linux-kernel - Re: [Patch v2] Make PCI extended config space (MMCONFIG) a driver opt-in

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Message-ID: <20071228211219.GA10475@jurassic.park.msu.ru>
Date:	Sat, 29 Dec 2007 00:12:19 +0300
From:	Ivan Kokshaysky <ink@...assic.park.msu.ru>
To:	Loic Prylli <loic@...i.com>
Cc:	Arjan van de Ven <arjan@...radead.org>,
	Daniel Barkalow <barkalow@...ervon.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Kai Ruhnau <kai@...getaschen.dyndns.org>,
	Robert Hancock <hancockr@...w.ca>,
	Jeff Garzik <jeff@...zik.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	gregkh@...e.de, linux-pci <linux-pci@...ey.karlin.mff.cuni.cz>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Martin Mares <mj@....cz>, Matthew Wilcox <matthew@....cx>
Subject: Re: [Patch v2] Make PCI extended config space (MMCONFIG) a driver
	opt-in

On Fri, Dec 28, 2007 at 12:40:53PM -0500, Loic Prylli wrote:
> The only quirk I see removed is a bitmap with an arbitrary size (that we
> don't really know is sufficient for every system), and that is only
> built using comparison between mmconf and type1 accesses.  IMHO, there
> is zero knowledge in that removed code (no knowledge about specific
> chipsets that work or don't work, or misleading BIOSes).

Precisely.

As a side note: that code also has zero knowledge about what the generic
PCI probe code can do later, like it fails to detect this ATI/CRS breakage.

> One thing that could be changed in pci_cfg_space_size() is to avoid
> making a special case for PCI-X 266MHz/533Mhz (assume cfg_size == 256
> for such devices too, reserve extended cfg-space for pci-express
> devices). There is good reasons to think no such PCI-X 266Mhz/533 device
> will ever have an extended-space (no capability IDs was ever defined in
> the PCI-X 2.0 spec, no new revision is planned). Such a check would
> avoid the possibility of trying extended-conf-space access for PCI-X 2.0
> devices behind a amd-8132 or similar (such accesses would just returnd
> -1, but there was some objections raised about doing anything like that
> other than at initialization time, even if there is ample reasons to
> argue it would be harmless).

I agree, we should remove it. IIRC, this PCI-X check was written
long ago with some draft (not a final spec) in hands. Matthew?

Ivan.
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