Splitting hardware access out of xserver (in/out, int10, xf86emu)

Adam Jackson ajax at nwnk.net
Tue Oct 27 10:35:45 PDT 2009

On Tue, 2009-10-27 at 16:56 +0100, Mark Kettenis wrote:

> That said, the way in/out are used in the xserver and associated (PCI)
> drivers is really bogus.  Their usage should be replaced by a
> mechanism similar to how memory mapped io is handled.  PCI drivers
> should really use pci_device_map_range() to "map" io space just like
> mmio space such that they can work on architectures that have multiple
> PCI domains.

While domainful PCI chipsets typically provide this functionality,
normal x86 kit does not.  There's no especially good way to emulate it
either, since even if the segfault handler told you i/o direction you'd
still need to know the instruction length in the general case.

So, no, you really can't force memory mapped i/o space access and still
remain portable to x86, at least not without adding a modest amount of
code to the kernel.

- ajax
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