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

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Message-ID: <CAL_Jsq+HeeFUR1Yv37X4OnkEPvSiAc2B86=Nshxz7tmvpKk+zw@mail.gmail.com>
Date:   Thu, 17 Dec 2020 10:51:08 -0600
From:   Rob Herring <robh+dt@...nel.org>
To:     Rasmus Villemoes <rasmus.villemoes@...vas.dk>
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 Fri, Dec 11, 2020 at 5:10 PM Rasmus Villemoes
<rasmus.villemoes@...vas.dk> wrote:
>
> 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?

Yeah, I guess you're right.

> 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).

I'm wondering how you solve which wdog to ping when there are multiple
without relying on numbering. I guess 'reset-source' will solve that
even if that's not your current fix. So I guess I'm fine with this.

But you need to send to the DT list so checks are run.

Rob