linux-kernel - Re: drivers/watchdog/geodewdt.c: build fix

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Message-ID: <20080530162442.GB16164@csclub.uwaterloo.ca>
Date:	Fri, 30 May 2008 12:24:42 -0400
From:	lsorense@...lub.uwaterloo.ca (Lennart Sorensen)
To:	Jordan Crouse <jordan.crouse@....com>
Cc:	David Brigada <brigad@....edu>, Ingo Molnar <mingo@...e.hu>,
	Wim Van Sebroeck <wim@...ana.be>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Samuel Tardieu <sam@...1149.net>,
	Mike Frysinger <vapier.adi@...il.com>,
	Mingarelli@...omag.amd.com
Subject: Re: drivers/watchdog/geodewdt.c: build fix

On Fri, May 30, 2008 at 10:05:05AM -0600, Jordan Crouse wrote:
> I think the hamster dropping code is queued for 2.6.27, so at least we're
> up to mammals.
> 
> The story here is that in an unfortunate instance of bad planning the
> MFGPT timers can only be configured once, so a module can't allocate a
> timer at init and release it when it is done.  The original object of this
> code was to try give the timer back to a module if it happened to go away
> and come back, but that is clearly a more complex process then just simply
> storing the module name, and this code fell into bitrot.

It is a bit unfortunate that someone decided to design 'configure once'
hardware.  What were they thinking?

I run a watchdog using the mfgpt, and I simply tore out the code that
prevents reuse of the timers, and I decided which timers I am going to
use for which purpose and never reuse them for anything else, so the
parts of the configuration in the hardware that is fixed isn't an issue
then.  I start the watchdog from grub, so I had to override the check
when the kernel takes over the timer watchdog management after all.

> So its not so much that we need to drop module support, rather it needs to
> be understood that if you remove and insert your module on a regular basis
> you will run out of timers, and deprive others of the timers too. I think
> that is a reasonable restriction to impose, given the limited usefulness 
> of these timers for general purpose use.

They are useful timers, but yes perhaps not for general purpose.  As a
source of interrupts at certain intervals or as a watchdog they are not
too bad.

-- 
Len Sorensen
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