pcie-brcmstb: failed to enter low-power link state (L23)

Hi,
I did some experiments with s2idle on Raspberry Pi 4 (8 GB RAM,
arm64/defconfig) and noticed that pcie-brcmstb fails to enter L23 state
during suspend. I don't have any clue about PCI or this specific IP.

Here is my current working branch [1], because s2idle on BCM2711
currently requires some quirks.

In order to help, I just added a simple dump of possible relevant
registers at the begin of brcm_pcie_enter_l23():

[   46.822440] PM: suspend entry (s2idle)
[   47.050887] Filesystems sync: 0.228 seconds
[   47.152159] Freezing user space processes
[   47.154443] Freezing user space processes completed (elapsed 0.002
seconds)
[   47.154472] OOM killer disabled.
[   47.154475] Freezing remaining freezable tasks
[   47.155742] Freezing remaining freezable tasks completed (elapsed
0.001 seconds)
[   48.797565] PM: suspend of devices complete after 1641.374 msecs
[   48.797580] PM: start suspend of devices complete after 1641.829 msecs
[   48.798059] PM: late suspend of devices complete after 0.473 msecs
[   48.810510] brcm-pcie fd500000.pcie:
PCIE_RC_CFG_PRIV1_LINK_CAPABILITY: 00315e12
[   48.810519] brcm-pcie fd500000.pcie: PCIE_RC_CFG_PRIV1_ROOT_CAP: 0000000f
[   48.810523] brcm-pcie fd500000.pcie: PCIE_MISC_HARD_PCIE_HARD_DEBUG:
00200000
[   48.810528] brcm-pcie fd500000.pcie: PCIE_MISC_MISC_CTRL: 88003480
[   48.810532] brcm-pcie fd500000.pcie: PCIE_MISC_PCIE_CTRL: 00000000
[   48.810535] brcm-pcie fd500000.pcie: PCIE_MISC_PCIE_STATUS: 000000b0
[   48.846632] brcm-pcie fd500000.pcie: failed to enter low-power link state
[   48.846640] xhci_hcd 0000:01:00.0: Possible wake-up device;
regulators will not be disabled
[   48.846725] PM: noirq suspend of devices complete after 48.628 msecs
[   48.846730] PM: suspend-to-idle
[   53.672017] PM: Triggering wakeup from IRQ 25
[   53.672032] PM: resume from suspend-to-idle

Does BCM2711 support L23 mode?

Best regards

[1] - https://github.com/lategoodbye/linux-dev/commits/v6.12-pm_v2/