From: Inaky Perez-Gonzalez <inaky@linux.intel.com>
Organization: Intel Corporation
To: Alan <alan@lxorguk.ukuu.org.uk>
Subject: Re: [patch 0/2] semaphores: add down_interruptible_timeout() and asm-generic/semaphore.h
Date: Mon, 26 Feb 2007 17:57:11 -0800
User-Agent: KMail/1.9.5
Cc: Christoph Hellwig <hch@infradead.org>,
       Arjan van de Ven <arjan@infradead.org>, mingo@redhat.com, akpm@osdl.org,
       linux-kernel@vger.kernel.org
References: <20070227001338.344233745@sodium.jf.intel.com> <200702261654.18005.inaky@linux.intel.com> <20070227021803.38c8591f@lxorguk.ukuu.org.uk>
In-Reply-To: <20070227021803.38c8591f@lxorguk.ukuu.org.uk>
MIME-Version: 1.0
Content-Type: text/plain;
  charset="iso-8859-1"
Content-Transfer-Encoding: 7bit
Content-Disposition: inline
Message-Id: <200702261757.11968.inaky@linux.intel.com>
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1023
Lines: 21

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...
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/