From mboxrd@z Thu Jan  1 00:00:00 1970
From: David.Laight@ACULAB.COM (David Laight)
Date: Mon, 6 Mar 2017 15:58:27 +0000
Subject: Panic in quirk_usb_early_handoff
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> From: Mason
> Sent: 06 March 2017 15:46
...
> >> The issue was that, on this platform, the PCI configuration space
> >> and memory space are multiplexed; in other words they reside at
> >> the same physical address, with a bit in MMIO to choose one or
> >> the other.
> >
> > Time to shoot another hardware engineer.
> 
> He's in CC :-)
> 
> > Hopefully it isn't an SMP system - but I wouldn't put it past them.
> 
> This is a dual- and quad- Cortex A9 MP platform :-(

So to do a config space access you have to use a pair of IPIs
to stop the other cpus doing any PCIe data accesses while the
MMIO bit makes the accesses all point to config space.
(After taking a lock to get access to the MMIO register.)

Or has someone a better idea?

	David