x86/PCI: Add option to not assign BAR's if not already assigned

The Linux kernel assigns BARs that a BIOS did not assign, most likely
to handle broken BIOSes that didn't enumerate the devices correctly.
On UV the BIOS purposely doesn't assign I/O BARs for certain devices/
drivers we know don't use them (examples, LSI SAS, Qlogic FC, ...).
We purposely don't assign these I/O BARs because I/O Space is a very
limited resource.  There is only 64k of I/O Space, and in a PCIe
topology that space gets divided up into 4k chucks (this is due to
the fact that a pci-to-pci bridge's I/O decoder is aligned at 4k)...
Thus a system can have at most 16 cards with I/O BARs: (64k / 4k = 16)

SGI needs to scale to >16 devices with I/O BARs.  So by not assigning
I/O BARs on devices we know don't use them, we can do that (iff the
kernel doesn't go and assign these BARs that the BIOS purposely didn't
assign).

This patch will not assign a resource to a device BAR if that BAR was
not assigned by the BIOS, and the kernel cmdline option 'pci=nobar'
was specified.   This patch is closely modeled after the 'pci=norom'
option that currently exists in the tree.

Signed-off-by: Mike Habeck <habeck@sgi.com>
Signed-off-by: Mike Travis <travis@sgi.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>

1 files changed, 2 insertions, 0 deletions

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 2b2407d9a6d0..4fac69beeb4f 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -1970,6 +1970,8 @@ and is between 256 and 4096 characters. It is defined in the file
 		norom		[X86] Do not assign address space to
 				expansion ROMs that do not already have
 				BIOS assigned address ranges.
+		nobar		[X86] Do not assign address space to the
+				BARs that weren't assigned by the BIOS.
 		irqmask=0xMMMM	[X86] Set a bit mask of IRQs allowed to be
 				assigned automatically to PCI devices. You can
 				make the kernel exclude IRQs of your ISA cards