Re: [RFC PATCH 1/3] add generic hypercall support

Hollis Blanchard
2009-05-05T17:03:21Z

On Tue, 2009-05-05 at 09:24 -0400, Gregory Haskins wrote:
>
> *) PIO is more direct than MMIO, but it poses other problems such as:
> a) can have a small limited address space (x86 is 2^16)
> b) is a narrow-band interface (one 8, 16, 32, 64 bit word at a time)
> c) not available on all archs (PCI mentions ppc as problematic) and
> is therefore recommended to avoid.

Side note: I don't know what PCI has to do with this, and "problematic"
isn't the word I would use. ;) As far as I know, x86 is the only
still-alive architecture that implements instructions for a separate IO
space (not even ia64 does).

--
Hollis Blanchard
IBM Linux Technology Center