linux-kernel - Re: [PATCH v2 3/3] PCI/ASPM: Add LTR sysfs attributes

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Date:   Thu, 28 Oct 2021 13:16:31 +0800
From:   Kai-Heng Feng <kai.heng.feng@...onical.com>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     Bjorn Helgaas <bhelgaas@...gle.com>,
        Heiner Kallweit <hkallweit1@...il.com>,
        Anthony Wong <anthony.wong@...onical.com>,
        Linux PCI <linux-pci@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Krzysztof Wilczyński <kw@...ux.com>,
        Vidya Sagar <vidyas@...dia.com>,
        Logan Gunthorpe <logang@...tatee.com>
Subject: Re: [PATCH v2 3/3] PCI/ASPM: Add LTR sysfs attributes

On Wed, Oct 27, 2021 at 12:53 AM Bjorn Helgaas <helgaas@...nel.org> wrote:
>
> On Tue, Oct 26, 2021 at 10:28:38AM +0800, Kai-Heng Feng wrote:
>
> > What if we fallback to the original approach and use the VMD driver
> > to enable ASPM and LTR values?  At least I think Intel should be
> > able to provide correct values for their SoC.
>
> Can you post the patches for that?  I'm not sure exactly what the
> original approach was.  Are these the same as the downstream support
> you mention below?

This is the previous attempt to enable VMD ASPM:
https://lore.kernel.org/linux-pci/20200930082455.25613-1-kai.heng.feng@canonical.com/

It didn't enable LTR though.

Right now the downstream kernel use PCI quirk to enable VMD ASPM and LTR:
https://kernel.ubuntu.com/git/ubuntu/unstable.git/commit/?id=069ab00c2613d27cb7cdeb2a4c751de89dab81b4
https://kernel.ubuntu.com/git/ubuntu/unstable.git/commit/?id=1e4dec5fe846f8dd8954b173434670f8ae30b5ff

The patches don't touch VMD driver to minimize merge conflict on VMD driver.
I really hope we can put these changes to upstream VMD driver.

Kai-Heng

>
> > So what other options do we have if we want to enable VMD ASPM while
> > keeping CONFIG_PCIEASPM_DEFAULT=y?  Right now we enabled the VMD
> > ASPM/LTR bits in downstream kernel, but other distro users may want
> > to have upstream support for this.