On Tue, Aug 21, 2007 at 01:02:01AM +0200, Segher Boessenkool wrote:

quoted

quoted

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: