linux-kernel - Re: [patch 0/2] semaphores: add down_interruptible

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Date:	Mon, 26 Feb 2007 16:54:17 -0800
From:	Inaky Perez-Gonzalez <inaky@...ux.intel.com>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Arjan van de Ven <arjan@...radead.org>, mingo@...hat.com,
	akpm@...l.org, linux-kernel@...r.kernel.org
Subject: Re: [patch 0/2] semaphores: add down_interruptible_timeout() and asm-generic/semaphore.h

On Monday 26 February 2007 16:33, Christoph Hellwig wrote:
> On Mon, Feb 26, 2007 at 04:13:38PM -0800, inaky@...ux.intel.com wrote:
> > Introduce down_interruptible_timeout() using timers to make the waiter
> > stop waiting by simulating a signal (see first patch for more
> > details). As well introduce asm-generic/semaphore.h and make other
> > architectures use it too.
>
> What do you want this for?  Do you really need a full counting semaphore
> or do you actually want a mutex?

Yeah, I need semaphore. This is a hw register that says when the hw
is ready to accept a new command. Code that wants to send commands has
to down the semaphore and then send it. When hw is ready to get a new
command, it sends and IRQ and the IRQ up()s the semaphore. 

Now, we don't want to hang on that down() forever if the hw spaces out.
If we get a timeout, we can try recovery actions (like resetting it,
for sake of being polite). 

I use this in the WHCI Ultra Wide Band radio controller code (coming soon
to a hw store near you).

Cristoph, I still wonder how the hell you do it to spot every message
that comes into lkml -- I bet you have a cluster of employees using your
name doing it... :)

-- Inaky
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