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, 20 insertions, 0 deletions

diff --git a/arch/x86/pci/common.c b/arch/x86/pci/common.c
index 215a27ae050..a0772af64ef 100644
--- a/arch/x86/pci/common.c
+++ b/arch/x86/pci/common.c
@@ -125,6 +125,23 @@ void __init dmi_check_skip_isa_align(void)
 static void __devinit pcibios_fixup_device_resources(struct pci_dev *dev)
 {
         struct resource *rom_r = &dev->resource[PCI_ROM_RESOURCE];
+        struct resource *bar_r;
+        int bar;
+
+        if (pci_probe & PCI_NOASSIGN_BARS) {
+                /*
+                * If the BIOS did not assign the BAR, zero out the
+                * resource so the kernel doesn't attmept to assign
+                * it later on in pci_assign_unassigned_resources
+                */
+                for (bar = 0; bar <= PCI_STD_RESOURCE_END; bar++) {
+                        bar_r = &dev->resource[bar];
+                        if (bar_r->start == 0 && bar_r->end != 0) {
+                                bar_r->flags = 0;
+                                bar_r->end = 0;
+                        }
+                }
+        }
 
         if (pci_probe & PCI_NOASSIGN_ROMS) {
                 if (rom_r->parent)
@@ -509,6 +526,9 @@ char * __devinit  pcibios_setup(char *str)
         } else if (!strcmp(str, "norom")) {
                 pci_probe |= PCI_NOASSIGN_ROMS;
                 return NULL;
+        } else if (!strcmp(str, "nobar")) {
+                pci_probe |= PCI_NOASSIGN_BARS;
+                return NULL;
         } else if (!strcmp(str, "assign-busses")) {
                 pci_probe |= PCI_ASSIGN_ALL_BUSSES;
                 return NULL;