Re: [PATCH v5 03/18] pci: isolated address space for PCI bus

[Michael S. Tsirkin]

On Wed, Feb 02, 2022 at 09:30:42AM +0000, Peter Maydell wrote:
> > I/O port space is always the identity mapped CPU address space unless
> > sparse translations are used to create multiple I/O port spaces (not
> > implemented).  I/O port space is only accessed by the CPU, there are no
> > device initiated I/O port transactions, so the address space relative
> > to the device is irrelevant.
> 
> Does the PCI spec actually forbid any master except the CPU from
> issuing I/O port transactions, or is it just that in practice nobody
> makes a PCI device that does weird stuff like that ?
> 
> thanks
> -- PMM

Hmm, the only thing vaguely related in the spec that I know of is this:

        PCI Express supports I/O Space for compatibility with legacy devices 
which require their use.
        Future revisions of this specification may deprecate the use of I/O 
Space.

Alex, what did you refer to?

-- 
MST