Tested successfully on Kubuntu 25.10

[mvmiller12]

Built custom kernel with this patch for Kubuntu 25.10 and confirmed this is working with Radeon 9070XT direct connected via HDMI to LG cx65 TV. Now running 4K 120Hz HDR VRR 16-Bit color, Full RGB Range. Confirmed.

[Danny3]

The TV supports more than 10-bit color?

[mvmiller12]

KDE reports that it automatically selected 16-bit color for the TV. The TV Manual states this TV supports 12-bit color output. This implies either KDE is lying OR the TV accepts the 16-bit color signal but is only displaying 12-bit color.

Specific TV Model is 2025 LG OLED65CXPUA

Note: If the computer is started and boots to Linux prior to the TV being turned on, there is only a black screen. Resetting the computer with the TV on resolves this.

[mkopec]

4K120 4:4:4 16bit would require DSC even at the highest FRL rate HDMI 2.1 allows, and DSC is currently unimplemented, so I don't think the GPU is actually sending 16bit.

What does cat /sys/kernel/debug/dri/1/*/amdgpu_current_bpc show? You need to run it as root

[mvmiller12]

Apologies for late response - life issues. I attempted to run the command you specified and it just errors out, even with SUDO. Looking in the directory, I saw a bunch of files and folders, so I assumed you were trying to find that string in one of them, so I attempted to GREP them and that is not working either. I even went to that folder AS root ans it did not work. I am pretty new to Linux overall but I did successfully compile and install the kernel with a bit of help from the post on the Reddit about compiling for CachyOS and some more help from our good buddy Google.

Here are the files in that directory. If you know which particular one I should be looking in, let me know and I'll crack it open to look.

