linux-kernel - Re: [PATCH v2 1/3] dt-bindings: rtc: add reset-source property

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Date:   Sat, 12 Dec 2020 00:10:11 +0100
From:   Rasmus Villemoes <rasmus.villemoes@...vas.dk>
To:     Rob Herring <robh+dt@...nel.org>
Cc:     "open list:REAL TIME CLOCK (RTC) SUBSYSTEM" 
        <linux-rtc@...r.kernel.org>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Uwe Kleine-König <u.kleine-koenig@...gutronix.de>,
        Qiang Zhao <qiang.zhao@....com>,
        Bruno Thomsen <bruno.thomsen@...il.com>
Subject: Re: [PATCH v2 1/3] dt-bindings: rtc: add reset-source property

On 11/12/2020 23.30, Rob Herring wrote:
> On Fri, Dec 11, 2020 at 3:56 PM Rasmus Villemoes
> <rasmus.villemoes@...vas.dk> wrote:
>>
>> Some RTCs, e.g. the pcf2127, can be used as a hardware watchdog. But
>> if the reset pin is not actually wired up, the driver exposes a
>> watchdog device that doesn't actually work.
>>
>> Provide a standard binding that can be used to indicate that a given
>> RTC can perform a reset of the machine, similar to wakeup-source.
> 
> Why not use the watchdog 'timeout-sec' property?

Wouldn't that be overloading that property? AFAIU, that is used to ask
the kernel to program an initial timeout value into the watchdog device.
But what if one doesn't want to start the watchdog device at kernel
boot, but just indicate that the RTC has that capability?

It's quite possible that if it can act as a watchdog device (and
has-watchdog was also suggested), one would also want timeout-sec and
other watchdog bindings to apply. But that can be added later, by those
who actually want that.

For now, I'd really like to get my board booting again (or rather, not
get reset by the real watchdog just because the pcf2127 driver now
exposes something as /dev/wathdog0, pushing the real one to
/dev/wathcdog1 which doesn't get pinged from userspace).

Rasmus