Re: [PATCH 0/2] PCI/AER: Consistently use _OSC to determine who owns AER

[Sinan Kaya]

On 11/19/2018 3:16 PM, Alex_Gagniuc@xxxxxxxxxxxx wrote:
> On 11/19/2018 01:32 PM, Sinan Kaya wrote:
> > ACPI 6.2:
> >
> > 18.3.2.4 PCI Express Root Port AER Structure
> >
> > Flags:
> >
> > Bit [0] - FIRMWARE_FIRST: If set, this bit indicates to the OSPM that system
> > firmware will handle errors from this source first.
> > Bit [1] - GLOBAL: If set, indicates that the settings contained in this
> > structure apply globally to all PCI Express Devices.
> > All other bits must be set to zero.
> >
> > It doesn't say shall, may or might. It says will.
>
> It says "system firmware will handle errors". It does not say "system
> firmware owns AER registers". In absence on any descriptor text on the
> meaning of these tables, this really looks to me like it should be
> interpreted as a descriptor of APEI error sources, not a mutex on who
> writes to certain bits-- AER in this case.

True. I was trying to get it out in a rush. I omitted words.

However; table assumes governance about for which entities firmware first
should be enabled. There is no cross reference to _OSC or permission
negotiation like _OST.

> I don't think that is contradictory or inconsistent.
> I also wasn't able to find any reference to HEST in UEFI 2.7, only in
> ACPI spec.

You are right. It was a confusion on my side. The right place to look is
ACPI specification. I was involved in this a couple of years ago. Some pieces
were in UEFI spec. Other pieces were in ACPI. I guess they got unified
now.

> > I think It depends on your PCI topology.
> >
> > For other topologies with multiple PCI root complexes, I can see this being
> > used per root complex flag to indicate which root complex needs firmware first
> > and which one doesn't.
>
> _OSC is per root bus, so it's already granular enough, right? Why would
> it depend on PCI topology?

I was speculating. I don't have the full background on this. Need to consult
the spec developers.

> > As I said in my previous email, the right place to talk about this is UEFI
> > forum.
>
> The way I would present the problem to he spec writers is that, although
> the spec appears to be consistent, we've seen firmware vendors that made
> the wrong assumptions about HEST/_OSC. Instead of describing AER
> ownership with _OSC, they attempted to do it with HEST. So we should add
> an implementation note, or clarification about this.

I agree.

> Alex