[PATCH 1/3] powerpc/mpc85xx: remove the unneeded pci init functions for corenet ds board

[Scott Wood]

On 05/31/2013 01:43:49 AM, Kevin Hao wrote:
> On Thu, May 30, 2013 at 01:54:59PM -0500, Scott Wood wrote:
> > On 05/30/2013 05:20:34 AM, Kevin Hao wrote:
> > >On Tue, May 28, 2013 at 05:52:09PM -0500, Scott Wood wrote:
> > >> On 05/21/2013 07:04:58 AM, Kevin Hao wrote:
> > >> >It also seems that we don't support ISA on all the current
> > >corenet ds
> > >> >boards. So picking a primary bus seems useless, remove that
> > >function
> > >> >too.
> > >>
> > >> IIRC that was due to some bugs in the PPC PCI code in the  
> absence of
> > >> any primary bus.
> > >
> > >Do you know more about these bugs?
> >
> > Not off the top of my head -- either search the archives or ask Ben.
> >
> > >>  fsl_pci_assign_primary() will arbitrarily pick one
> > >> to be primary if there's no ISA.  Have the bugs been fixed?
> > >
> > >I know there should be some reason that we put the
> > >fsl_pci_assign_primary()
> > >here. But frankly I am not sure what bugs this workaround try to
> > >fix. For these
> > >corenet boards picking one to be primary has no effect to the
> > >64bit kernel.
> > >And for 32bit kernel, the only effect of this is that isa_io_base
> > >is set to the
> > >io virtual base of the primary bus. But the isa_io_base only make
> > >sense when
> > >we do have a isa bus, so that we can access some well-known io
> > >ports directly
> > >by using outx/inx. But if we don't have isa bus on the board, the
> > >value of
> > >isa_io_base should make no sense at all. So we really don't need
> > >to pick a
> > >fake primary bus. Of course I may miss something, correct me if I
> > >am wrong. :-)
> >
> > outx/inx can also be used for PCI I/O BARs.
> 
> Yes, I know there is also PIO. But the value of isa_io_base doesn't
> have any effect for this.

See this e-mail for some of the issues I was referring to with  
isa_io_base being zero:
https://lists.ozlabs.org/pipermail/linuxppc-dev/2012-June/098586.html

Reading it again I'm not so sure that the problem is so much that we  
need a primary, as that somewhat bad things happen on non-primary  
buses, such as the possibility of assigning a zero BAR.  Some hardware  
(including QEMU's PCI emulation) cares about this, though most  
doesn't.  We only have one PCI bus under QEMU, so when we started  
picking an arbitrary bus to be primary, the problem went away because  
there was only one bus and therefore there was no non-primary bus.

-Scott