Hi Guo,
> +/*
> + * set_bit - Atomically set a bit in memory
> + * @nr: the bit to set
> + * @addr: the address to start counting from
> + *
> + * This function is atomic and may not be reordered. See __set_bit()
> + * if you do not require the atomic guarantees.
> + *
> + * Note: there are no guarantees that this function will not be reordered
> + * on non x86 architectures, so if you are writing portable code,
> + * make sure not to rely on its reordering guarantees.
> + *
> + * Note that @nr may be almost arbitrarily large; this function is not
> + * restricted to acting on a single-word quantity.
> + */
> +static inline void set_bit(int nr, volatile unsigned long *addr)
> +{
> + unsigned long mask = BIT_MASK(nr);
> + unsigned long *p = ((unsigned long *)addr) + BIT_WORD(nr);
> + unsigned long tmp;
> +
> + /* *p |= mask; */
> + smp_mb();
> + asm volatile (
> + "1: ldex.w %0, (%2) \n"
> + " or32 %0, %0, %1 \n"
> + " stex.w %0, (%2) \n"
> + " bez %0, 1b \n"
> + : "=&r"(tmp)
> + : "r"(mask), "r"(p)
> + : "memory");
> + smp_mb();
> +}
> +
> +/**
> + * clear_bit - Clears a bit in memory
> + * @nr: Bit to clear
> + * @addr: Address to start counting from
> + *
> + * clear_bit() is atomic and may not be reordered. However, it does
> + * not contain a memory barrier, so if it is used for locking purposes,
> + * you should call smp_mb__before_atomic() and/or smp_mb__after_atomic()
> + * in order to ensure changes are visible on other processors.
> + */
> +static inline void clear_bit(int nr, volatile unsigned long *addr)
> +{
> + unsigned long mask = BIT_MASK(nr);
> + unsigned long *p = ((unsigned long *)addr) + BIT_WORD(nr);
> + unsigned long tmp;
> +
> + /* *p &= ~mask; */
> + mask = ~mask;
> + smp_mb();
> + asm volatile (
> + "1: ldex.w %0, (%2) \n"
> + " and32 %0, %0, %1 \n"
> + " stex.w %0, (%2) \n"
> + " bez %0, 1b \n"
> + : "=&r"(tmp)
> + : "r"(mask), "r"(p)
> + : "memory");
> + smp_mb();
> +}
> +
> +/**
> + * change_bit - Toggle a bit in memory
> + * @nr: Bit to change
> + * @addr: Address to start counting from
> + *
> + * change_bit() is atomic and may not be reordered. It may be
> + * reordered on other architectures than x86.
> + * Note that @nr may be almost arbitrarily large; this function is not
> + * restricted to acting on a single-word quantity.
> + */
> +static inline void change_bit(int nr, volatile unsigned long *addr)
> +{
> + unsigned long mask = BIT_MASK(nr);
> + unsigned long *p = ((unsigned long *)addr) + BIT_WORD(nr);
> + unsigned long tmp;
> +
> + /* *p ^= mask; */
> + smp_mb();
> + asm volatile (
> + "1: ldex.w %0, (%2) \n"
> + " xor32 %0, %0, %1 \n"
> + " stex.w %0, (%2) \n"
> + " bez %0, 1b \n"
> + : "=&r"(tmp)
> + : "r"(mask), "r"(p)
> + : "memory");
> + smp_mb();
> +}
The {set,clear,change}_bit() operations don't have to be ordered: you
might want to remove the above smp_mb()s (and adjust the comments).
Andrea
