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

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Date:	Tue, 29 Apr 2014 09:33:09 +0200
From:	Andreas Herrmann <herrmann.der.user@...glemail.com>
To:	Borislav Petkov <bp@...e.de>
Cc:	Bjorn Helgaas <bhelgaas@...gle.com>,
	Robert Richter <rric@...nel.org>, herrmann.der.user@...il.com,
	Myron Stowe <myron.stowe@...il.com>,
	Myron Stowe <myron.stowe@...hat.com>,
	linux-pci <linux-pci@...r.kernel.org>,
	Suravee Suthikulpanit <suravee.suthikulpanit@....com>,
	Aravind Gopalakrishnan <aravind.gopalakrishnan@....com>,
	kim.naru@....com, Daniel J Blueman <daniel@...ascale.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86 <x86@...nel.org>,
	Steffen Persvold <sp@...ascale.com>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Jan Beulich <JBeulich@...e.com>,
	Yinghai Lu <yinghai@...nel.org>
Subject: Re: [PATCH v2 2/5] x86/PCI: Support additional MMIO range
 capabilities

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
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