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

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Message-ID: <alpine.LFD.0.9999.0712272135270.21557@woody.linux-foundation.org>
Date:	Thu, 27 Dec 2007 21:37:49 -0800 (PST)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Benjamin Herrenschmidt <benh@...nel.crashing.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 Fri, 28 Dec 2007, Benjamin Herrenschmidt wrote:
> 
> 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.

.. but that's perfectly fine. A PCI-E bridge will certainly retry it in 
hardware (or it isn't a PCI-E bridge!).

The CRS bit in question is purely the *software*visible* bit - ie whether 
the OS gets told about the delay or not. As long as the OS then just 
retries the same device, enabling CRS SV is pointless.

So I'm going to disable that thing. If there is some _other_ PCI-E bridge 
that is simply buggy, and cannot handle the hw retry itself or is just 
otherwise dodgy, we can have a white-list for cases where it really needs 
to be done, but the current code is just bogus.

			Linus
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