x86: only scan the root bus in early PCI quirks

We found a situation on Linus' machine that the Nvidia timer quirk hit on
a Intel chipset system.  The problem is that the system has a fancy Nvidia
card with an own PCI bridge, and the early-quirks code looking for any
NVidia bridge triggered on it incorrectly.  This didn't lead a boot
failure by luck, but the timer routing code selecting the wrong timer
first and some ugly messages.  It might lead to real problems on other
systems.

I checked all the devices which are currently checked for by early_quirks
and it turns out they are all located in the root bus zero.

So change the early-quirks loop to only scan bus 0.  This incidently also
saves quite some unnecessary scanning work, because early_quirks doesn't
go through all the non root busses.

The graphics card is not on bus 0, so it is not matched anymore.

Signed-off-by: Andi Kleen <ak@linux.intel.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 14 insertions, 8 deletions

diff --git a/arch/x86/kernel/early-quirks.c b/arch/x86/kernel/early-quirks.c
index 744aa7fc49d..76b8cd953de 100644
--- a/arch/x86/kernel/early-quirks.c
+++ b/arch/x86/kernel/early-quirks.c
@@ -201,6 +201,12 @@ struct chipset {
         void (*f)(int num, int slot, int func);
 };
 
+/*
+ * Only works for devices on the root bus. If you add any devices
+ * not on bus 0 readd another loop level in early_quirks(). But
+ * be careful because at least the Nvidia quirk here relies on
+ * only matching on bus 0.
+ */
 static struct chipset early_qrk[] __initdata = {
         { PCI_VENDOR_ID_NVIDIA, PCI_ANY_ID,
           PCI_CLASS_BRIDGE_PCI, PCI_ANY_ID, QFLAG_APPLY_ONCE, nvidia_bugs },
@@ -267,17 +273,17 @@ static int __init check_dev_quirk(int num, int slot, int func)
 
 void __init early_quirks(void)
 {
-        int num, slot, func;
+        int slot, func;
 
         if (!early_pci_allowed())
                 return;
 
         /* Poor man's PCI discovery */
-        for (num = 0; num < 32; num++)
-                for (slot = 0; slot < 32; slot++)
-                        for (func = 0; func < 8; func++) {
-                                /* Only probe function 0 on single fn devices */
-                                if (check_dev_quirk(num, slot, func))
-                                        break;
-                        }
+        /* Only scan the root bus */
+        for (slot = 0; slot < 32; slot++)
+                for (func = 0; func < 8; func++) {
+                        /* Only probe function 0 on single fn devices */
+                        if (check_dev_quirk(0, slot, func))
+                                break;
+                }
 }