linux-kernel - Re: [PATCH] x86, pci: Fix all early PCI scans to check the vendor ID first

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Date:	Sun, 12 Aug 2012 21:23:01 -0600
From:	Khalid Aziz <khalid.aziz@...com>
To:	"H. Peter Anvin" <hpa@...or.com>
CC:	Betty Dall <betty.dall@...com>, Andi Kleen <andi@...stfloor.org>,
	x86@...nel.org, linux-kernel@...r.kernel.org,
	Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH] x86, pci: Fix all early PCI scans to check the vendor
 ID first

On 08/10/2012 05:57 PM, H. Peter Anvin wrote:
> On 08/09/2012 03:34 PM, Betty Dall wrote:
>> I thought this should be a break instead of a continue since the code
>> does a break if the class is 0xffffffff. If the function does not have a
>> valid VENDOR_ID, then the remaining function numbers do not have to be
>> scanned because functions are required to be implemented in order (no
>> skipping a function number.)
>>
> Is that true?  This is certainly not true in PCI in general: there is
> required to be a function 0, but there is no guarantee that functions
> 1-7 don't have gaps.

If that is the case, there is a problem in the original code in
arch/x86/kernel/aperture_64.c.The original code already stops scanning
functions the first time it finds an invalid PCI class:

206                         for (func = 0; func < 8; func++) {
207                                 u32 class, cap;
208                                 u8 type;
209                                 class = read_pci_config(bus, slot, func,
210 PCI_CLASS_REVISION);
211                                 if (class == 0xffffffff)
212                                         break;

-- 
====================================================================
Khalid Aziz
khalid.aziz@...com

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