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Date:   Thu, 14 Jul 2022 05:56:13 +0100
From:   Matthew Garrett <mjg59@srcf.ucam.org>
To:     Kai-Heng Feng <kai.heng.feng@canonical.com>
Cc:     Bjorn Helgaas <helgaas@kernel.org>,
        Manyi Li <limanyi@uniontech.com>, bhelgaas@google.com,
        refactormyself@gmail.com, kw@linux.com, rajatja@google.com,
        linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org,
        Vidya Sagar <vidyas@nvidia.com>
Subject: Re: [PATCH] PCI/ASPM: Should not report ASPM support to BIOS if FADT
 indicates ASPM is unsupported
Message-ID: <20220714045613.GA8720@srcf.ucam.org>
References: <20220713112612.6935-1-limanyi@uniontech.com>
 <20220713182852.GA841582@bhelgaas>
 <CAAd53p7g2Md73=UU6Rp-TZkksc+H02KAX58bWCzsgQ__VwvJ+g@mail.gmail.com>
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On Thu, Jul 14, 2022 at 11:20:26AM +0800, Kai-Heng Feng wrote:

> According to commit 387d37577fdd ("PCI: Don't clear ASPM bits when the
> FADT declares it's unsupported"), the bit means "just use the ASPM

Yes, the assumption is that if the BIOS set up ASPM but FADT indicates 
it's unsupported, just trust that the BIOS did the right thing and don't 
interfere. It's been a long time, but when we were clearing the ASPM 
bits in response to this FADT setting, a bunch of machines suddenly 
started consuming a lot more power than when running Windows.