Re: [Qemu-devel] Re: [PATCH 1/6] Make config space accessor host bus trapable

[Benjamin Herrenschmidt <benh@kernel.crashing.org>]

On Mon, 2010-01-04 at 23:12 +0200, Michael S. Tsirkin wrote:
> Well, the main issue if I understand correcttly is that basically the
> same hardware bridge can be connected to host in different ways. Yes, we
> can say "if it's connected differently it's a different device" but this
> is slightly ugly, device should not have to know how it's connected. It
> would be cleaner to have a "connector" device in the middle that swaps
> bytes.  Even though yes, what you describe would be less ugly than using
> proprocessor as we do now.

Well, the thing is... PCI is always little endian. I'm not 100% familiar
on how emulation of devices works in qemu, but it's possible that the
problem here is simply not how a standard PCI host bridge is connected
to the processor changing but rather whether it's connected to an x86
host or a ppc host should make the byte order appear different. IE. a
PPC operating system will byteswap accesses. If qemu just passes on
accesses -as-is- instead of doing natural byteswapping then indeed you
will need that added swap there too.

I still think though that this should be buried in the accessors for the
host bridge themselves, eventually controlled by a flag set when
instanciating the host bridge in case it can indeed be wired in
different ways.

Cheers,
Ben.