Re: [PATCH] pci-mmconfig fix for 2.6.9

[Andi Kleen <ak@suse.de>]

On Sun, Nov 14, 2004 at 11:00:21PM -0700, Grant Grundler wrote:
> > writes to handle Michael's power management issue properly. 
> > That would be definitely the safer approach.
> 
> hrm...are you suggesting another entry point in the struct raw_pci_ops?

Yes.

> 
> There are two tests in arch/i386/pci/mmconfig.c:pci_mmcfg_init() before
> the raw_pci_ops is set to &pci_mmcfg. Perhaps some additional crude tests
> could select a different set of pci_raw_ops to deal with posted writes
> to mmconfig space. Someone more familiar with those chipsets might
> find a more elegant solution.

I cannot think of a generic good way to detect posting from the software
side.

> 
> > > That means someone has to introduce a new method to access
> > > mmconfig if they implement postable writes.
> > 
> > 
> > Problem is that it adds silently a very subtle bug and there
> > is no way I know of for ACPI to tell the firmware it shouldn't use
> > posting.
> 
> Uhm, ACPI needs to tell the firmware?
> I would expect firmware to be platform/chip specific and "just know".

x86-64 always uses direct hardware access, x86 can use the 32bit PCI BIOS,
but it's now discouraged. 


> 
> If you meant OS, we already embed knowledge about specific chipsets
> for bug workarounds (e.g. tg3 driver). I think that's an option here too.
> I mean tweaking mmconfig.c to install a (possibly) chip specific
> method (raw_pci_ops) to flush posted mmconfig writes.

Possibly yes.  One issue is that we have a subtle bug until we notice
though. 

-Andi