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no CEC with CAC-2504

Updated on 07-10-2026 in Adapters and Cables
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2 on 09-09-2026

I have a CAC-2504 connected to an Intel USB-C DP Alt Mode port. Video works at 3840×2160@60. Linux supports DP CEC tunneling and recognizes the CAC-2504 as an HDMI DP branch device, but the adapter reports DPCD register 0x3000 = 0x00. Linux therefore does not create /dev/cec0. The Linux kernel documentation lists CAC-2504 as a known-working CEC-tunneling adapter. Is there a firmware update for this adapter that enables/fixes DP CEC tunneling? I have seen references to firmware 11.116.007 for CAC-2504.

  • CAC-2504 connected via USB-C DP Alt Mode.
  • 3840×2160@60 works.
  • Kernel 7.2.0.
  • CONFIG_DRM_DISPLAY_DP_AUX_CEC=y.
  • drm_dp_cec_attach() is definitely called.
  • The adapter’s DPCD revision is 1.4.
  • DPCD 0x3000 = 0x00, meaning it does not advertise DP CEC tunneling.
  • Consequently Linux doesn’t create /dev/cec0.
  • Linux documentation nevertheless lists CAC-2504 as a known-working DP-CEC adapter.
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Marjoristro 0 on 01-10-2026

hi

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pleaseds 0 on 07-10-2026

This sounds like a frustrating bug, especially when the documentation says it should work. It makes me wonder how many other niche hardware issues like this exist. Finding a firmware update seems like the most logical next step; hopefully, Club 3D can provide one. It’s a bit like trying to find the perfect build in Pokerogue , you know?

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