linux-kernel - Re: [PATCH] RFC, watchdog: add generic wdt driver API

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Date:	Sun, 04 Dec 2011 18:08:10 +0100
From:	Wolfgang Denk <wd@...x.de>
To:	Wolfram Sang <w.sang@...gutronix.de>
cc:	Heiko Schocher <hs@...x.de>, linux-watchdog@...r.kernel.org,
	devicetree-discuss@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
	Stefan Roese <sr@...x.de>
Subject: Re: [PATCH] RFC, watchdog: add generic wdt driver API

Dear Wolfram,

In message <20111204125928.GB5788@...gutronix.de> you wrote:
> 
> > This patch is a port from Linux 2.4 and thought as an RFC, so comments
> > are greately appreciated. First question is, has this watchdog driver
> > API a chance to go in mainline? If so, what is the direction to
> > go to push it ...
> 
> I don't see this flying. We finally have a watchdog framework in the kernel
> which covers the long existing API used by existing drivers. If I understood it
> right, this additional API needs new drivers for all the watchdogs? Also, I
> didn't fully get what you are missing from the combination of the current API
> and additional userspace-handling? (check [1] for one example, not really

Watchdog support is somethign that usually comes into play for
security-critical devices.  Doing this stuff in user space may or may
not be sufficient; for example, we've seen requirements where all
related code must be running from ROM (including all other kernel
code).

Also, the implementation submitted by Heiko allows for easy watchdog
control for kernel tasks.  I don;t see a good way to do this through
user space.

But as Heikow wrote; this is a RFC patch, and the main purpose is to
try to find out if it has a chance to go into mainline - several
earlier attempts (which go back as far as 2002 - see for example [1],
[2]) all failed with similar arguments like yours: "It's too complex,
we already have watchdog support, nobody needs this". Funny enough
that we have a number of customers who consider the existing wdt
support unsufficient for their use cases.  We've been using it on all
kinds on PPC systems, and now on ARM as well.

We will not fight for inclusion of this driver, we just wat to know if
it's worth investing efforts to get it accepted or if this is a lost
case.

[1] http://osdir.com/ml/linux.ports.ppc.embedded/2003-12/msg00188.html
[2] http://thread.gmane.org/gmane.linux.kernel/884598

Best regards,

Wolfgang Denk

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