Subject: linux-image-6.18.15+deb13-amd64: suspend via s2idle fails to reach S0i3 on ThinkPad T14s Gen 4 AMD, while 6.12.74 works

Package: linux-image-6.18.15+deb13-amd64
Version: 6.18.15-1~bpo13+1
Severity: important
Tags: upstream

Dear Debian Kernel Team,

I am reporting what appears to be a suspend regression in the Debian backports
kernel on a Lenovo ThinkPad T14s Gen 4 AMD (type 21F8CTO1WW).

Summary
-------
On linux-image-6.18.15+deb13-amd64 (6.18.15-1~bpo13+1), suspend enters s2idle
but fails to reach S0i3 / deep low-power idle. The laptop "suspends", but the
fan keeps running and power draw remains high.

On the same machine, the Debian security kernel
linux-image-6.12.74+deb13+1-amd64 (6.12.74-2) works correctly: s2idle reaches
S0i3 successfully and the machine suspends properly.

System
------
- Model: Lenovo ThinkPad T14s Gen 4 AMD (21F8CTO1WW)
- CPU: AMD Ryzen 7 PRO 7840U
- BIOS before testing: 1.25
- BIOS updated during debugging via fwupd to: 1.29
- mem_sleep: [s2idle]
- The platform exposes S0/S4/S5 only; no "deep"/S3 is available

Regression comparison
---------------------
Working kernel:
- linux-image-6.12.74+deb13+1-amd64
- version 6.12.74-2

Failing kernel:
- linux-image-6.18.15+deb13-amd64
- version 6.18.15-1~bpo13+1

Both kernels were tested on the same machine and firmware.

Behavior on failing kernel (6.18.15-1~bpo13+1)
-----------------------------------------------
Relevant journal excerpts from the failing boot:

  Linux version 6.18.15+deb13-amd64 #1 SMP PREEMPT_DYNAMIC Debian 6.18.15-1~bpo13+1
  ACPI: PM: (supports S0 S4 S5)
  Low-power S0 idle used by default for system suspend
  systemd-sleep: Performing sleep operation 'suspend'...
  PM: suspend entry (s2idle)
  amd_pmc AMDI0009:00: Last suspend didn't reach deepest state
  systemd-sleep: System returned from sleep operation 'suspend'
  PM: suspend exit

During testing on 6.18, AMD PMC debugfs showed:
- S0ix Residency Time: 0
- Last S0i3 Status: Unknown/Fail

Observed user-visible effect:
- laptop appears suspended
- but fan keeps spinning
- opening the lid resumes the machine

Behavior on working kernel (6.12.74-2)
--------------------------------------
On 6.12.74+deb13+1-amd64, the same machine suspends correctly.

AMD PMC debugfs on the working 6.12 kernel reports:
- Last S0i3 Status: Success
- Time in S0i3: 9852905 us
- Residency Time: 9852905

This strongly suggests a regression between the two Debian kernel versions.

What was already tested
-----------------------
- BIOS updated from 1.25 to 1.29: no fix for 6.18 behavior
- acpi.ec_no_wakeup=1: no fix for 6.18 behavior
- Suspend tested with and without USB-C dock attached
- Suspend tested with dock-side USB/Thunderbolt wake settings adjusted
- The separate lid-close/logind issue was fixed independently and is unrelated

Potentially relevant hardware path
----------------------------------
This platform includes AMD Pink Sardine USB4/Thunderbolt controllers:
- 0000:c5:00.5
- 0000:c5:00.6

While debugging 6.18, amd_pmc debug output suggested USB4 activity remained
significant when suspend failed, but the regression remains reproducible even
after disconnecting the dock.

Installed package versions
--------------------------
- linux-image-6.18.15+deb13-amd64: 6.18.15-1~bpo13+1
- linux-image-6.12.74+deb13+1-amd64: 6.12.74-2
- amd64-microcode: 3.20250311.1
- firmware-linux / firmware-linux-nonfree: 20260110-1~bpo13+1

If needed, I can provide additional logs, but the key point is:
- 6.18 backports fails to reach S0i3 on suspend
- 6.12 on the same machine succeeds

Thanks.

Control: reassign -1 src:linux 6.18.15-1
Control: tags -1 + moreinfo

As we won't provide more updates to kernels with the 6.18 series, and
moved to 6.19 (with a bpo upload pending as well yet), can you confirm
if the issue persists with 6.19.8-1 from unstable?

Regards,
Salvatore

I would like to mention that I think this is the same bug I have hit.

I am using Debian Stable but BACKPORTS kernels on a new-ish (Dec 2025) :

Thinkpad P14s Gen6 AMD

I pass the kernel boot parameter :

amdgpu.dcdebugmask=0x10

to fix some X/screen issues (slow redraw, lock-ups).

Suspend works when I close the laptop lid.

However, updating to the last backport kernel "6.18.15+deb13" caused
suspend to break. The laptop seems to suspend on lid close (red lid
light starts flashing normally) but in the morning the laptop is warm
and the battery has drained.

To summarise :

6.18.12+deb13-amd64 -- ok

6.18.15+deb13-amd64 -- BAD suspend

I installed the latest "testing" kernel "6.19.6+deb14+1" and suspend
works OK again.

6.19.6+deb14+1-amd64 - ok

In case it is useful, I attach the output of lspci.


Cheers,