From: Maciej W. Rozycki > Sent: 06 May 2022 14:15 > 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. Rev 2.0 of the PCI spec (1993) defines two mechanisms for config cycles. #2 is probably the first one and maps all of PCI config space into 4k of IO space (PCI bridges aren't supported). #1 requires a pair of accesses (and SMP locking). Neither is really horrid. For horrid try the ISApnp interface. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
