From: Matthew Wilcox <willy@debian.org>
[moved from linux-scsi to linux-pci since this really isn't scsi-related]
On Sun, Nov 09, 2003 at 11:51:36AM -0500, Doug Ledford wrote:
> I can tell you what's going on here. This is a 450NX based
> motherboard. The 450NX chipset from Intel was the first chipset to have
> peer PCI busses. For backwards compatibility, some machine makers
> hacked their PCI BIOS to have a fake bridge device on PCI bus 0 that
> points to the same bus number as the peer bus. This way if the OS
> didn't know about the peer bus registers it would still find the devices
> by scanning behind the bridge.
Ah, thanks Doug. That saved me a few hours of debugging and
head-scratching ;-)
> In this case we are scanning behind this
> fake bridge and then also scanning based upon the peer bus registers in
> the chipset, and as a result we are finding the device twice. In order
> to fix this problem you need to change the peer bus quirk code for the
> 450NX chipset to scan the list of bus 0 devices looking for a bridge
> that has the same config as the peer bus registers and if so delete the
> bridge from the list. That will avoid double scanning and will avoid
> having the PCI code try and configure sub busses via a fake bridge when
> it should do all configurations via the 450NX peer bus registers.
I agree. I considered some other possibilities like having
pci_scan_bridge() check for duplicate busses and return if it detects
them, but that would leave some pcipci bridges in the list that really
don't exist.
Here's a patch that compiles ... comments?
arch/i386/pci/fixup.c | 33 +++++++++++++++++++++++++++++----
1 files changed, 29 insertions(+), 4 deletions(-)
diff -puN arch/i386/pci/fixup.c~i450nx-scanning-fix arch/i386/pci/fixup.c
--- 25/arch/i386/pci/fixup.c~i450nx-scanning-fix 2003-11-09 16:58:55.000000000 -0800
+++ 25-akpm/arch/i386/pci/fixup.c 2003-11-09 16:58:55.000000000 -0800
@@ -6,27 +6,52 @@
#include <linux/init.h>
#include "pci.h"
+static void __devinit i450nx_scan_bus(struct pci_bus *parent, u8 busnr)
+{
+ struct list_head *tmp;
+
+ pci_scan_bus(busnr, &pci_root_ops, NULL);
+
+ list_for_each(tmp, &parent->children) {
+ u8 childnr;
+ struct pci_dev *dev = pci_dev_b(tmp);
+
+ if (dev->hdr_type != PCI_HEADER_TYPE_BRIDGE)
+ continue;
+ pci_read_config_byte(dev, PCI_PRIMARY_BUS, &childnr);
+ if (childnr != busnr)
+ continue;
+
+ printk(KERN_WARNING "PCI: Removing fake PCI bridge %s\n",
+ pci_name(dev));
+ pci_remove_bus_device(dev);
+ break;
+ }
+}
static void __devinit pci_fixup_i450nx(struct pci_dev *d)
{
/*
* i450NX -- Find and scan all secondary buses on all PXB's.
+ * Some manufacturers added fake PCI-PCI bridges that also point
+ * to the peer busses. Look for them and delete them.
*/
int pxb, reg;
u8 busno, suba, subb;
- printk(KERN_WARNING "PCI: Searching for i450NX host bridges on %s\n", pci_name(d));
+ printk(KERN_NOTICE "PCI: Searching for i450NX host bridges on %s\n", pci_name(d));
reg = 0xd0;
- for(pxb=0; pxb<2; pxb++) {
+ for (pxb = 0; pxb < 2; pxb++) {
pci_read_config_byte(d, reg++, &busno);
pci_read_config_byte(d, reg++, &suba);
pci_read_config_byte(d, reg++, &subb);
DBG("i450NX PXB %d: %02x/%02x/%02x\n", pxb, busno, suba, subb);
if (busno)
- pci_scan_bus(busno, &pci_root_ops, NULL); /* Bus A */
+ i450nx_scan_bus(d->bus, busno); /* Bus A */
if (suba < subb)
- pci_scan_bus(suba+1, &pci_root_ops, NULL); /* Bus B */
+ i450nx_scan_bus(d->bus, suba+1); /* Bus B */
}
+
pcibios_last_bus = -1;
}
_