linux-kernel - Re: watchdog start on restart

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Message-ID: <7a58bc3f80783170ecc38371aad7addc04397787.camel@yadro.com>
Date:   Thu, 3 Sep 2020 16:26:18 +0300
From:   Ivan Mikhaylov <i.mikhaylov@...ro.com>
To:     Christophe Leroy <christophe.leroy@...roup.eu>,
        Guenter Roeck <linux@...ck-us.net>
CC:     Wim Van Sebroeck <wim@...ux-watchdog.org>,
        <linux-watchdog@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: watchdog start on restart

On Thu, 2020-09-03 at 13:13 +0200, Christophe Leroy wrote:

> You want to start the watchdog just before calling 'reboot' but want to 
> make sure that the watchdog will not reset the board before all 
> userspace has shut down correctly ?

Yes, just for an example, in the nature exists some aspeed2400/2500 board which
has 2 watchdog devices and 2 spi flash memories. By default it starts from 1 spi
flash. When watchdog triggers, on next boot, it's automatically starts from 2
flash, also you can manually switch from 1 spi flash to 2 with 2 watchdog device
by trigger of it, like transparent reload from 1 spi flash side to 2.

> But what is the purpose of the watchdog then, isn't it there to make 
> sure that the machine gets reboot within a given timeout anyway in case 
> some userspace takes too long to shut down ?

Usually, yes.

Thanks.