[PPC] Boot problems after the pci-v6.18-changes

[Bjorn Helgaas]

On Wed, Oct 15, 2025 at 10:13:04AM +0200, Herve Codina wrote:
> ...

> I also observed issues with the commit f3ac2ff14834 ("PCI/ASPM: Enable all
> ClockPM and ASPM states for devicetree platforms")
> 
> My system is an ARM board (Marvel Armada 3720 DDB)
>   https://elixir.bootlin.com/linux/v6.17.1/source/arch/arm64/boot/dts/marvell/armada-3720-db.dts
> 
> I use an LAN966x PCI board
>   https://elixir.bootlin.com/linux/v6.17.1/source/drivers/misc/lan966x_pci.c
> 
> Usually, when I did a ping using the PCI board, I have more or less the
> following timings:
>    # ping 192.168.32.100
>    PING 192.168.32.100 (192.168.32.100): 56 data bytes
>    64 bytes from 192.168.32.100: seq=0 ttl=64 time=3.328 ms
>    64 bytes from 192.168.32.100: seq=1 ttl=64 time=2.636 ms
>    64 bytes from 192.168.32.100: seq=2 ttl=64 time=2.928 ms
>    64 bytes from 192.168.32.100: seq=3 ttl=64 time=2.649 ms
> 
> But with a vanilla v6.18-rc1 kernel, those timings become awful:
>    # ping 192.168.32.100
>    PING 192.168.32.100 (192.168.32.100): 56 data bytes
>    64 bytes from 192.168.32.100: seq=0 ttl=64 time=656.634 ms
>    64 bytes from 192.168.32.100: seq=1 ttl=64 time=551.812 ms
>    64 bytes from 192.168.32.100: seq=2 ttl=64 time=702.966 ms
>    64 bytes from 192.168.32.100: seq=3 ttl=64 time=725.904 ms
> 
> Reverting commit f3ac2ff14834 ("PCI/ASPM: Enable all ClockPM and
> ASPM states for devicetree platforms") fixes my timing issues.

We expect *some* performance impact from enabling ASPM, but this seems
excessive.  You should be able to control the ASPM settings for an
individual device via sysfs:

  https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/ABI/testing/sysfs-bus-pci?id=v6.17-rc1#n431

My guess is that L1.2 is enabled and the threshold values in the L1 PM
Substates control registers are bogus.  I don't know how to fix those,
especially on a devicetree system.  But it might be possible to fiddle
with them using setpci (while ASPM is disabled).  Not for the faint of
heart.

Bjorn