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

From: Sinan Kaya <okaya@kernel.org>
To: Alex_Gagniuc@Dellteam.com, mr.nuke.me@gmail.com, keith.busch@intel.com
Cc: baicar.tyler@gmail.com, sbobroff@linux.ibm.com,
	linux-pci@vger.kernel.org, rjw@rjwysocki.net,
	linux-kernel@vger.kernel.org, Shyam.Iyer@dell.com,
	linux-acpi@vger.kernel.org, lukas@wunner.de, oohall@gmail.com,
	Austin.Bolen@dell.com, bhelgaas@google.com,
	linuxppc-dev@lists.ozlabs.org, lenb@kernel.org
Subject: Re: [PATCH 0/2] PCI/AER: Consistently use _OSC to determine who owns AER
Date: Mon, 19 Nov 2018 15:33:52 -0500	[thread overview]
Message-ID: <84013a8a-287d-d700-6710-91cc35f507c8@kernel.org> (raw)
In-Reply-To: <bb575cfdcd0a4c50b489fb16eccfbff2@ausx13mps321.AMER.DELL.COM>

On 11/19/2018 3:16 PM, Alex_Gagniuc@Dellteam.com 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
> 