linux-kernel - Re: [patches] [patch 3/5] x86: Add PCI extended config space access for AMD Barcelona

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Date:	Wed, 5 Sep 2007 17:00:27 +0200
From:	"Andreas Herrmann" <andreas.herrmann3@....com>
To:	"H. Peter Anvin" <hpa@...or.com>
cc:	"Arjan van de Ven" <arjan@...radead.org>,
	"Robert Richter" <robert.richter@....com>, patches@...-64.org,
	linux-kernel@...r.kernel.org
Subject: Re: [patches] [patch 3/5] x86: Add PCI extended config space
 access for AMD Barcelona

On Wed, Sep 05, 2007 at 06:58:58AM +0100, H. Peter Anvin wrote:
> Well, they don't add any functionality, do they?

They allow CF8/CFC to access ECS in cases where mmcfg is not working.

> As such, I would agree with Andi -- we only 
> need one method which can (correctly) access the full configuration space,

Right, we need to be able to "correctly access the full config space".

> since it'll look the same on the bus anyway.

Sure, on the bus we should only see pci configuration requests in both
cases.


To summarize it:
- mmcfg needs support by BIOS ("PCI services in ACPI")
- CF8/CFC ECS access does not have that dependency
- For base configuration space access we already have two methods -
  type 1 and mmcfg  (type1 as fallback if there is no mmcfg).
- So what's the benefit in not allowing CF8/CFC ECS  access ("extended type1")
  if the hardware supports it and if mmcfg is not suitable?


One thing that comes out of that fruitless discussion:
For IBS Robert might have to implement CF8/CFC ECS access directly in the IBS
code, or in a new driver for ECS access of NB functions. Just to ensure that
IBS is working if there is no mmcfg. And this is kind of ugly.


Regards,

Andreas

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