linux-kernel - Re: [PATCH 1/10 v2] Generic Watchdog Timer Driver

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Date:	Fri, 24 Jun 2011 21:27:42 +0200
From:	Wim Van Sebroeck <wim@...ana.be>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Linux Watchdog Mailing List <linux-watchdog@...r.kernel.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>
Subject: Re: [PATCH 1/10 v2] Generic Watchdog Timer Driver

Hi Arnd,

> > > > +#include <linux/platform_device.h>
> > > > +
> > > > +/* Hardware heartbeat in seconds */
> > > > +#define WDT_HW_HEARTBEAT 2
> > > > +
> > > > +/* Timer heartbeat (500ms) */
> > > > +#define WDT_HEARTBEAT	(HZ/2)	/* should be <= ((WDT_HW_HEARTBEAT*HZ)/2) */
> > > > +
> > > > +/* User land timeout */
> > > > +#define WDT_TIMEOUT 15
> > > > +static int timeout = WDT_TIMEOUT;
> > > > +module_param(timeout, int, 0);
> > > > +MODULE_PARM_DESC(timeout, "Watchdog timeout in seconds. "
> > > > +	"(default = " __MODULE_STRING(WDT_TIMEOUT) ")");
> > > 
> > > Should the module parameter really be part of each individual driver?
> > > It would be nice if that can be moved into the core as well.
> > 
> > Yes, the module parameter is needed for each individual driver.
> > If we go for supporting multiple watchdog devices, then we will have to support
> > different timeout values. The timeout ranges also differ for different devices.
> 
> Ok, but you'd still have to worry about a single driver supporting multiple
> distinct devices that each want a separate timeout, right?

If it's a single driver that supports different devices (say an SuperIO controller
with several watchdog timers and different GPIO output's), then I still presume that
the timeout range for these different devices will be the same. But I can indeed
imagine that these timers will be used for monitoring different "processes" that
will have different latency and timeout values.

> OTOH, we can still find a solution when it ever gets to the point of
> supporting multiple devices.

Yep, if we support different watchdog devices, then we will need something
to change the default value anyway (like the ioctl does now for a single instance).

Kind regards,
Wim.

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