| Message ID | 20120709203203.28178.15800.stgit@bhelgaas.mtv.corp.google.com |
|---|---|
| State | Accepted |
| Headers | show |
On Mon, Jul 9, 2012 at 1:32 PM, Bjorn Helgaas <bhelgaas@google.com> wrote: > cd81e1ea1a4c added checks that prevent us from using P2P bridge windows > that start at PCI bus address zero. The reason was to "prevent us from > overwriting resources that are unassigned." > > But generic code should allow address zero in both BARs and bridge > windows, so I think that commit was a mistake. > > Windows at bus address zero are legal and likely to exist on machines with > an offset between bus addresses and CPU addresses. For example, in the > following hypothetical scenario, the bridge at 00:01.0 has a window at bus > address zero and the device at 01:00.0 has a BAR at bus address zero, and > I think both are perfectly valid: > > PCI host bridge to bus 0000:00 > pci_bus 0000:00: root bus resource [mem 0x100000000-0x1ffffffff] (bus address [0x00000000-0xffffffff]) > pci 0000:00:01.0: PCI bridge to [bus 01] > pci 0000:00:01.0: bridge window [mem 0x100000000-0x100ffffff] > pci 0000:01:00.0: reg 10: [mem 0x100000000-0x100ffffff] > > CC: Yinghai Lu <yinghai@kernel.org> > Signed-off-by: Bjorn Helgaas <bhelgaas@google.com> Acked-by: Yinghai Lu <yinghai@kernel.org> -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c index 658ac97..9c5d2a9 100644 --- a/drivers/pci/probe.c +++ b/drivers/pci/probe.c @@ -287,7 +287,7 @@ static void __devinit pci_read_bridge_io(struct pci_bus *child) limit |= (io_limit_hi << 16); } - if (base && base <= limit) { + if (base <= limit) { res->flags = (io_base_lo & PCI_IO_RANGE_TYPE_MASK) | IORESOURCE_IO; res2.flags = res->flags; region.start = base; @@ -314,7 +314,7 @@ static void __devinit pci_read_bridge_mmio(struct pci_bus *child) pci_read_config_word(dev, PCI_MEMORY_LIMIT, &mem_limit_lo); base = (mem_base_lo & PCI_MEMORY_RANGE_MASK) << 16; limit = (mem_limit_lo & PCI_MEMORY_RANGE_MASK) << 16; - if (base && base <= limit) { + if (base <= limit) { res->flags = (mem_base_lo & PCI_MEMORY_RANGE_TYPE_MASK) | IORESOURCE_MEM; region.start = base; region.end = limit + 0xfffff; @@ -360,7 +360,7 @@ static void __devinit pci_read_bridge_mmio_pref(struct pci_bus *child) #endif } } - if (base && base <= limit) { + if (base <= limit) { res->flags = (mem_base_lo & PCI_PREF_RANGE_TYPE_MASK) | IORESOURCE_MEM | IORESOURCE_PREFETCH; if (res->flags & PCI_PREF_RANGE_TYPE_64)
cd81e1ea1a4c added checks that prevent us from using P2P bridge windows that start at PCI bus address zero. The reason was to "prevent us from overwriting resources that are unassigned." But generic code should allow address zero in both BARs and bridge windows, so I think that commit was a mistake. Windows at bus address zero are legal and likely to exist on machines with an offset between bus addresses and CPU addresses. For example, in the following hypothetical scenario, the bridge at 00:01.0 has a window at bus address zero and the device at 01:00.0 has a BAR at bus address zero, and I think both are perfectly valid: PCI host bridge to bus 0000:00 pci_bus 0000:00: root bus resource [mem 0x100000000-0x1ffffffff] (bus address [0x00000000-0xffffffff]) pci 0000:00:01.0: PCI bridge to [bus 01] pci 0000:00:01.0: bridge window [mem 0x100000000-0x100ffffff] pci 0000:01:00.0: reg 10: [mem 0x100000000-0x100ffffff] CC: Yinghai Lu <yinghai@kernel.org> Signed-off-by: Bjorn Helgaas <bhelgaas@google.com> --- drivers/pci/probe.c | 6 +++--- 1 files changed, 3 insertions(+), 3 deletions(-) -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html