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

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Date:	Fri, 28 Dec 2007 16:29:50 +1100
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Loic Prylli <loic@...i.com>, Robert Hancock <hancockr@...w.ca>,
	Jeff Garzik <jeff@...zik.org>,
	Arjan van de Ven <arjan@...radead.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	gregkh@...e.de, linux-pci <linux-pci@...ey.karlin.mff.cuni.cz>,
	Martin Mares <mj@....cz>, Matthew Wilcox <matthew@....cx>,
	Kai Ruhnau <kai@...getaschen.dyndns.org>
Subject: Re: [Patch v2] Make PCI extended config space (MMCONFIG) a driver
	opt-in

On Thu, 2007-12-27 at 13:37 -0800, Linus Torvalds wrote:
> The code doesn't actually do what CRS is supposed to help with (ie go
> on 
> to probe another device and then come back to the slow one later), so 
> right now it's pretty much useless *anyway*. 

It's not totally useless... Instead of not seeing the device that hasn't
fully initialized yet at all, we end up waiting a bit and then seeing
it. Going to probe somebody else is a nice optimization we could do with
multithread PCI probe but doesn't remove the need for CRS.

I have embedded boards where proper CRS operations is critical since the
kernel brings the PCIe link up itself, and thus is likely to hit devices
still in the middle of CRS.

Note that I'm -very- surprised however that your BIOS hands control out
of the kernel with devices still issuing CRS... Unless those devices may
do it after boot but that's dodgy and will break many other things.

Ben.

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