linux-kernel - Re: [PATCH] PCI: Remove not needed check in disable aspm link

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Date:	Fri, 29 Mar 2013 20:11:31 +0200
From:	Roman Yepishev <roman.yepishev@...il.com>
To:	Bjorn Helgaas <bhelgaas@...gle.com>
Cc:	Yinghai Lu <yinghai@...nel.org>, "Rafael J. Wysocki" <rjw@...k.pl>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Taku Izumi <izumi.taku@...fujitsu.com>,
	Kenji Kaneshige <kaneshige.kenji@...fujitsu.com>,
	Matthew Garrett <matthew.garrett@...ula.com>,
	e1000-devel@...ts.sourceforge.net
Subject: Re: [PATCH] PCI: Remove not needed check in disable aspm link

On Fri, Mar 29, 2013 at 5:22 AM, Bjorn Helgaas <bhelgaas@...gle.com> wrote:
> [+cc Matthew]
> [+cc e1000-devel@...ts.sourceforge.net for suspected 82575/82598 regression]
>
> I think this regression has nothing to do with pci_disable_link_state().
>
> ...
>
> There are also PCI_FIXUP_FINAL quirks for 82575 and 82598 NICs that call
> pci_disable_link_state().  In 3.7, these quirks are run before
> aspm_disabled is set, but 8c33f51d moved the pcie_no_aspm() call up
> before we start scanning the bus, so in 3.8, aspm_disabled is set
> *before* we run them.  I think that means 8c33f51d broke all these
> quirks.  That's also a problem, of course, but this isn't the one Roman
> is seeing either.
I have to say that my iwlwifi device (Intel Corporation Centrino
Wireless-N 1000 [Condor Peak] [8086:0084] also appears to be affected
- it calls pci_disable_link_state too and in current 3.8 that does not
do anything. It looks like it affects something when the system is
resumed from suspend, but I was not able to confirm that yet (but
there's a thread about removing the code since it did not appear to
work - http://thread.gmane.org/gmane.linux.kernel.pci/20628/focus=20640)

> I think the problem Roman is seeing happens when
> pcie_aspm_init_link_state() calls pcie_aspm_sanity_check() during device
> enumeration.  In 3.8, the fact that aspm_disabled is already set by the
> time we get here means we skip the check for pre-1.1 PCIe devices, and
> I think *this* is what Roman is seeing.
>
> I suspect the following hunk of your patch is enough to fix things for
> Roman:
>
>> --- linux-2.6.orig/drivers/pci/pcie/aspm.c
>> +++ linux-2.6/drivers/pci/pcie/aspm.c
>> @@ -493,15 +492,6 @@ static int pcie_aspm_sanity_check(struct
>>                       return -EINVAL;
>>
>>               /*
>> -              * If ASPM is disabled then we're not going to change
>> -              * the BIOS state. It's safe to continue even if it's a
>> -              * pre-1.1 device
>> -              */
>> -
>> -             if (aspm_disabled)
>> -                     continue;
>> -
>> -             /*
>>                * Disable ASPM for pre-1.1 PCIe device, we follow MS to use
>>                * RBER bit to determine if a function is 1.1 version device
>>                */
>
> However, this test was added by Matthew in c9651e70, and I can't remove
> it unless we have an explanation of why removing it will not reintroduce
> the bug he was fixing.
>
> This code is such a terrible mess that it's not surprising at all that
> we have all these issues.  But there's too much to untangle in v3.9; all
> we can hope for is to fix the regressions in v3.9 and clean it up later.
>
I have removed the check and indeed it allowed ASPM to become disabled
during the ath5k driver load.

--
Regards, Roman Yepishev
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