Re: ia64 implementation of lib/iomap.c

Jesse Barnes
2004-10-26T16:23:24Z

On Tuesday, October 26, 2004 12:48 am, David Mosberger wrote:
> Bjorn> I heard a rumor that ioreadX() on PIO cookies is supposed to
> Bjorn> have looser semantics than inX() on the port, so we might be
> Bjorn> able to get away without the memory fence in inb(). But I
> Bjorn> can't substantiate that, so this keeps the generic behavior
> Bjorn> of ioreadX() and inX() having identical semantics for PIO.
>
> Can somebody confirm? Dropping the mf.a from ioreadX() for I/O port
> accesses would save lots of cycles. Though I guess most
> high-performance devices are smart enough to stay away from I/O port
> space nowadays, so perhaps it doesn't matter in reality.

I'm pretty sure this is the case. In fact when I last discussed this with
Linus he indicated that an ioread shouldn't guarantee DMA completion either,
which would mean we could reuse the read_relaxed stuff to implement it.

Jesse