean inverting the level of INT? I don't think this is creative or
complicated...
And anyway, INT# is active low, like RST# so if the SoC has an RST#
input, this should just work.

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