On Wed, 2010-03-17 at 17:47 +0900, Kenji Kaneshige wrote: > Bjorn Helgaas wrote: > > On Wed, 2010-03-17 at 12:25 +0900, Kenji Kaneshige wrote: > >> Bjorn Helgaas wrote: > >>> Yanko's GA-MA78GM-S2H (BIOS F11) reports a host bridge window that overlaps > >>> system memory: > >>> > >>> PCI window: [mem 0xcff00000-0x10ed0ffff] > >>> System RAM: [mem 0x100000000-0x22fffffff] > >>> > >>> We can be pretty confident that the System RAM region is correct (if it > >>> were wrong, we'd crash as soon as we tried to use any memory in that area), > >>> so this patch tries to correct the PCI window by trimming it so it doesn't > >>> conflict with any previous reservations. > >> Though I might misunderstand something, it looks Yanko's machine specific > >> workaround. I'm wondering if trimming _CRS is a generic workaround for > >> broken _CRS machine. > >> > >> How about doing this when GA-MA78GM-S2H (BIOS F11) (and known machines > >> that have the same problem) is detected? Or how about switching nocrs > >> mode if the problem (resource conflict) is detected? > > > > It's certainly a possibility to do this only for specific machines, but > > I'd like to avoid tripping over issues one-by-one. > > > > I think there are three ways to address BIOS _CRS defects: > > > > 1) Ship an OEM-specific host bridge driver > > 2) Put a platform- or BIOS-specific quirk into Windows > > "into Linux"? No, I forgot to say that all this is my speculation about how Windows works. I really can't imagine OEMs shipping OEM-specific host bridge drivers for Windows, because I think it would make it to painful to install. And I don't think Windows quirks would really be practical either, because it would take so long for a new Windows release containing the quirk to appear that the OEM could never wait for it. So I think that if we can make Linux parse _CRS in the same way Window does, we should be able to handle most or all machines in the field without a lot of quirks. Of course, this is all pure speculation on my part; I've never worked on Windows. Bjorn > > 3) Change the BIOS > > > > The first two sound like such a hassle to me that I doubt they would be > > practical. > > I agree. > For 1), we need OEM-specific driver, not chipset specific driver. > > For 2), I thought it depends on how many machines with broken _CRS are > there, and I didn't think there are so many, but... > > > > > But it's clear that there are systems like this with what appear to be > > _CRS defects. It's quite possible that it's not really a defect, and we > > just don't understand how to parse _CRS correctly yet. Or, Windows > > might have a few heuristics to clean up obvious errors. > > Indeed, it might be true. Now I realize I need to change my opinion > about 2). > > > > > For example, I think Windows aligns host bridge windows, as documented > > here: http://bugzilla.kernel.org/show_bug.cgi?id=14337 > > > > I think Windows also knows to ignore the Consumer/Producer bit in > > Address Space Descriptors, and assume that all resources on bridges are > > Producers. > > > > Hmm, what we really need is a way to run Windows in a virtualized > > environment where we could manipulate the _CRS method and see what > > Windows does with it... > > > > Anyway, I'd like to make Linux behave as much like Windows as possible > > in this area so we can take advantage of all the testing that's done > > with Windows. > > Okey, thank you very much for explanation. I understood the background > of your change. > > Thanks, > Kenji Kaneshige > > > -- 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
