archive mirror
 help / color / mirror / Atom feed
From: Bjorn Helgaas <>
To: Kai-Heng Feng <>
Cc: Bjorn Helgaas <>,,
	Lorenzo Pieralisi <>,
	Rob Herring <>,,,
	Ian Kumlien <>
Subject: Re: [PATCH 2/2] PCI: vmd: Enable ASPM for mobile platforms
Date: Mon, 5 Oct 2020 14:19:30 -0500	[thread overview]
Message-ID: <20201005191930.GA3031652@bjorn-Precision-5520> (raw)
In-Reply-To: <>

[+cc Ian, who's also working on an ASPM issue]

On Tue, Oct 06, 2020 at 02:40:32AM +0800, Kai-Heng Feng wrote:
> > On Oct 3, 2020, at 06:18, Bjorn Helgaas <> wrote:
> > On Wed, Sep 30, 2020 at 04:24:54PM +0800, Kai-Heng Feng wrote:
> >> BIOS may not be able to program ASPM for links behind VMD, prevent Intel
> >> SoC from entering deeper power saving state.
> > 
> > It's not a question of BIOS not being *able* to configure ASPM.  I
> > think BIOS could do it, at least in principle, if it had a driver for
> > VMD.  Actually, it probably *does* include some sort of VMD code
> > because it sounds like BIOS can assign some Root Ports to appear
> > either as regular Root Ports or behind the VMD.
> > 
> > Since this issue is directly related to the unusual VMD topology, I
> > think it would be worth a quick recap here.  Maybe something like:
> > 
> >  VMD is a Root Complex Integrated Endpoint that acts as a host bridge
> >  to a secondary PCIe domain.  BIOS can reassign one or more Root
> >  Ports to appear within a VMD domain instead of the primary domain.
> > 
> >  However, BIOS may not enable ASPM for the hierarchies behind a VMD,
> >  ...
> > 
> > (This is based on the commit log from 185a383ada2e ("x86/PCI: Add
> > driver for Intel Volume Management Device (VMD)")).
> Ok, will just copy the portion as-is if there's patch v2 :)
> > But we still have the problem that CONFIG_PCIEASPM_DEFAULT=y means
> > "use the BIOS defaults", and this patch would make it so we use the
> > BIOS defaults *except* for things behind VMD.
> > 
> >  - Why should VMD be a special case?
> Because BIOS doesn't handle ASPM for it so it's up to software to do
> the job.  In the meantime we want other devices still use the BIOS
> defaults to not introduce any regression.
> >  - How would we document such a special case?
> I wonder whether other devices that add PCIe domain have the same
> behavior?  Maybe it's not a special case at all...

What other devices are these?

> I understand the end goal is to keep consistency for the entire ASPM
> logic. However I can't think of any possible solution right now.
> >  - If we built with CONFIG_PCIEASPM_POWERSAVE=y, would that solve the
> >    SoC power state problem?
> Yes.
> >  - What issues would CONFIG_PCIEASPM_POWERSAVE=y introduce?
> This will break many systems, at least for the 1st Gen Ryzen
> desktops and laptops.
> All PCIe ASPM are not enabled by BIOS, and those systems immediately
> freeze once ASPM is enabled.

That indicates a defect in the Linux ASPM code.  We should fix that.
It should be safe to use CONFIG_PCIEASPM_POWERSAVE=y on every system.

Are there bug reports for these?  The info we would need to start with
includes "lspci -vv" and dmesg log (with CONFIG_PCIEASPM_DEFAULT=y).
If a console log with CONFIG_PCIEASPM_POWERSAVE=y is available, that
might be interesting, too.  We'll likely need to add some
instrumentation and do some experimentation, but in principle, this
should be fixable.


  reply	other threads:[~2020-10-05 19:19 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-30  8:24 [PATCH 1/2] PCI/ASPM: Add helper to enable ASPM link Kai-Heng Feng
2020-09-30  8:24 ` [PATCH 2/2] PCI: vmd: Enable ASPM for mobile platforms Kai-Heng Feng
2020-10-02 22:18   ` Bjorn Helgaas
2020-10-05 18:40     ` Kai-Heng Feng
2020-10-05 19:19       ` Bjorn Helgaas [this message]
2020-10-07  4:26         ` Kai-Heng Feng
2020-10-07  9:28           ` Ian Kumlien
2020-10-07 13:30           ` Bjorn Helgaas
2020-10-07 13:44             ` Ian Kumlien
2020-10-08  4:19             ` Kai-Heng Feng
2020-10-09 14:34               ` Ian Kumlien

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20201005191930.GA3031652@bjorn-Precision-5520 \ \ \ \ \ \ \ \ \ \

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).