Re: ia64 implementation of lib/iomap.c

David Mosberger
2004-10-26T07:48:56Z

>>>>> On Mon, 25 Oct 2004 10:48:48 -0600, Bjorn Helgaas <bjorn.helgaas@hp.com> said:

Bjorn> On Thursday 21 October 2004 8:34 am, David Mosberger wrote:
>> Is anybody already working on an ia64-version of lib/iomap.c?

Bjorn> Here's a start (also attached, because of the kmail bug that
Bjorn> corrupts whitespace).

Nice!

Bjorn> The idea is that all MMIO iomem cookies are in region 6, so
Bjorn> anything less than that must be a PIO cookie. So we have:

Bjorn> 0xCxxxxxxxxxxxxxxx MMIO cookie (return from ioremap)
Bjorn> 0xRxxxxxxx1SPPPPPP PIO cookie (R=[0-9AB], S=space num, P..P=port)

In reality, `R' is always 0 though, right? Would it be useful to add
the above two lines to asm-ia64/io.h? I think they really help
understanding the code. Perhaps it would also be useful to point out
that the "1" bit is there to catch old/buggy code which attempts to do
an I/O operation on a port without the prerequisite iomap()?

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.

Thanks,

--david