From rlarndt@us.ibm.com  Thu Mar  4 06:52:41 1999
Date: Thu, 4 Mar 1999 08:51:48 -0600
Subject: Item #459: PCI Binding:  More that 256 buses


P1275 Openboot Working Group Proposal -- Proposal #:459 Ver 1

Title:          PCI Binding: More than 256 buses

Author:         Richard L. Arndt

Date:           3 March 99

Ed/Tech:        Technical

Synopsis:       Extend the bus number field in the PCI Physical Address

Doc & Version:  PCI Bus Binding Revision 2.1

Problem:        Server systems are approching the architected limit of
                PCI bus numbers (256).  This is caused by several factors:
                1. Ability to attach many IO drawers on the system SAN
                2. Ability to have several PCI host bridges in an IO drawer
                3. Isolating each PCI slot with a PCI-PCI bridge for error
                   and hot plug isoation.
                4. Adapter cards carry their own PCI-PCI bridges.

Proposal:

        Unfortunately I do not have the background in PCI binding to
understand all of the uses of the current physical address formats.  I
sure that simply using up the 3 spair bits is not adequate.  Making the
physical address 4 cells long would be ok but that leaves a lot of legacy
out in the cold.  Is there some way of introducing a bus group property
that
could be carred along so that large systems could add something and use
the current code?  I would like to discuss this at the 9 March 99 meeting
to set a direction.



[ P1275 Item #459 -- Received: Thu Mar  4 06:52:42 PST 1999 ]