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Subject: Re: [PATCH v1 1/4] dt-binding: watchdog: add restart priority
 documentation
To:     Tomer Maimon <tmaimon77@gmail.com>
Cc:     Wim Van Sebroeck <wim@linux-watchdog.org>,
        Rob Herring <robh+dt@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Joel Stanley <joel@jms.id.au>,
        Avi Fishman <avifishman70@gmail.com>,
        Tali Perry <tali.perry1@gmail.com>,
        Nancy Yuen <yuenn@google.com>,
        Benjamin Fair <benjaminfair@google.com>,
        linux-watchdog@vger.kernel.org,
        devicetree <devicetree@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        OpenBMC Maillist <openbmc@lists.ozlabs.org>
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From:   Guenter Roeck <linux@roeck-us.net>
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Message-ID: <e009d5e5-03a1-301c-0a65-c7f59c1be9fa@roeck-us.net>
Date:   Sun, 1 Mar 2020 07:46:44 -0800
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On 3/1/20 7:36 AM, Tomer Maimon wrote:
> 
> 
> On Sun, 1 Mar 2020 at 12:06, Guenter Roeck <linux@roeck-us.net <mailto:linux@roeck-us.net>> wrote:
> 
>     On 3/1/20 1:40 AM, Tomer Maimon wrote:
>     > Add device tree restart priority documentation.
>     >
> 
>     I think this warrants an explanation _why_ this is needed.
>     What is the use case ? Not just theory, please.
> 
> 
> In the NPCM750 there is two initiated restarts:
> 
>   * Software reset
>   * WD reset
> 
> the Software restart found at NPCM reset driver
> https://github.com/torvalds/linux/blob/master/drivers/reset/reset-npcm.c
> 
> In NPCM WD driver the restart is configure as well, I will like to add the priority so the user will have maximum flexibility if he using both restarts
> 

This is not the intended use case for restart priority. It is not
intended to be user configurable. The idea is that the more thorough
restart gets higher priority. This is implied by the restart method,
not by user preferences.

Also, the idea behind supporting multiple means to reset the system
is to be able to support multiple means to restart, some of which
may not always be available. In that situation, the priority means,
and is supposed to mean, "pick the best restart method available".
Again, that is determined by system design, and not supposed to
be configurable by the user.

On top of that, a watchdog driver based reset is almost always
a reset of last resort, to be chosen only if nothing else is available
in a given system. The existence of the reset driver confirms that
this is not different for this driver/chip.

Guenter