Re: [patch 1/2] powerpc: rmb fix

[Segher Boessenkool <segher@kernel.crashing.org>]

>>  #define mb()   __asm__ __volatile__ ("sync" : : : "memory")
>> -#define rmb()  __asm__ __volatile__ (__stringify(LWSYNC) : : : 
>> "memory")
>> +#define rmb()  __asm__ __volatile__ ("sync" : : : "memory")
>>  #define wmb()  __asm__ __volatile__ ("sync" : : : "memory")
>>  #define read_barrier_depends()  do { } while(0)
>>
>> @@ -42,7 +42,7 @@
>>  #ifdef __KERNEL__
>>  #ifdef CONFIG_SMP
>>  #define smp_mb()	mb()
>> -#define smp_rmb()	rmb()
>> +#define smp_rmb()	__asm__ __volatile__ (__stringify(LWSYNC) : : : 
>> "memory")
>>  #define smp_wmb()	eieio()
>>  #define smp_read_barrier_depends()	read_barrier_depends()
>>  #else
>
> I had to think about this one for awhile.  It looks at first glance to 
> be the right
> thing to do.  But I do wonder how long rmb() has been lwsync

Since the {ppc,ppc64} -> powerpc merge.

> and if as a practical matter that has caused any problems?

It has not as far as I know.

> If this isn't causing any problems maybe there
> is some loigic we are overlooking?

The I/O accessor functions enforce the necessary ordering
already I believe.


Segher