[PATCH] [Intrepid SRU, Jaunty] x86: only scan the root bus in early PCI quirks

[Yingying Zhao]

SRU Justification:
We found a problem that on Tylersburg-HEDT with Nvidia Graphics card, system may result in kernel panic. Andi Kleen provided the patch to fix this problem. Please consider to include this patch in Jaunty and Intrepid.

Patch (also attached):
--
commit 8659c406ade32f47da2c95889094801921d6330a
Author: Andi Kleen <andi at firstfloor.org>
Date:   Fri Jan 9 12:17:39 2009 -0800

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

diff --git a/arch/x86/kernel/early-quirks.c b/arch/x86/kernel/early-quirks.c
index 744aa7f..76b8cd9 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;
+		}
 }


-- 
Yingying Zhao
Intel Open Source Technology Center
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