From fbe2b31b4b6dfa790cbc88e00631f3112c4fc54e Mon Sep 17 00:00:00 2001 From: Bjorn Helgaas Date: Thu, 18 Jun 2009 14:46:47 -0600 Subject: ACPI: pci_root: check _CRS, then _BBN for downstream bus number 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. 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 Reviewed-by: Alex Chiang CC: Shaohua Li CC: Kenji Kaneshige Signed-off-by: Len Brown --- drivers/acpi/pci_root.c | 54 +++++++++++++++---------------------------------- 1 file changed, 16 insertions(+), 38 deletions(-) (limited to 'drivers/acpi') diff --git a/drivers/acpi/pci_root.c b/drivers/acpi/pci_root.c index 196f97d0095..a8b25078393 100644 --- a/drivers/acpi/pci_root.c +++ b/drivers/acpi/pci_root.c @@ -365,12 +365,12 @@ 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) @@ -420,46 +420,24 @@ 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 * ----------------- -- cgit v1.2.3