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

[Kai-Heng Feng]

On Wed, Oct 27, 2021 at 12:53 AM Bjorn Helgaas <helgaas@xxxxxxxxxx> 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@xxxxxxxxxxxxx/

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.