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@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
* -----------------
--
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