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

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Message-Id: <200702261757.11968.inaky@linux.intel.com>
Date:	Mon, 26 Feb 2007 17:57:11 -0800
From:	Inaky Perez-Gonzalez <inaky@...ux.intel.com>
To:	Alan <alan@...rguk.ukuu.org.uk>
Cc:	Christoph Hellwig <hch@...radead.org>,
	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 18:18, Alan wrote:
> > 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.
>
> So you need a mutex not a semaphore

Theoretically I could use a mutex. Practically it would trigger ugly
complications. Only the owner can unlock a mutex (for example), so
I could not unlock from an IRQ handler -- not to mention that the
semantic rules outlined in Documentation/mutex-design.txt explicitly
forbid IRQ usage. 

And then, this is what semaphores where designed for, as gates :)
for once that I get to use a semaphore properly...
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