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

[Stefan Bader]

Yingying Zhao wrote:
> 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.
> 

Thanks Yingying,

it seems that I was looking for that patch without knowing that I was looking 
for that. ;-) This https://bugs.launchpad.net/ubuntu/+source/linux/+bug/267295 
report really sounds like the exact problem that is described, so I'll use that 
for the SRU.

Stefan

> 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;
> +		}
>  }
> 
> 
> 


-- 

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