netdev - Re: [PATCH] pciaer: report config read/write errors

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Date:	Tue, 2 Dec 2008 13:41:55 -0800
From:	Stephen Hemminger <shemminger@...tta.com>
To:	Loic Prylli <loic@...i.com>
Cc:	David Miller <davem@...emloft.net>, jeffrey.t.kirsher@...el.com,
	netdev@...r.kernel.org, jeff@...zik.org,
	peter.p.waskiewicz.jr@...el.com, linux-pci@...r.kernel.org
Subject: Re: [PATCH] pciaer: report config read/write errors

On Tue, 02 Dec 2008 15:14:35 -0500
Loic Prylli <loic@...i.com> wrote:

> On 12/02/2008 02:44 PM, Stephen Hemminger wrote:
> > pci_find_ext_capability would succeed but all access to registers >= 256
> > would fail if MMCONFIG failed. 
> 
> 
> 
> Your sentence seems self-contradicting to me. pci_find_ext_capability() 
> (!=  pci_find_capability()) only tries to access registers >= 256, so I 
> don't see how it would succeed if *all* those accesses are failing.
> 
> 
> > P.s: you can look back into LKML for Linus discussion about why MMCONFIG
> > is broken anyway.
> >   
> 
> 
> 
> I was an active participant in one of those discussions (although it is 
> possible I missed a later one), so I am quite aware about the 
> limitations of MMCONFIG. But pci_find_ext_capability() looked to me a 
> good filter to check about those limitations().
> 
> This is not just about pciaer, for instance, it might be that a lot of 
> the SR-IOV code submitted recently assumes that if the corresponding 
> extended-capability can be detected, little checking needs to be done 
> afterwards.

I misremembered the issue.
The problem in sky2 was related but not the same. pci_find_ext_capability
would return 0, but the device driver needed to be able to clear errors
(or IRQ would scream). So since the existing extended capability code
wouldn't work on all platforms, another alternative had to be found.
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