XHCI-PCI: existing allowlist for enabling auto-suspend/runtime-pm in the kernel vs a userspace allowlist ?

[Hans de Goede <hdegoede@redhat.com>]

Hi All,

ATM the kernel has a allowlist (coded as a big if) for XHCI-PCI controllers on
which to enable auto-suspend. This seems to consist solely of XHCI controllers
embedded inside Intel Thunderbolt controllers:

         if (pdev->vendor == PCI_VENDOR_ID_INTEL &&
             (pdev->device == PCI_DEVICE_ID_INTEL_ALPINE_RIDGE_2C_XHCI ||
              pdev->device == PCI_DEVICE_ID_INTEL_ALPINE_RIDGE_4C_XHCI ||
              pdev->device == PCI_DEVICE_ID_INTEL_ALPINE_RIDGE_C_2C_XHCI ||
              pdev->device == PCI_DEVICE_ID_INTEL_ALPINE_RIDGE_C_4C_XHCI ||
              pdev->device == PCI_DEVICE_ID_INTEL_TITAN_RIDGE_2C_XHCI ||
              pdev->device == PCI_DEVICE_ID_INTEL_TITAN_RIDGE_4C_XHCI ||
              pdev->device == PCI_DEVICE_ID_INTEL_TITAN_RIDGE_DD_XHCI ||
              pdev->device == PCI_DEVICE_ID_INTEL_ICE_LAKE_XHCI ||
              pdev->device == PCI_DEVICE_ID_INTEL_TIGER_LAKE_XHCI))
                 xhci->quirks |= XHCI_DEFAULT_PM_RUNTIME_ALLOW;

I noticed this because it seems that the product-id for the TB controller
in the Lenovo T14 gen 1 is missing: 8086:15c1

At the same time we also have a more generic allowlist for enabling
auto-suspend/runtime-pm in userspace:

https://github.com/systemd/systemd/blob/master/hwdb.d/60-autosuspend.hwdb

ATM this only contains USB device ids, but there also is a second hwdb
file, auto-generated baed on info from ChromeOS (to avoid having to
duplicate this info):

https://github.com/systemd/systemd/blob/master/tools/make-autosuspend-rules.py
https://github.com/systemd/systemd/blob/master/tools/chromiumos/gen_autosuspend_rules.py

As you can see this second file already contains a whole bunch of
(mostly Intel vendor) PCI vid:pid pairs and udev will enable
runtime-pm on these based on the auto generated hwdb file.

To me it seems better for future XHCI controllers on which we
want to auto-enable runtime-pm, such as the missing 8086:15c1
model in userspace, together with the allowlist for runtime-pm
on other PCI devices in userspace, rather then to add yet another
quirk for this to to xhci-pci.c code.

The downside would be that this is somewhat inconsistent with
how we have done this before, still I believe that it would
be better / easier to maintain this in userspace (hwdb) in the
future.

So I was wondering what other people think about this?

Regards,

Hans