linux-kernel - Re: [PATCH v2 1/6] wdt: sunxi: Move restart code to the watchdog driver

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Message-ID: <20298828.cYNPnTRxWX@wuerfel>
Date:	Tue, 24 Jun 2014 11:27:45 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	linux-arm-kernel@...ts.infradead.org
Cc:	Guenter Roeck <linux@...ck-us.net>,
	Wim Van Sebroeck <wim@...ana.be>,
	Maxime Ripard <maxime.ripard@...e-electrons.com>,
	linux-watchdog@...r.kernel.org, dbaryshkov@...il.com,
	linux-kernel@...r.kernel.org, linux-sunxi@...glegroups.com,
	dwmw2@...radead.org
Subject: Re: [PATCH v2 1/6] wdt: sunxi: Move restart code to the watchdog driver

On Monday 23 June 2014 14:47:48 Guenter Roeck wrote:
> > To continue the discussion: I would like to add an excerpt from drivers/watchdog/alim7101_wdt.c
> > /*
> >   *      Notifier for system down
> >   */
> >
> > static int wdt_notify_sys(struct notifier_block *this,
> >                                          unsigned long code, void *unused)
> > {
> >          if (code == SYS_DOWN || code == SYS_HALT)
> >                  wdt_turnoff();
> >
> >          if (code == SYS_RESTART) {
> >                  /*
> >                   * Cobalt devices have no way of rebooting themselves other
> >                   * than getting the watchdog to pull reset, so we restart the
> >                   * watchdog on reboot with no heartbeat
> >                   */
> >                  wdt_change(WDT_ENABLE);
> >                  pr_info("Watchdog timer is now enabled with no heartbeat - should reboot in ~1 second\n");
> >          }
> >          return NOTIFY_DONE;
> > }
> >
> > For some systems the watchdog is the only way to reboot... So where we should put it, is not trivial neither...
> >
> 
> Agreed. The above definitely doesn't look like a good solution to me.
> 

Right, at the very least, it should be a separate notifier: the existing
reboot_notifier is meant for things that need to happen /before/ reboot,
so adding something in there to actually trigger the reboot is by definition
racy against the other notifiers that may or may not get called after
this one.

	Arnd
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