[SteamOS 3.9.5 / cecd] S3 suspend/resume race conditions: immediate re-suspend on wake, user.slice freeze before TV standby TX, and HDMI 2.1 link training failure against cold TV

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Valutazione

Difficoltà
5/5
Tempo stimato
Più di una settimana
Idoneità per principianti
25/100
Tipo di issue
Bug
Chiarezza
Abbastanza chiara
Stato di attività
Attiva
Stack tecnologico
linux
Ambito
backend-api-design, operating-systems

Direzione di ricerca

Start by tracing cecd's PrepareForSleep handling and CEC transmit completion, then inspect the suspend and resume logs in the issue. The report also points to amdgpu_dm_handle_vrr_transition, connector hotplug handling, and DRM link retraining. Done means validating the proposed grace period, sleep delay inhibitor, and post-wake retraining across all three reported failures.

Scritto dal modello di indicizzazione a partire dal testo della issue.

Descrizione

System Information
  • SteamOS Version: 3.9.5 (20261023.100)
  • Kernel: 7.2.7-valve2-2-neptune-72-g31504582a073
  • Dock: Official Steam Deck Docking Station (4.0.0.0, DP-1)
  • Display: Samsung Q90A Neo QLED (0.0.0.0, HDMI 4, 2560x1440 @ 120Hz VRR HDR)
  • Audio: Samsung HW-S800B eARC Soundbar (3.0.0.0, HDMI 3)
Summary

Following up on #2968 (which fixed cecd deactivating when an eARC soundbar is present on the bus), we've hit three interrelated suspend/resume race conditions in cecd and amdgpu/Dock link training during S3 sleep/wake transitions:

1. False-Standby Bounce Loop on Resume (allow_standby = true)

When waking the Steam Deck from S3 sleep (e.g. via wireless controller while the TV is in standby), cecd thaws with user.slice and immediately processes either a buffered STANDBY (0x36) frame or a transitional standby state from the TV before the TV has finished waking up. Within ~1 second of PM: suspend exit, cecd requests systemd-logind to suspend the Steam Deck right back to sleep:

Oct 27 16:52:15 steamdeck kernel: PM: suspend exit
Oct 27 16:52:15 steamdeck cecd[1898]: INFO cecd::device: TV did not respond to wake immediately
Oct 27 16:52:15 steamdeck systemd-sleep[107509]: Successfully thawed unit 'user.slice'.
Oct 27 16:52:15 steamdeck systemd-logind[1138]: Operation 'suspend' finished.
Oct 27 16:52:16 steamdeck systemd-logind[1138]: suspend requested from client PID 1898 ('cecd') (unit [email protected])...
Oct 27 16:52:16 steamdeck systemd-logind[1138]: The system will suspend now!

Suggested Fix (Zero downside for working TVs):
Add a short post-resume grace window (e.g. 5–10 seconds after PrepareForSleep(false) / waking) during which incoming CEC STANDBY broadcasts from the TV are ignored by cecd.

2. user.slice Freeze Race Before STANDBY TX Completes (suspend_tv = true)

When putting the Steam Deck to sleep, cecd runs inside [email protected] (user.slice). Because CEC bus transmission + retries take ~200–600ms (especially if bus arbitration is busy), systemd-sleep frequently freezes user.slice or tears down the display topology before cecd's STANDBY transmission completes, leaving the TV turned on.

Suggested Fix (Zero downside for working TVs):
Hold the systemd-logind sleep delay inhibitor lock in cecd until the kernel CEC_TX_STATUS callback confirms the STANDBY message has finished transmitting (or timed out) before releasing the lock.

3. Cold-Boot HDMI 2.1 Link Training Failure ("Mode Not Supported" at 1440p@120Hz HDR)

When resuming from S3 sleep while connected to a TV in cold standby:

  1. At T+0.0s, kernel dm_resume immediately attempts DisplayPort/HDMI 2.1 link training (2560x1440 @ 120Hz HDR) via the Official Dock before the TV's high-bandwidth HDMI 2.1 receiver (Samsung Input Signal Plus) has booted: 
    Oct 27 16:52:15 steamdeck kernel: WARNING: drivers/gpu/drm/amd/amdgpu/../display/amdgpu_dm/amdgpu_dm.c:10439 at amdgpu_dm_handle_vrr_transition+0x1d5/0x1e0 [amdgpu]
Oct 27 16:52:18 steamdeck kernel: amdgpu 0000:04:00.0: [drm] *ERROR* dpcd_set_link_settings:1123: core_link_write_dpcd (DP_DOWNSPREAD_CTRL) failed
Oct 27 16:52:18 steamdeck kernel: amdgpu 0000:04:00.0: [drm] *ERROR* dpcd_set_link_settings:1128: core_link_write_dpcd (DP_LANE_COUNT_SET) failed
  2. cecd wakes the TV (IMAGE_VIEW_ON), and ~2.5s later the TV's HDMI 2.1 receiver finishes booting and switches to the Deck's input (ACTIVE_SOURCE).
  3. However, because the TV keeps +5V/HPD asserted during standby and the Dock's DP-to-HDMI bridge does not fire a new HPD interrupt once the TV's scaler finishes booting, amdgpu never re-trains the failed link—resulting in a permanent "Mode Not Supported" error on the TV until the cable is replugged or hotplug is forced.

Workaround / Suggested Fix:
If the TV was in standby (pwr-state != on) prior to wake, triggering a DRM connector hotplug/re-train (trigger_hotplug / KMS link re-verification) ~1.5s after the TV finishes waking and accepts ACTIVE_SOURCE cleanly re-trains the 2-lane HBR3 link and resolves the "Mode Not Supported" error 100% of the time without affecting TVs that were already powered on.

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