[PATCH]: powerpc: clarify use of twi/isync in io macros

[Segher Boessenkool]

> + *
> + * Read operations have additional twi & isync to make sure the read
> + * is actually performed (i.e. the data has come back) before we  
> start
> + * executing any following instructions.
> + *
> + * A data-dependent branch followed by an isync ensures that no
> + * instructions after the isync in program order will be
> + * (speculatively) executed

..."before the isync has completed, and it won't complete until
the branch is resolved;"...

> so the load that the twi depends
> + * on has to complete before anything else is executed; in
> + * particular, it's a barrier to keep MMIO reads ordered before
> + * main-storage accesses.
>   */

You shouldn't post my test and put your signed-off on it, esp.
if I forgot to type half a sentence :-)  Here, have one though:

Signed-off-by: Segher Boessenkool <segher at kernel.crashing.org>



Segher