[PATCH] Document Linux's memory barriers [try #4]

Michael Buesch mbuesch at freenet.de
Fri Mar 10 10:45:09 EST 2006

On Friday 10 March 2006 00:34, you wrote:
> David Howells writes:
> > +On some systems, I/O writes are not strongly ordered across all CPUs, and so
> > +locking should be used, and mmiowb() should be issued prior to unlocking the
> > +critical section.
> I think we should say more strongly that mmiowb() is required where
> MMIO accesses are done under a spinlock, and that if your driver is
> missing them then that is a bug.  I don't think it makes sense to say
> that mmiowb is required "on some systems".

So what about:

#define spin_lock_mmio(lock)	spin_lock(lock)
#define spin_unlock_mmio(lock)	do { spin_unlock(lock); mmiowb(); } while (0)
#define spin_lock_mmio_irqsave(lock, flags)	spin_lock_irqsave(lock, flags)
#define spin_unlock_mmio_irqrestore(lock, flags)	do { spin_unlock_irqrestore(lock, flags); mmiowb(); } while (0)

Greetings Michael.
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