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

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Date:	Thu, 27 Dec 2007 06:52:35 -0500
From:	Jeff Garzik <jeff@...zik.org>
To:	Arjan van de Ven <arjan@...radead.org>
CC:	linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>, gregkh@...e.de,
	inux-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

Arjan van de Ven wrote:
> This patch also adds a sysfs property for each device into which root can
> write a '1' to enable extended configuration space. The kernel will print
> a notice into dmesg when this happens (including the name of the app) so that
> if the system crashes as a result of this action, the user can know what
> action/tool caused it.

Comments:

1) [minor] With a bit in struct pci_dev, there is no need for separate 
raw_pci_ops.  That will simplify your patch, with no functionality change.

"golden" arches (no pun intended) may implement raw_pci_ops that 
_always_ work with extended config space, and simply ignore that bit, if 
that is how their underlying non-mmconfig-nor-type1 hardware is implemented.

2) [non-minor] hmmmm.

	[jgarzik@...e ~]$ lspci -n | wc -l
	23

So I would have to perform 23 sysfs twiddles, before I could obtain a 
full and unabridged 'lspci -vvvxxx'?

For the userspace interface, the most-often-used knob for diagnostic 
purposes will be the easiest one.  And that's

	echo 1 > enable-ext-cfg-space-for-all-buses-ACPI-says-to
	lspci -vvvxxx

3) [minor] architectures must be able to override 
pci_enable_ext_config().  see "golden arches".

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