[PATCH]: powerpc documentation: Clarify why twi appears in the i/o macros.

[Segher Boessenkool]

>> + * A data-dependent branch followed by an isync ensures that no
>
> I think it's potentially confusing to talk about data-dependent
> branches when what the code does is a twi instruction.  Even if you
> argue that a twi is a data-dependent branch (and I disagree with that,
> since a trap is not a branch),

If you argue it is *not* a branch, where in the architecture
documentation can we find any language that gives us the
guarantee we depend on here?

> that wouldn't be obvious to a casual
> reader of the code.

True enough.

> In other words, I don't think the comment
> clarifies the situation very much.

Got anything better?  :-)

The first half of the new comment probably should go in no
matter what (it says what twi;isync do here, not how exactly
that works).


Segher