GLAN blocks C-states deeper than C3

[crawfxrd]

• Model: TGL+
• BIOS version: system76/firmware-open@b22e8dee415b
• EC version:
• OS: Pop!_OS 22.04
• Kernel: 6.5.4-76060504-generic

The system will not go to C-states lower than C3 when idle.

Steps to reproduce

• Lock the screen, allowing the display to turn off
• Wait 1 minute
• Unlock the system
• sudo cat /sys/kernel/debug/pmc_core/package_cstate_show

Expected behavior

• C6 and C8 (and potentially C10) should report non-zero

Actual behavior

• All values below C3 are 0

Additional info

Power management for GLAN is disabled.

$ cat "/sys/bus/pci/devices/0000:2e:00.0/power/control"
on

Setting automatic power management will allow deeper C-states.

sudo sh -c "echo auto > '/sys/bus/pci/devices/0000:2e:00.0/power/control'"

[crawfxrd]

I'm not convinced GLAN config for boards is configured correctly (should we be using drivers/net?), so I'll leave this open until the configs can be checked.

I don't know what is disabling power management in the kernel. May be the kernel itself with all the commits mentioning ASPM problems I see in drivers/net/ethernet/realtek.