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Subject: Re: Lost PCIe PME after a914ff2d78ce ("PCI/ASPM: Don't select
 CONFIG_PCIEASPM by default")
To:     Matthew Garrett <mjg59@srcf.ucam.org>,
        Bjorn Helgaas <helgaas@kernel.org>
Cc:     "Rafael J. Wysocki" <rjw@rjwysocki.net>,
        Bjorn Helgaas <bhelgaas@google.com>,
        "linux-pci@vger.kernel.org" <linux-pci@vger.kernel.org>,
        linux-kernel@vger.kernel.org, linux-acpi@vger.kernel.org
References: <bdc33be8-1db6-b147-cbc4-90fa0dc3d999@gmail.com>
 <20200529202135.GA461617@bjorn-Precision-5520>
 <20200529205900.whx3mxuvt6ijlqwg@srcf.ucam.org>
From:   Heiner Kallweit <hkallweit1@gmail.com>
Message-ID: <824d63d8-668c-22c8-a303-b44e30e805e1@gmail.com>
Date:   Sat, 30 May 2020 00:26:17 +0200
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On 29.05.2020 22:59, Matthew Garrett wrote:
> On Fri, May 29, 2020 at 03:21:35PM -0500, Bjorn Helgaas wrote:
> 
>> Yeah, that makes sense.  I can't remember the details, but I'm pretty
>> sure there's a reason why we ask for the whole set of things.  Seems
>> like it solved some problem.  I think Matthew Garrett might have been
>> involved in that.
> 
> This was https://bugzilla.redhat.com/show_bug.cgi?id=638912 - some 
> firmware misbehaves unless you pass the same set of supported 
> functionality as Windows does.
> 

Current situation means that PME is unusable on all systems where
pcie_aspm_support_enabled() returns false, what is basically every
system except EXPERT mode is enabled and CONFIG_PCIEASPM is set.
So we definitely need to do something.

One question is whether the system from the 10yr old bug report
actually depends on OSC_PCI_EXPRESS_LTR_CONTROL control, or whether
some other change in recent years fixed the issue.
Not sure whether the system is still available for re-testing.

If worst case we have 10yr old systems breaking with a new kernel
then we still would have the workaround to enable CONFIG_PCIEASPM
on that system.