Re: My AlderLake Dell (XPS-9320) needs these patches to get full standby/low-power modes

David E. Box
2023-12-21T01:19:36Z

On Fri, 2023-11-17 at 16:21 -0800, David E. Box wrote:
> On Thu, 2023-11-16 at 17:18 -0600, Bjorn Helgaas wrote:
> > [+cc Matthew, author of 41cd766b0659 ("PCI: Don't enable aspm before drivers
> > have had a chance to veto it")]
> >
> > On Thu, Nov 16, 2023 at 12:10:02PM -0800, David E. Box wrote:
> > > On Tue, 2023-11-07 at 13:15 +0200, Mika Westerberg wrote:
> > > > On Mon, Nov 06, 2023 at 12:11:07PM -0600, Bjorn Helgaas wrote:
> > > > > On Sat, Nov 04, 2023 at 10:13:24AM -0700, Kenneth R. Crudup wrote:
> > > > > >
> > > > > > I have a Dell XPS-9320 with an Alderlake chipset, and the NVMe
> > > > > > behind a VMD device:
> > > > > >
> > > > > > ----
> > > > > > [    0.127342] smpboot: CPU0: 12th Gen Intel(R) Core(TM) i7-1280P
> > > > > > (family:
> > > > > > 0x6, model: 0x9a, stepping: 0x3)
> > > > > > ----
> > > > > > 0000:00:0e.0 0104: 8086:467f
> > > > > >         Subsystem: 1028:0af3
> > > > > >         Flags: bus master, fast devsel, latency 0, IOMMU group 9
> > > > > >         Memory at 603c000000 (64-bit, non-prefetchable) [size=32M]
> > > > > >         Memory at 72000000 (32-bit, non-prefetchable) [size=32M]
> > > > > > a7152be79b6        Memory at 6040100000 (64-bit, non-prefetchable)
> > > > > > [size=1M]
> > > > > >         Capabilities: <access denied>
> > > > > >         Kernel driver in use: vmd
> > > > > > ----
> > > > > >
> > > > > > The only release kernel that was able to get this laptop to
> > > > > > fully get into low-power (unfortunately only s0ix) was the
> > > > > > Ubuntu-6.2.0- ... series from Ubuntu (remote
> > > > > > git://git.launchpad.net/~ubuntu-
> > > > > > kernel/ubuntu/+source/linux/+git/lunar).
> > > > > >
> > > > > > I'd bisected it to the following commits (in this order):
> > > > > >
> > > > > > 4ff116d0d5fd PCI/ASPM: Save L1 PM Substates Capability for
> > > > > > suspend/resume
> > > > > > 5e85eba6f50d PCI/ASPM: Refactor L1 PM Substates Control Register
> > > > > > programming
> > > > > > 1a0102a08f20 UBUNTU: SAUCE: PCI/ASPM: Enable ASPM for links under
> > > > > > VMD
> > > > > > domain
> > > > > > 47c7bfd31514 UBUNTU: SAUCE: PCI/ASPM: Enable LTR for endpoints
> > > > > > behind
> > > > > > VMD
> > > > > > 154d48da2c57 UBUNTU: SAUCE: vmd: fixup bridge ASPM by driver name
> > > > > > instead
> > > > >
> > > > > Thanks for these.  You don't happen to have URLs for those Ubuntu
> > > > > commits, do you?  E.g., https://git.kernel.org/linus/4ff116d0d5fd
> > > > > (which was reverted by a7152be79b62 ("Revert "PCI/ASPM: Save L1 PM
> > > > > Substates Capability for suspend/resume"")).
> > > > >
> > > > > > Without the patches I never see Pkg%PC8 or higher(? lower?),
> > > > > > nor i915 states DC5/6, all necssary for SYS%LPI/CPU%LPI. I've
> > > > > > attached a little script I use alongside turbostat for
> > > > > > verifying low-power operation (and also for seeing what
> > > > > > chipset subsystem may be preventing it).
> > > > > >
> > > > > > The first two are in Linus' trees, but were reverted
> > > > > > (4ff116d0d5fd in a7152be79b6, 5e85eba6f50d in ff209ecc376a).
> > > > > > The last three come from Ubuntu's Linux trees (see remote spec
> > > > > > above). The first two remain reverted in the Ubuntu trees, but
> > > > > > if I put them back, I get increased power savings during
> > > > > > suspend/resume cycles.
> > > > > >
> > > > > > Considering the power draw is really significant without these
> > > > > > patches (10s of %s per hour) and I'd think Dell would have
> > > > > > sold some decent number of these laptops, I'd been patiently
> > > > > > waiting for these patches, or some variant to show up in the
> > > > > > stable trees, but so far I'm up to the 6.6 stable kernel and
> > > > > > still having to manually cherry-pick these, so I thought maybe
> > > > > > I could bring this to the PM maintainers' attention so at
> > > > > > least start a discussion about this issue.
> > > > >
> > > > > Thank you very much for raising this again.  We really need to make
> > > > > some progress, and Mika recently posted a patch to add the
> > > > > 4ff116d0d5fd functionality again:
> > > > > https://lore.kernel.org/r/20231002070044.2299644-1-mika.westerberg@linux.intel.com
> > > > >
> > > > > The big problem is that it works on *most* systems, but it still
> > > > > seems to break a few.  So Mika's current patch relies on a
> > > > > denylist of systems where we *don't* restore the substates.
> > > >
> > > > According to latest reports it is just that one system where this
> > > > is still an issue. The latest patch works in Asus UX305FA even if
> > > > it is not in the denylist. That would leave that one system only
> > > > to the denylist, at least the ones we are aware about.
> > >
> > > I've been working with Thomas, whose system is the last known to
> > > have problems with Mika's patch. It turns out that his config sets
> > > aspm_policy to 'powersave'.  If he sets it to any other policy,
> > > Mika's patch works [1]. It's possible that others may see the same
> > > issue if they use 'powersave' as well.
> > >
> > > The theory right now is that enabling L1SS in pci_restore_state() is
> > > too early.
> >
> > I'd really like to figure out what "too early" means.  We can make it
> > later by enabling L1SS somewhere else, but unless we know exactly what
> > needs to happen first, we're likely to break it again.  And if we know
> > what's required, we can probably figure out a cleaner way to restore
> > it.
>
> Still trying to understand this particular failure. The current patch to
> Thomas
> more closely mimics how ASPM is enabled during boot when powersave is set. If
> it
> works we can at least prove that we can get it to work again by using a
> similar
> flow.

With some free time I was able to find a system in our lab that reproduces the
same failure reported on the last problem report from Thomas. That is, with
powersave selected, the nvme fails to come up after resume from S3 with this
patch without a quirk. It's actually obvious when you can see the flow. We
observed that on S3 resume, BIOS has enabled L1.2 (likely back to preboot
setting). Restoring powersave will therefore disable L1.2. Per spec, L1.2 must
be disabled on the downstream first. But pci_restore_state() gets called on
upstream devices first. Indeed, on my system, clearing the L1.2 state on the
root port makes the nvme device inaccessible by the time
pci_aspm_restore_state() is called for it. I've modified the patch to defer L1SS
restore until the downstream component so they can be done together. The patch
clears L1.2 on the child first before the parent, restores both configs and then
reenables them in reverse on the parent then the child. This works on my system.
I've posted the patch as a V5 and on the bugzilla and appreciate if anyone here
can test.

https://lore.kernel.org/linux-pci/20231221011250.191599-1-david.e.box@linux.intel.com/

David