Bjorn Helgaas wrote: > To find a host bridge's downstream bus number, we currently look at _BBN > first. If _BBN returns a bus number we've already seen, we conclude that > _BBN was wrong and look for a bus number in _CRS. > > However, the spec[1] (figure 5-5 and the example in sec 9.12.1) and an ACPI > FAQ[2] suggest that the OS should use _CRS to discover the bus number > range, and that _BBN is really intended to bootstrap _CRS methods that > reference PCI opregions. > > This patch makes us always look at _CRS first. If _CRS doesn't supply a > bus number, we look at _BBN. If _BBN doesn't exist, we default to zero. > This makes the behavior consistent regardless of device discovery order. > Previously, if A and B had duplicate _BBNs and we found A first, we'd only > look at B's _CRS, whereas if we found B first, we'd only look at A's _CRS. > > I'm told that Windows discovers host bridge bus numbers using _CRS, so > it should be fairly safe to rely on this BIOS functionality. > > This patch also removes two misleading messages: we printed the "Wrong _BBN > value, reboot and use option 'pci=noacpi'" message before looking at _CRS, > so we would likely find the bus number in _CRS, the system would work fine, > and the user would be confused. The "PCI _CRS %d overrides _BBN 0" message > incorrectly assumes _BBN was zero, and it's useless anyway because we > print the segment/bus number a few lines later. Though it might be very stupid question, can I ask you a question? Is minimum value of PCI bus number range reported by _CRS always equal to the bus number of the PCI root bus? I glanced over the specs, but I could not confirm it. Thanks, Kenji Kaneshige > > References: > [1] http://www.acpi.info/DOWNLOADS/ACPIspec30b.pdf > [2] http://www.acpi.info/acpi_faq.htm _BBN/_CRS discussion > http://download.microsoft.com/download/9/8/f/98f3fe47-dfc3-4e74-92a3-088782200fe7/TWAR05005_WinHEC05.ppt (slide 17) > http://bugzilla.kernel.org/show_bug.cgi?id=1662 ASUS PR-DLS > http://bugzilla.kernel.org/show_bug.cgi?id=1127 ASUS PR-DLSW > http://bugzilla.kernel.org/show_bug.cgi?id=1741 ASUS PR-DLS533 > > Signed-off-by: Bjorn Helgaas <bjorn.helgaas@xxxxxx> > Reviewed-by: Alex Chiang <achiang@xxxxxx> > CC: Shaohua Li <shaohua.li@xxxxxxxxx> > CC: Kenji Kaneshige <kaneshige.kenji@xxxxxxxxxxxxxx> > --- > drivers/acpi/pci_root.c | 54 ++++++++++++++--------------------------------- > 1 files changed, 16 insertions(+), 38 deletions(-) > > diff --git a/drivers/acpi/pci_root.c b/drivers/acpi/pci_root.c > index f341b07..7847732 100644 > --- a/drivers/acpi/pci_root.c > +++ b/drivers/acpi/pci_root.c > @@ -470,12 +470,12 @@ static int __devinit acpi_pci_root_add(struct acpi_device *device) > { > int result = 0; > struct acpi_pci_root *root = NULL; > - struct acpi_pci_root *tmp; > acpi_status status = AE_OK; > unsigned long long value = 0; > acpi_handle handle = NULL; > struct acpi_device *child; > u32 flags, base_flags; > + int bus; > > > if (!device) > @@ -523,46 +523,24 @@ static int __devinit acpi_pci_root_add(struct acpi_device *device) > /* > * Bus > * --- > - * Obtained via _BBN, if exists, otherwise assumed to be zero (0). > + * Check _CRS first, then _BBN. If no _BBN, default to zero. > */ > - status = acpi_evaluate_integer(device->handle, METHOD_NAME__BBN, NULL, > - &value); > - switch (status) { > - case AE_OK: > - root->id.bus = (u16) value; > - break; > - case AE_NOT_FOUND: > - ACPI_DEBUG_PRINT((ACPI_DB_INFO, "Assuming bus 0 (no _BBN)\n")); > - root->id.bus = 0; > - break; > - default: > - ACPI_EXCEPTION((AE_INFO, status, "Evaluating _BBN")); > - result = -ENODEV; > - goto end; > - } > - > - /* Some systems have wrong _BBN */ > - list_for_each_entry(tmp, &acpi_pci_roots, node) { > - if ((tmp->id.segment == root->id.segment) > - && (tmp->id.bus == root->id.bus)) { > - int bus = 0; > - acpi_status status; > - > - printk(KERN_ERR PREFIX > - "Wrong _BBN value, reboot" > - " and use option 'pci=noacpi'\n"); > - > - status = try_get_root_bridge_busnr(device->handle, &bus); > - if (ACPI_FAILURE(status)) > - break; > - if (bus != root->id.bus) { > - printk(KERN_INFO PREFIX > - "PCI _CRS %d overrides _BBN 0\n", bus); > - root->id.bus = bus; > - } > - break; > + status = try_get_root_bridge_busnr(device->handle, &bus); > + if (ACPI_SUCCESS(status)) > + root->id.bus = bus; > + else { > + status = acpi_evaluate_integer(device->handle, METHOD_NAME__BBN, NULL, &value); > + if (ACPI_SUCCESS(status)) > + root->id.bus = (u16) value; > + else if (status == AE_NOT_FOUND) > + root->id.bus = 0; > + else { > + ACPI_EXCEPTION((AE_INFO, status, "Evaluating _BBN")); > + result = -ENODEV; > + goto end; > } > } > + > /* > * Device & Function > * ----------------- > > > -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
