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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 <bjorn.helgaas@hp.com> Reviewed-by: Alex Chiang <achiang@hp.com> CC: Shaohua Li <shaohua.li@intel.com> CC: Kenji Kaneshige <kaneshige.kenji@jp.fujitsu.com> Signed-off-by: Len Brown <len.brown@intel.com>
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1 changed files with 16 additions and 38 deletions
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@ -365,12 +365,12 @@ static int __devinit acpi_pci_root_add(struct acpi_device *device)
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{
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int result = 0;
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struct acpi_pci_root *root = NULL;
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struct acpi_pci_root *tmp;
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acpi_status status = AE_OK;
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unsigned long long value = 0;
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acpi_handle handle = NULL;
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struct acpi_device *child;
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u32 flags, base_flags;
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int bus;
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if (!device)
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@ -420,46 +420,24 @@ static int __devinit acpi_pci_root_add(struct acpi_device *device)
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/*
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* Bus
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* ---
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* Obtained via _BBN, if exists, otherwise assumed to be zero (0).
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* Check _CRS first, then _BBN. If no _BBN, default to zero.
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*/
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status = acpi_evaluate_integer(device->handle, METHOD_NAME__BBN, NULL,
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&value);
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switch (status) {
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case AE_OK:
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root->id.bus = (u16) value;
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break;
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case AE_NOT_FOUND:
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ACPI_DEBUG_PRINT((ACPI_DB_INFO, "Assuming bus 0 (no _BBN)\n"));
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root->id.bus = 0;
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break;
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default:
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ACPI_EXCEPTION((AE_INFO, status, "Evaluating _BBN"));
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result = -ENODEV;
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goto end;
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}
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/* Some systems have wrong _BBN */
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list_for_each_entry(tmp, &acpi_pci_roots, node) {
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if ((tmp->id.segment == root->id.segment)
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&& (tmp->id.bus == root->id.bus)) {
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int bus = 0;
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acpi_status status;
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printk(KERN_ERR PREFIX
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"Wrong _BBN value, reboot"
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" and use option 'pci=noacpi'\n");
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status = try_get_root_bridge_busnr(device->handle, &bus);
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if (ACPI_FAILURE(status))
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break;
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if (bus != root->id.bus) {
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printk(KERN_INFO PREFIX
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"PCI _CRS %d overrides _BBN 0\n", bus);
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root->id.bus = bus;
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}
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break;
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status = try_get_root_bridge_busnr(device->handle, &bus);
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if (ACPI_SUCCESS(status))
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root->id.bus = bus;
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else {
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status = acpi_evaluate_integer(device->handle, METHOD_NAME__BBN, NULL, &value);
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if (ACPI_SUCCESS(status))
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root->id.bus = (u16) value;
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else if (status == AE_NOT_FOUND)
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root->id.bus = 0;
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else {
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ACPI_EXCEPTION((AE_INFO, status, "Evaluating _BBN"));
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result = -ENODEV;
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goto end;
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}
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}
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/*
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* Device & Function
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* -----------------
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