On Wednesday, September 15, 2010 03:50:14 pm H. Peter Anvin wrote: > On 09/15/2010 02:09 PM, Bjorn Helgaas wrote: > > > > On the machine above (a Dell T3500), the [mem 0xbff00000-0xbfffffff] region > > doesn't actually work and is likely a BIOS defect. The symptom is that we > > move the AHCI controller to 0xbff00000, which leads to "Boot has failed, > > sleeping forever," a BUG in ahci_stop_engine(), or some other boot failure. > > > > Acked-by: H. Peter Anvin <hpa@xxxxxxxxx> > > ... for the patch in general, but I would like to *also* request a DMA > or PCI quirk to explicitly reserve the above range on the affected Dell > machines. I'd like to do that, but I don't see a good way to do it yet. We saw the problem on a T3500, a T3400, and a T4500, and I'm sure there are others. So I don't know how to identify the affected machines. And I don't know how to identify the invalid ranges, because I suspect it depends on the memory size. I think it would be quite unusual for a window to start 1MB under the nice 256MB boundary, but I'm not sure I'm ready to say that's always illegal. On these machines, the [mem 0xbff00000-0xbfffffff] area is actually reported as reserved in the E820 map, and I first thought we could simply rely on that. But I'm not really comfortable with that either, because I don't think there's a dependable relationship between those E820 entries and ACPI and PCI devices. For one thing, I experimented with Windows, and it happily places PCI devices in reserved areas, and I think we're likely to trip over more BIOS bugs if we rely on something Windows doesn't. I suspect Windows would blow up, too, if we could somehow fill up the rest of the window and force it to allocate the bottom. But since it's only a 1MB area, I think that would be very difficult to do unless there's some way to tweak PCI BARs before booting Windows. Bjorn -- 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
