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Date: Wed, 27 Jan 2010 08:53:37 -0800 From: Jesse Barnes <jbarnes@...tuousgeek.org> To: Bjorn Helgaas <bjorn.helgaas@...com> Cc: Yinghai Lu <yinghai@...nel.org>, Jeff Garrett <jeff@...rrett.org>, "Rafael J. Wysocki" <rjw@...k.pl>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, Kernel Testers List <kernel-testers@...r.kernel.org>, Linux PCI <linux-pci@...r.kernel.org>, Linus Torvalds <torvalds@...ux-foundation.org>, Myron Stowe <myron.stowe@...com>, Matthew Garrett <mjg59@...f.ucam.org>, Ingo Molnar <mingo@...e.hu> Subject: Re: [Bug #15124] PCI host bridge windows ignored (works with pci=use_crs) On Wed, 27 Jan 2010 09:45:15 -0700 Bjorn Helgaas <bjorn.helgaas@...com> wrote: > On Tuesday 26 January 2010 03:57:31 pm Yinghai Lu wrote: > > [PATCH] x86/pci: don't use ioh resource if only have one ioh > > > > some system could use reosurce out of IOH resources when only one ioh is there. > > > > could be BIOS have wrong IOH resources and not enable them. > > The subtractive decode theory makes sense and would explain what's > happening, but I don't like this patch. > > If we assume that this really is a subtractive decode issue, this > patch approaches it the wrong way. We need to know whether a > particular host bridge is configured for subtractive decode. This > patch tests whether we have more than one host bridge, which is quite > a different question. > > Imagine these system configurations: > > 1) a single host bridge with subtractive decode > 2) a single host bridge with only positive decode > 3) multiple host bridges with subtractive decode enabled on one > 4) multiple host bridges with only positive decode > > This patch will break if we encounter configs 2 or 3. In config 2, > this patch assumes the bridge performs subtractive decode, so we > think the bridge forwards more address space than it actually does. > If we try to use that address space, the device will never see the > accesses. In config 3, this patch assumes there's no subtractive > decode, so we would see Jeff's problem all over again. Right, but OTOH: - multiple IOH has already been tested with the intel_bus.c code - we want to move to using _CRS data in these cases instead So do you have any objection to applying this patch for 2.6.33 and then moving away from intel_bus.c in .34 (assuming we can get _CRS working well on the same machines where intel_bus.c was needed)? -- Jesse Barnes, Intel Open Source Technology Center -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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