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Date:   Fri, 6 May 2022 14:15:00 +0100 (BST)
From:   "Maciej W. Rozycki" <macro@orcam.me.uk>
To:     David Laight <David.Laight@ACULAB.COM>
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Subject: RE: [RFC v2 01/39] Kconfig: introduce HAS_IOPORT option and select
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On Fri, 6 May 2022, David Laight wrote:

> >  The PCI configuration space was retrofitted into x86 systems (and is
> > accessed in an awkward manner with them), but with a new design such a
> > clean approach is most welcome IMHO.  Thank you for your explanation.
> 
> Actually I think x86 was the initial system for PCI.
> The PCI config space 'mess' is all about trying to make
> something that wouldn't break existing memory maps.

 It was retrofitted in that x86 systems already existed for ~15 years when 
PCI came into picture.  Therefore the makers of the CPU ISA couldn't have 
envisaged the need for config access instructions like they did for memory 
and port access.

  Maciej