linux-kernel - Re: [PATCH] x86/pci: try to detect host_bridge pci_cfg

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Date:	Fri, 06 Mar 2009 17:04:27 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Yinghai Lu <yinghai@...nel.org>
CC:	Jesse Barnes <jbarnes@...tuousgeek.org>,
	Matthew Wilcox <matthew@....cx>, Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-pci@...r.kernel.org
Subject: Re: [PATCH] x86/pci: try to detect host_bridge pci_cfg_space

H. Peter Anvin wrote:
> Yinghai Lu wrote:
>> Impact: get correct pci_cfg_size for host_bridge
>>
>> more host bridges support 4k cfg, so check them directly
>> instead of quirks.
>>
>> Signed-off-by: Yinghai Lu <yinghai@...nel.org>
> 
> I'm utterly confused by this.  This is basically saying we should try to 
> probe for an extended device space for every host bridge.  Logically 
> speaking, this is valid: if there is a valid path by which we can probe 
> for byte 256 then it should succeed.
> 
> HOWEVER, the same argument applies for *every single device*.  So if 
> this does indeed work, why should we limit it to host bridges?
> 

Looking at the code (as opposed to just the patch) made it a bit 
clearer.  The argument you're making here is that only host bridges are 
known to have extended address space without also having a PCI-X 
extension header, right?

	-hpa

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