Re: [PATCH v2 2/5] x86/PCI: Support additional MMIO range capabilities

[Andreas Herrmann <herrmann.der.user@googlemail.com>]

On Mon, Apr 28, 2014 at 11:40:36PM +0200, Borislav Petkov wrote:
> On Mon, Apr 28, 2014 at 02:50:29PM -0600, Bjorn Helgaas wrote:
> > This I/O ECS thing seems likely to cause future problems.  My
> > understanding (based on sec 2.8 of [1]) is that enable_pci_io_ecs()
> > and pci_enable_pci_io_ecs() are there to enable access to extended
> > config space (offsets 256-4095) via the 0xcf8/0xcfc I/O ports.
> > 
> > Per sec 4.1.1 of [2], we should be using ECAM (the memory-mapped
> > enhanced configuration mechanism, i.e., MMCONFIG) to access extended
> > config space, and the BIOS should supply an MCFG table.
> > 
> > So why do we need to enable I/O access to ECS on AMD chips at all?  Is
> > this a workaround for a broken BIOS that doesn't supply an MCFG table?
> 
> That's a good question. 831d991821dae doesn't say but I have a hunch
> Andreas and/or Robert should know. I seem to vaguely remember it
> might've been because of a missing MCFG but have flushed it out of the
> cache long time ago.
> 
> Let's ask them.
> 
> Andreas, Robert, guys, do you remember why we did the PCI IO ECS access?
> B0rked BIOSes?


I am sure, it's because some server systems had MMIO ECS access not
enabled in BIOS. I can't remember which systems were affected.


Andreas