On Wednesday 27 January 2010 09:53:37 am Jesse Barnes wrote: > On Wed, 27 Jan 2010 09:45:15 -0700 > Bjorn Helgaas <bjorn.helgaas@xxxxxx> 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)? Without intel_bus.c, we essentially assume config 1 all the time. If we keep intel_bus.c and this patch for .33, things should work for configs 1 and 4. Adding support for config 4 is good. The bad part is that for config 4, intel_bus.c covers up any defects in the _CRS or the Linux code that interprets it. The reason Yinghai added intel_bus.c in the first place was to work around a defect in this area[1]. Keeping it will make it harder to fix the underlying issue that keeps us from turning on _CRS for that box. Bjorn [1] http://lkml.org/lkml/2009/10/6/371 -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
