On Thu, Dec 05, 2013 at 05:19:47PM -0700, Bjorn Helgaas wrote: > pci_bridge_check_ranges() determines whether the bridge supports an I/O > aperture and a prefetchable memory aperture. > > Previously, if the I/O aperture was unsupported, disabled, or configured at > [io 0x0000-0x0fff], we wrote 0xf0 to PCI_IO_BASE and PCI_IO_LIMIT, which, > if the bridge supports it, enables the I/O aperture at [io 0xf000-0xffff]. > The enabled aperture may conflict with other devices in the system. > > Similarly, we wrote 0xfff0 to PCI_PREF_MEMORY_BASE and > PCI_PREF_MEMORY_LIMIT, which enables the prefetchable memory aperture at > [mem 0xfff00000-0xffffffff], and that may also conflict with other devices. > > All we need to know is whether the base and limit registers are writable, > so we can use values that leave the apertures disabled, e.g., PCI_IO_BASE = > 0xf0, PCI_IO_LIMIT = 0xe0, PCI_PREF_MEMORY_BASE = 0xfff0, > PCI_PREF_MEMORY_LIMIT = 0xffe0. > > Writing non-zero values to both the base and limit registers means we > detect whether either or both are writable, as we did before. Looks sane to me. The only refinement would be to detect if IO is enabled and use that as a first check. Cheers, Jason -- 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
