netdev - Re: [PATCH 0/24] make atomic_read() behave consistently across all architectures

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Message-ID: <20070821070555.GA32036@flint.arm.linux.org.uk>
Date:	Tue, 21 Aug 2007 08:05:55 +0100
From:	Russell King <rmk+lkml@....linux.org.uk>
To:	Segher Boessenkool <segher@...nel.crashing.org>
Cc:	Christoph Lameter <clameter@....com>,
	Paul Mackerras <paulus@...ba.org>, heiko.carstens@...ibm.com,
	horms@...ge.net.au, linux-kernel@...r.kernel.org,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>, ak@...e.de,
	netdev@...r.kernel.org, cfriesen@...tel.com,
	akpm@...ux-foundation.org, rpjday@...dspring.com,
	Nick Piggin <nickpiggin@...oo.com.au>,
	linux-arch@...r.kernel.org, jesper.juhl@...il.com,
	satyam@...radead.org, zlynx@....org, schwidefsky@...ibm.com,
	Chris Snook <csnook@...hat.com>,
	Herbert Xu <herbert@...dor.apana.org.au>, davem@...emloft.net,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	wensong@...ux-vs.org, wjiang@...ilience.com
Subject: Re: [PATCH 0/24] make atomic_read() behave consistently across all architectures

On Tue, Aug 21, 2007 at 01:02:01AM +0200, Segher Boessenkool wrote:
> >>And no, RMW on MMIO isn't "problematic" at all, either.
> >>
> >>An RMW op is a read op, a modify op, and a write op, all rolled
> >>into one opcode.  But three actual operations.
> >
> >Maybe for some CPUs, but not all.  ARM for instance can't use the
> >load exclusive and store exclusive instructions to MMIO space.
> 
> Sure, your CPU doesn't have RMW instructions -- how to emulate
> those if you don't have them is a totally different thing.

Let me say it more clearly: On ARM, it is impossible to perform atomic
operations on MMIO space.

-- 
Russell King
 Linux kernel    2.6 ARM Linux   - http://www.arm.linux.org.uk/
 maintainer of:
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