drwxr-xr-x 2 root root           0 Feb 22 08:34 DP-1
drwxr-xr-x 2 root root           0 Feb 22 08:34 DP-2
drwxr-xr-x 2 root root           0 Feb 22 08:34 DP-3
drwxr-xr-x 3 root root           0 Feb 22 08:34 HDMI-A-1
drwxr-xr-x 2 root root           0 Feb 22 08:34 Writeback-1
--w------- 1 root root           0 Feb 22 08:34 amdgpu_benchmark
-rw------- 1 root root           0 Feb 22 08:34 amdgpu_compute_sched_mask
-r--r--r-- 1 root root           0 Feb 22 08:34 amdgpu_discovery
-r--r--r-- 1 root root           0 Feb 22 08:34 amdgpu_dm_capabilities
-rw-r--r-- 1 root root           0 Feb 22 08:34 amdgpu_dm_dcc_en
-rw-r--r-- 1 root root           0 Feb 22 08:34 amdgpu_dm_disable_hpd
-rw-r--r-- 1 root root           0 Feb 22 08:34 amdgpu_dm_dmcub_trace_event_en
-rw-r--r-- 1 root root           0 Feb 22 08:34 amdgpu_dm_dmub_fw_state
-rw-r--r-- 1 root root           0 Feb 22 08:34 amdgpu_dm_dmub_trace_mask
-rw-r--r-- 1 root root           0 Feb 22 08:34 amdgpu_dm_dmub_tracebuffer
-rw-r--r-- 1 root root           0 Feb 22 08:34 amdgpu_dm_dp_ignore_cable_id
-rw-r--r-- 1 root root           0 Feb 22 08:34 amdgpu_dm_dp_set_mst_en_for_sst
-rw-r--r-- 1 root root           0 Feb 22 08:34 amdgpu_dm_dtn_log
-rw-r--r-- 1 root root           0 Feb 22 08:34 amdgpu_dm_force_timing_sync
-rw-r--r-- 1 root root           0 Feb 22 08:34 amdgpu_dm_skip_detection_link_training
-rw-r--r-- 1 root root           0 Feb 22 08:34 amdgpu_dm_trigger_hpd_mst
-rw-r--r-- 1 root root           0 Feb 22 08:34 amdgpu_dm_visual_confirm
--w------- 1 root root           0 Feb 22 08:34 amdgpu_error_comp_1.0.0
--w------- 1 root root           0 Feb 22 08:34 amdgpu_error_comp_1.0.1
--w------- 1 root root           0 Feb 22 08:34 amdgpu_error_comp_1.1.0
--w------- 1 root root           0 Feb 22 08:34 amdgpu_error_comp_1.1.1
--w------- 1 root root           0 Feb 22 08:34 amdgpu_error_gfx_0.0.0
--w------- 1 root root           0 Feb 22 08:34 amdgpu_error_jpeg_dec
--w------- 1 root root           0 Feb 22 08:34 amdgpu_error_mes_3.0.0
--w------- 1 root root           0 Feb 22 08:34 amdgpu_error_mes_3.1.0
--w------- 1 root root           0 Feb 22 08:34 amdgpu_error_sdma0
--w------- 1 root root           0 Feb 22 08:34 amdgpu_error_sdma1
--w------- 1 root root           0 Feb 22 08:34 amdgpu_error_vcn_unified_0
-r-------- 1 root root           0 Feb 22 08:34 amdgpu_evict_gtt
-r-------- 1 root root           0 Feb 22 08:34 amdgpu_evict_vram
-r--r--r-- 1 root root           0 Feb 22 08:34 amdgpu_fence_info
-r--r--r-- 1 root root           0 Feb 22 08:34 amdgpu_firmware_info
--w------- 1 root root           0 Feb 22 08:34 amdgpu_force_sclk
-r-------- 1 root root           0 Feb 22 08:34 amdgpu_gca_config
-r--r--r-- 1 root root           0 Feb 22 08:34 amdgpu_gds_mm
-r--r--r-- 1 root root           0 Feb 22 08:34 amdgpu_gem_info
-r-------- 1 root root           0 Feb 22 08:34 amdgpu_gfxoff
-r-------- 1 root root           0 Feb 22 08:34 amdgpu_gfxoff_count
-r-------- 1 root root           0 Feb 22 08:34 amdgpu_gfxoff_residency
-r-------- 1 root root           0 Feb 22 08:34 amdgpu_gfxoff_status
-r-------- 1 root root           0 Feb 22 08:34 amdgpu_gpr
-r-------- 1 root root           0 Feb 22 08:34 amdgpu_gprwave
-r--r--r-- 1 root root           0 Feb 22 08:34 amdgpu_gpu_recover
-r--r--r-- 1 root root           0 Feb 22 08:34 amdgpu_gtt_mm
-r--r--r-- 1 root root           0 Feb 22 08:34 amdgpu_gws_mm
-r--r--r-- 1 root root           0 Feb 22 08:34 amdgpu_iomem
-r--r--r-- 1 root root        2048 Feb 22 08:34 amdgpu_mqd_comp_1.0.0
-r--r--r-- 1 root root        2048 Feb 22 08:34 amdgpu_mqd_comp_1.0.1
