linux-kernel - Re: [PATCH V5 3/4] x86/PCI: Stop enabling ECS for AMD CPUs after Fam16h

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Date:	Fri, 23 May 2014 13:56:22 +0200
From:	Robert Richter <rric@...nel.org>
To:	Bjorn Helgaas <bhelgaas@...gle.com>
Cc:	Suravee Suthikulanit <suravee.suthikulpanit@....com>,
	Borislav Petkov <bp@...en8.de>,
	Daniel J Blueman <daniel@...ascale.com>,
	Andreas Herrmann <herrmann.der.user@...glemail.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Aravind Gopalakrishnan <Aravind.Gopalakrishnan@....com>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	Borislav Petkov <bp@...e.de>,
	Myron Stowe <myron.stowe@...hat.com>
Subject: Re: [PATCH V5 3/4] x86/PCI: Stop enabling ECS for AMD CPUs after
 Fam16h

On 22.05.14 20:54:54, Bjorn Helgaas wrote:
> I'm going to go out on a limb and guess that Windows does not enable
> ECS, so it probably uses ECAM.  Therefore, I suspect Linux's parsing
> of MCFG is broken in some way, and we probably *could* use ECAM in all
> these cases I'm seeing.

Even if ECS is not enabled the system should be fine anyway, as ECS is
only used to enable certain features. For family 10h this was
originally the IBS EILVT (extended interrupt local vector table,
needed for hw profiling) setup which need to be set by the OS which
the BIOS didn't right. This should be fixed now and properly set by
the BIOS on 15h+ systems.

I don't remember what was added to 16h where ECS was needed, I think
there was one (Suravee?). Not sure if this is essential.

So using MCFG should be fine, since if in the rare case when it is
broken, the system should work properly anyway without it and only
some special features, if any, do not work anymore (e.g. IBS should
work fine).

-Robert
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