linux-kernel - Re: [PATCH] PCI/ASPM: Should not report ASPM support to BIOS if FADT indicates ASPM is unsupported

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Date:   Fri, 15 Jul 2022 09:29:45 +0100
From:   Matthew Garrett <mjg59@...f.ucam.org>
To:     Manyi Li <limanyi@...ontech.com>
Cc:     Kai-Heng Feng <kai.heng.feng@...onical.com>,
        Bjorn Helgaas <helgaas@...nel.org>, bhelgaas@...gle.com,
        refactormyself@...il.com, kw@...ux.com, rajatja@...gle.com,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        Vidya Sagar <vidyas@...dia.com>, rafael@...nel.org
Subject: Re: [PATCH] PCI/ASPM: Should not report ASPM support to BIOS if FADT
 indicates ASPM is unsupported

On Fri, Jul 15, 2022 at 03:40:36PM +0800, Manyi Li wrote:

> Please see the details of this issus:
> https://bugzilla.kernel.org/show_bug.cgi?id=216245

Hmm. The only case where changing aspm_support_enabled to false should 
matter is in pcie_aspm_init_link_state(), where it looks like we'll 
potentially rewrite some registers even if aspm_disabled is true. I 
think in theory we shouldn't actually modify anything as a result, and 
the lspcis from the bug don't show any ASPM values having changed, but I 
don't trust Realtek hardware in the general case so maybe it gets upset 
here? If the proposed patch is to just set aspm_support_enabled to false 
when we see the FADT bit set then I think this is fine.