linux-kernel - [PATCH] [1/5] Only scan the root bus in early PCI quirks.

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Message-Id: <20090104233638.60AF53E6653@basil.firstfloor.org>
Date:	Mon,  5 Jan 2009 00:36:38 +0100 (CET)
From:	Andi Kleen <andi@...stfloor.org>
To:	akpm@...ux-foundation.org, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH] [1/5] 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@...ux.intel.com>

---
 arch/x86/kernel/early-quirks.c |   22 ++++++++++++++--------
 1 file changed, 14 insertions(+), 8 deletions(-)

Index: linux-2.6.28-test/arch/x86/kernel/early-quirks.c
===================================================================
--- linux-2.6.28-test.orig/arch/x86/kernel/early-quirks.c	2008-11-24 16:42:46.000000000 +0100
+++ linux-2.6.28-test/arch/x86/kernel/early-quirks.c	2008-12-29 05:25:09.000000000 +0100
@@ -200,6 +200,12 @@
 	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 },
@@ -266,17 +272,17 @@
 
 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;
+		}
 }
--
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