x86/PCI: use host bridge _CRS info by default on 2008 and newer machines

The main benefit of using ACPI host bridge window information is that
we can do better resource allocation in systems with multiple host bridges,
e.g., http://bugzilla.kernel.org/show_bug.cgi?id=14183

Sometimes we need _CRS information even if we only have one host bridge,
e.g., https://bugs.launchpad.net/ubuntu/+source/linux/+bug/341681

Most of these systems are relatively new, so this patch turns on
"pci=use_crs" only on machines with a BIOS date of 2008 or newer.

Signed-off-by: Bjorn Helgaas <bjorn.helgaas@hp.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>

1 files changed, 6 insertions, 2 deletions

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 516225a864f9..3e69c1c4f508 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -1948,8 +1948,12 @@ and is between 256 and 4096 characters. It is defined in the file
                                 IRQ routing is enabled.
                 noacpi          [X86] Do not use ACPI for IRQ routing
                                 or for PCI scanning.
-                use_crs         [X86] Use _CRS for PCI resource
-                                allocation.
+                use_crs         [X86] Use PCI host bridge window information
+                                from ACPI.  On BIOSes from 2008 or later, this
+                                is enabled by default.  If you need to use this,
+                                please report a bug.
+                nocrs           [X86] Ignore PCI host bridge windows from ACPI.
+                                If you need to use this, please report a bug.
                 routeirq        Do IRQ routing for all PCI devices.
                                 This is normally done in pci_enable_device(),
                                 so this option is a temporary workaround