From mboxrd@z Thu Jan  1 00:00:00 1970
From: Jamie Lokier <jamie@shareable.org>
Subject: Re: [ACPI] Re: Linux 2.4.26-rc1 (cmpxchg vs 80386 build)
Date: Wed, 31 Mar 2004 16:02:19 +0100
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To: "Maciej W. Rozycki" <macro@ds2.pg.gda.pl>
Cc: Bill Davidsen <davidsen@tmr.com>, Len Brown <len.brown@intel.com>, Chris Friesen <cfriesen@nortelnetworks.com>, Willy Tarreau <willy@w.ods.org>, "Richard B. Johnson" <root@chaos.analogic.com>, Alan Cox <alan@lxorguk.ukuu.org.uk>, Arkadiusz Miskiewicz <arekm@pld-linux.org>, Marcelo Tosatti <marcelo.tosatti@cyclades.com>, Linux Kernel Mailing List <linux-kernel@vger.kernel.org>, ACPI Developers <acpi-devel@lists.sourceforge.net>
List-Id: linux-acpi@vger.kernel.org

Maciej W. Rozycki wrote:
>  Well, "cmpxchg", "xadd", etc. can be easily emulated with an aid of a
> spinlock.  With SMP operation included.

Nope.  Len Brown wrote:

> Linux uses this locking mechanism to coordinate shared access
> to hardware registers with embedded controllers,
> which is true also on uniprocessors too.

You can't do that with a spinlock.  The embedded controllers would
need to know about the spinlock.

-- Jamie