[Steam Machine][AMDGPU] 4K 120Hz unavailable on TCL C825 in Desktop and Game Mode; Game Mode also limited to 60 FPS at 1440p

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linux
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devtools, operating-systems

Hướng nghiên cứu

Start by reviewing the attached EDID, KScreen modes, DRM connector modes, and AMDGPU/kernel display logs; the issue names edid-decode and kscreen-doctor -o as ways to inspect display capabilities. Determine why CTA VIC 118 is absent from available modes, including whether EDID range limits or HDMI FRL/PCON negotiation affect validation. Then investigate Game Mode refresh selection and the reported 60 FPS limit separately, and document a reproducible cause and fix.

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Mô tả

Your system information
  • Steam client version: Not recorded (can be provided if needed)
  • SteamOS version: 3.9.5 — Build 20261023.100
  • Opted into Steam client beta?: Not confirmed
  • Opted into SteamOS beta?: No (Stable branch)
  • Have you checked for updates in Settings > System?: Yes

Hardware:

  • Device: Valve Steam Machine
  • GPU: AMD Navi 33 [1002:7481], using amdgpu
  • Kernel: 7.2.7-valve2-2-neptune-72-g31504582a073
  • Display: TCL C825, 4K 120Hz television
  • Connection: Direct HDMI connection (HDMI-A-1)
Please describe your issue in as much detail as possible:

The Steam Machine does not provide the expected 4K 120Hz output when connected to a TCL C825 television, despite the TV advertising 3840x2160 @ 120Hz and HDMI 2.1 FRL capability in its EDID.

The issue affects both Desktop Mode and Game Mode, with different symptoms.

Expected behavior:

  • Desktop Mode should offer 3840x2160 @ 120Hz.
  • Game Mode should support 4K 120Hz output on this display.
  • At 2560x1440 @ 120Hz, games should be able to exceed 60 FPS when supported by the game and its settings.

Actual behavior — Desktop Mode:

  • 3840x2160 @ 60Hz is available.
  • 2560x1440 @ 120Hz is available and works.
  • 1920x1080 @ 120Hz is available.
  • 3840x2160 @ 120Hz is missing entirely.

Disabling HDR and VRR does not make 4K 120Hz available.

Actual behavior — Game Mode:

  • 4K 120Hz output is not available.
  • Selecting 2560x1440 did not result in 120 FPS operation in the games tested.
  • The official Steam performance overlay continued to report a maximum of 60 FPS.
  • This behavior differs from Desktop Mode, where 2560x1440 @ 120Hz is available and operational.

The Steam FPS overlay does not independently confirm the physical HDMI output refresh rate, so further investigation may be needed to determine whether the Game Mode behavior is caused by the display refresh configuration, frame-rate limiting, VSync, or another factor.

EDID evidence:

VIC 118: 3840x2160 120.000000 Hz
Pixel clock: 1188.000000 MHz

HDMI Forum Vendor-Specific Data Block:
Maximum TMDS Character Rate: 600 MHz
SCDC Present
Max Fixed Rate Link:
  3 and 6 Gbps per lane on 3 lanes
  6, 8, 10 and 12 Gbps on 4 lanes

VRR range: 48–120 Hz

Kernel evidence:

amdgpu 0000:03:00.0: [drm] DP-HDMI FRL PCON supported

The driver reports FRL PCON capability, but the collected logs do not establish whether FRL negotiation succeeds or fails.

The EDID also contains legacy display range limits that differ from the HDMI 2.1 capabilities advertised in the CTA extension. This might be relevant to mode validation.

Troubleshooting performed:

  • Tested different HDMI cables and television HDMI inputs.
  • Confirmed 4K 60Hz operation.
  • Confirmed 1440p 120Hz operation in Desktop Mode.
  • Tested 1440p in Game Mode, where games remained at a maximum of 60 FPS according to the Steam performance overlay.
  • Disabled HDR and VRR without resolving the missing 4K 120Hz mode.
  • Verified the EDID using edid-decode.
  • Checked available modes using kscreen-doctor -o.
  • Collected AMDGPU and kernel display logs.
  • Confirmed the issue on SteamOS build 20261023.100 and kernel 7.2.7.
  • The television has previously supported 4K 120Hz output from an Xbox Series S.

Possible areas to investigate:

  • AMDGPU HDMI FRL / DP-to-HDMI PCON negotiation.
  • DRM mode validation for CTA VIC 118.
  • Handling of EDID range limits versus CTA HDMI 2.1 capabilities.
  • Game Mode display refresh-rate selection and frame-rate limiting.

The root cause has not yet been confirmed.

Steps for reproducing this issue:
  1. Connect a Valve Steam Machine directly to a TCL C825 4K 120Hz television via HDMI.
  2. Boot SteamOS and enter Desktop Mode.
  3. Open System Settings → Display Configuration and inspect the available modes. 3840x2160 @ 120Hz is missing.
  4. Select 2560x1440 @ 120Hz and confirm that this mode works in Desktop Mode.
  5. Return to Game Mode and attempt to use 4K 120Hz. The expected mode is unavailable.
  6. Select 2560x1440 in Game Mode and launch a game.
  7. Enable the official Steam performance overlay. In the games tested, the displayed frame rate remained limited to 60 FPS rather than reaching 120 FPS.
  8. Disable HDR and VRR and recheck the available display modes. The missing 4K 120Hz mode remains unresolved.
Diagnostic attachments

The collected diagnostic archive includes:

  • SteamOS and kernel information
  • GPU and driver information
  • KScreen display modes
  • DRM connector modes
  • Raw and decoded EDID
  • HDMI connector diagnostics
  • AMDGPU/kernel display logs

The available diagnostics primarily document Desktop Mode and the DRM/AMDGPU display capabilities. The Game Mode FPS behavior was observed separately using the official Steam performance overlay.

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