linux-kernel - Re: [PATCH 0/2] add ripple counter dt binding and driver

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Date:   Mon, 1 Mar 2021 10:44:48 +0100
From:   Arnd Bergmann <arnd@...nel.org>
To:     Rasmus Villemoes <linux@...musvillemoes.dk>
Cc:     Guenter Roeck <linux@...ck-us.net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Rob Herring <robh+dt@...nel.org>,
        DTML <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>,
        linux-clk <linux-clk@...r.kernel.org>,
        Wim Van Sebroeck <wim@...ux-watchdog.org>,
        "linux-watchdog@...r.kernel.org" <linux-watchdog@...r.kernel.org>
Subject: Re: [PATCH 0/2] add ripple counter dt binding and driver

On Mon, Mar 1, 2021 at 9:34 AM Rasmus Villemoes
<linux@...musvillemoes.dk> wrote:
> On 26/02/2021 20.53, Guenter Roeck wrote:
> >
> > Sorry, I am missing something. If the watchdog is controlled by the clock,
> > it is a consumer of that clock.
>
> But that's just it, the watchdog chip is _not_ a consumer of the clock -
> I don't think I've ever seen a gpio_wdt that is not internally clocked,
> but even if they exist, that's not the case for this board.
>
>  What else does "consumer" mean ? And why
> > not just add optional clock support to the gpio_wdt driver ?
>
> Because, the consumer is a piece of electronics sitting _between_ the
> watchdog chip's reset output and the SOCs reset pin, namely the ripple
> counter that implements a 64 ms delay from the watchdog fires till the
> actual reset. (The watchdog's reset is also routed directly to an
> interrupt; so software gets a 64 ms warning that a hard reset is imminent).

I think it's  a question of how you look at what the gpio_wdt device is.
While physical gpio chip is not a consumer of the clock, I agree with
Guenter that the conceptual device is: The functionality of the watchdog
in this case is provided by the combination of the external chip with the
ripple counter. I think it is therefore appropriate to have the gpio_wdt
and the driver refer to the clock as part of the watchdog.

        Arnd