Re: [PATCH 3/3] Add NumaChip quirk

From: Arne Georg Gleditsch
Date: Tue Oct 25 2011 - 15:03:22 EST

On 25. okt. 2011 19:33, Steffen Persvold wrote:
> On 10/25/2011 19:15, Bjorn Helgaas wrote:
>> NumaChip sounds like an exception because you know you never care
>> about using those BARs. But I'm curious -- it looks like Linux didn't
>> even try to assign resources to them. I thought something in the
>> pci_assign_unassigned_resources() path would have tried to do
>> something with them. If we *did* assign resources to those BARs, I
>> assume nothing would break, since there's no driver that actually uses
>> them. Right?
> Correct, the BARs are there and if something sensible were written to
> them (and MemorySpace was enabled in the Command register) NumaChip
> *would* respond to mmio accesses to that address range.

A minor point: adjusting the BARs would not strictly speaking be
sufficient for the NumaChip to respond, as it would never see these
accesses unless the [MMIO address range]->[HyperTransport node/link]
registers of the CPU NorthBridges were also updated with the relevant
ranges. This is a bit messy, but in a way much the same issue as when
secondary southbridges are connected to secondary CPUs in any other
HyperTransport-based system.

Perhaps an alternative to this NumaChip-specific quirk would be to
special-case BARs belonging to "PCI" devices 00:18 - 00:1f in AMD
Opteron systems. These always indicate coherent HT devices and fiddling
with the CPU NB maps are going to be required if anything is changed
regarding the BAR assignments here.

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