[patch] powerpc: implement optimised mutex fastpaths

[Scott Wood]

On Sun, Oct 12, 2008 at 07:47:32AM +0200, Nick Piggin wrote:
> +static inline int __mutex_cmpxchg_lock(atomic_t *v, int old, int new)
> +{
> +	int t;
> +
> +	__asm__ __volatile__ (
> +"1:	lwarx	%0,0,%1		# mutex trylock\n\
> +	cmpw	0,%0,%2\n\
> +	bne-	2f\n"
> +	PPC405_ERR77(0,%1)
> +"	stwcx.	%3,0,%1\n\
> +	bne-	1b"
> +	ISYNC_ON_SMP
> +	"\n\
> +2:"
> +	: "=&r" (t)
> +	: "r" (&v->counter), "r" (old), "r" (new)
> +	: "cc", "memory");

This will break if the compiler picks r0 for &v->counter.  Use "b" as the
constraint, or better yet do "lwarx %0, %y1", with a "Z" (v->counter)
constraint.

-Scott