Re: [PATCH 1/5] atomic: introduce atomic_cmpxchg

[Russell King <rmk+lkml@arm.linux.org.uk>]

On Thu, Sep 15, 2005 at 12:48:05AM +1000, Nick Piggin wrote:
> This patch still needs work on arm (v6) and m32r. I would
> just be shooting in the dark if I attempted either myself.

ARMv6, something like:

int atomic_cmpxchg(atomic_t *ptr, int old, int new)
{
	u32 oldval, res;

	do {
		asm(
		"ldrex	%1, [%2]\n\t"
		"teq	%1, %3\n\t"
		"strexeq %0, %4, [%2]\n\t"
		    : "=&r" (res), "=&r" (oldval)
		    : "r" (&ptr->counter), "r" (old), "r" (new)
		    : "cc");
	} while (res);

	return oldval;
}

should do what you require.

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