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

From: Russell King <[email-masked]>
Date: Tue, 21 Aug 2007 08:05:55 +0100

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: