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

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Date:	Mon, 28 Apr 2014 23:40:36 +0200
From:	Borislav Petkov <bp@...e.de>
To:	Bjorn Helgaas <bhelgaas@...gle.com>,
	Robert Richter <rric@...nel.org>, herrmann.der.user@...il.com
Cc:	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>,
	Robert Richter <rric@...nel.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 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?

Thanks.

-- 
Regards/Gruss,
    Boris.

Sent from a fat crate under my desk. Formatting is fine.
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