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.
