linux-kernel - Re: ASM1083 PCIx-PCI bridge interrupts

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Date:	Mon, 30 Jan 2012 20:12:56 -0600
From:	Robert Hancock <hancockrwd@...il.com>
To:	Chris Palmer <chris.palmer@...ox.com>
CC:	torvalds@...ux-foundation.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Len Brown <lenb@...nel.org>, ghost3k@...st3k.net,
	linux-kernel@...r.kernel.org, edward.donovan@...ble.net,
	keve@....hu
Subject: Re: ASM1083 PCIx-PCI bridge interrupts - widespread problems

On 01/30/2012 09:04 AM, Chris Palmer wrote:
> Linus et al
>
>
> For about 6 months many users have been having interrupt problems with PCI boards, but it hasn't been
> easy trying to find where the problem may be. However, it is now looking likely that the problem lies
> in the ASM1083 PCIe-PCI bridge chipset, as used by Asus in many Sandybridge and AMD boards.
>
> My original bug report is:
>      https://bugzilla.kernel.org/show_bug.cgi?id=38632  (Sandybridge)
>
> and there several other similar ones. However there is also extensive investigation in the following thread:
>      http://www.gossamer-threads.com/lists/linux/kernel/1466185  (AMD)
>
> There have also been reports of Windows users having similar problems.
>
> This problem prevents use of PCI boards in any motherboard with that bridge chipset - including most
> ASUS boards. At the moment though we don't know whether the chipset or drivers are faulty, and if a
> workaround is possible.
>
> At the moment my bug is assigned to drivers_network, but this doesn't look appropriate.
>
> Hoping someone can help...

If the analysis posted in the "Unhandled IRQs on AMD E-450" thread is 
correct, then it sounds like the bridge chip is delaying PCIe INTx 
deassert messages. In that case there isn't much the kernel is likely to 
be able to fix it properly, at least not without input from ASMedia or 
someone else with detailed knowledge of the chip.

The workaround posted in that thread (switching to IRQ polling mode on 
the interrupt for some period of time after a screaming IRQ is detected) 
might be a workaround, but definitely would be considered a hack.

Do you have a source/link for people having issues with this on Windows? 
I wouldn't be surprised though - I doubt Windows has any special 
handling for unhandled IRQs so likely it just hammers the IRQ handler 
until the IRQ gets deasserted. In that case the only thing a user might 
notice would be poor performance whenever the devices behind that bridge 
raise interrupts.

>
>
>
>
> On 09/09/2011 00:51, Andrew Morton wrote:
>
>> On Thu, 08 Sep 2011 12:28:40 +0100
>> Chris Palmer<chris.palmer@...ox.com>  wrote:
>>
>>> Andrew
>>>
>>> I'm writing to ask if you could cast a quick eye over the following
>>> bugs, to give an opinion on where they should be assigned. Mine has been
>>> reassigned to Network Drivers but I'm not convinced that is right, and I
>>> think the problem is wider than that.
>>>
>>> In summary, interrupt handling for *PCI boards with ASUS Sandybridge
>>> motherboards* seems to be broken.
>>>
>>> It has been seen with network and non-network PCI boards. PCIx network
>>> boards work OK. And all reports are for ASUS motherboards.
>>>
>>> My bug report is
>>>
>>> https://bugzilla.kernel.org/show_bug.cgi?id=38632
>>>
>>> Others that I know of are:
>>>
>>> https://bugzilla.redhat.com/show_bug.cgi?id=713351
>>> https://bugzilla.kernel.org/show_bug.cgi?id=35332
>>> https://bugzilla.kernel.org/show_bug.cgi?id=34242
>>> https://bugzilla.kernel.org/show_bug.cgi?id=32242
>>> https://bugzilla.kernel.org/show_bug.cgi?id=39122
>>>
>>>
>>> I'm now on kernel 3.0.4 with the problem still there. The only thing
>>> that seems to make a difference is acpi=off (although one person
>>> reported that it merely changed it from minutes to days before occurring).
>>>
>>> I'd appreciate anything you could do to move this in the right direction...
>>>
>>
>> Most likely ACPI, I expect.  I think that's
>> acpi-config-interrupts@...zilla.kernel.org.  kernel.org DNS is dead at
>> present and I can't check.
>>
>> Len, can you suggest how to triage these please?

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