-r--r--r-- 1 root root        2048 Feb 22 08:34 amdgpu_mqd_comp_1.1.0
-r--r--r-- 1 root root        2048 Feb 22 08:34 amdgpu_mqd_comp_1.1.1
-r--r--r-- 1 root root        2048 Feb 22 08:34 amdgpu_mqd_gfx_0.0.0
-r--r--r-- 1 root root           0 Feb 22 08:34 amdgpu_mqd_mes_3.0.0
-r--r--r-- 1 root root           0 Feb 22 08:34 amdgpu_mqd_mes_3.1.0
-r--r--r-- 1 root root           0 Feb 22 08:34 amdgpu_mst_topology
-r--r--r-- 1 root root           0 Feb 22 08:34 amdgpu_oa_mm
-r--r--r-- 1 root root           0 Feb 22 08:34 amdgpu_pm_info
-rw------- 1 root root           0 Feb 22 08:34 amdgpu_preempt_ib
-r-------- 1 root root      524288 Feb 22 08:34 amdgpu_regs
-r-------- 1 root root           0 Feb 22 08:34 amdgpu_regs2
-r-------- 1 root root           0 Feb 22 08:34 amdgpu_regs_didt
-r-------- 1 root root           0 Feb 22 08:34 amdgpu_regs_pcie
-r-------- 1 root root           0 Feb 22 08:34 amdgpu_regs_smc
-r--r--r-- 1 root root        8204 Feb 22 08:34 amdgpu_ring_comp_1.0.0
-r--r--r-- 1 root root        8204 Feb 22 08:34 amdgpu_ring_comp_1.0.1
-r--r--r-- 1 root root        8204 Feb 22 08:34 amdgpu_ring_comp_1.1.0
-r--r--r-- 1 root root        8204 Feb 22 08:34 amdgpu_ring_comp_1.1.1
-r--r--r-- 1 root root        8204 Feb 22 08:34 amdgpu_ring_gfx_0.0.0
-r--r--r-- 1 root root        4108 Feb 22 08:34 amdgpu_ring_jpeg_dec
-r--r--r-- 1 root root       32780 Feb 22 08:34 amdgpu_ring_mes_3.0.0
-r--r--r-- 1 root root       32780 Feb 22 08:34 amdgpu_ring_mes_3.1.0
-r--r--r-- 1 root root        8204 Feb 22 08:34 amdgpu_ring_sdma0
-r--r--r-- 1 root root        8204 Feb 22 08:34 amdgpu_ring_sdma1
-r--r--r-- 1 root root        4108 Feb 22 08:34 amdgpu_ring_vcn_unified_0
-r--r--r-- 1 root root           0 Feb 22 08:34 amdgpu_sa_info
-rw------- 1 root root           0 Feb 22 08:34 amdgpu_sdma_sched_mask
-r-------- 1 root root           0 Feb 22 08:34 amdgpu_sensors
-rw------- 1 root root           0 Feb 22 08:34 amdgpu_smu_debug
-r-------- 1 root root           0 Feb 22 08:34 amdgpu_test_ib
-r--r--r-- 1 root root           0 Feb 22 08:34 amdgpu_vbios
-r--r--r-- 1 root root           0 Feb 22 08:34 amdgpu_vm_info
-r--r--r-- 1 root root 17095983104 Feb 22 08:34 amdgpu_vram
-r--r--r-- 1 root root           0 Feb 22 08:34 amdgpu_vram_mm
-r-------- 1 root root           0 Feb 22 08:34 amdgpu_wave
-r--r--r-- 1 root root           0 Feb 22 08:34 clients
drwxr-xr-x 3 root root           0 Feb 22 08:34 crtc-0
drwxr-xr-x 3 root root           0 Feb 22 08:34 crtc-1
drwxr-xr-x 3 root root           0 Feb 22 08:34 crtc-2
drwxr-xr-x 3 root root           0 Feb 22 08:34 crtc-3
drwxr-xr-x 2 root root           0 Feb 22 08:34 encoder-0
drwxr-xr-x 2 root root           0 Feb 22 08:34 encoder-1
drwxr-xr-x 2 root root           0 Feb 22 08:34 encoder-2
drwxr-xr-x 2 root root           0 Feb 22 08:34 encoder-3
drwxr-xr-x 2 root root           0 Feb 22 08:34 encoder-4
drwxr-xr-x 2 root root           0 Feb 22 08:34 encoder-5
drwxr-xr-x 2 root root           0 Feb 22 08:34 encoder-6
drwxr-xr-x 2 root root           0 Feb 22 08:34 encoder-7
drwxr-xr-x 2 root root           0 Feb 22 08:34 encoder-8
-r--r--r-- 1 root root           0 Feb 22 08:34 framebuffer
-r--r--r-- 1 root root           0 Feb 22 08:34 gem_names
-r--r--r-- 1 root root           0 Feb 22 08:34 internal_clients
-r--r--r-- 1 root root           0 Feb 22 08:34 name
-r--r--r-- 1 root root    33554432 Feb 22 08:34 psp_spirom_dump
-r--r--r-- 1 root root           0 Feb 22 08:34 state
drwxr-xr-x 2 root root           0 Feb 22 08:34 ta_if
-r--r--r-- 1 root root           0 Feb 22 08:34 ttm_page_pool