dcn_regdump

Utility for dumping HDMI-related registers from the AMD GPU Display Core Next (DCN). Supports DCN 3.2.x (RX 7000 series) and DCN 4.x.x (RX 9000 series), and any other generation with header files present in dcn_reg/.

Warning: Only run this on hardware with matching register definitions in dcn_reg/. Running on an unsupported GPU may cause a crash.

Dependencies

• iotools — must be in PATH
• lspci (from pciutils)
• Must be run as root

Usage

sudo ./dcn_regdump.sh

The script automatically detects the DCN version from dmesg and selects the appropriate register definitions. Output is printed to stdout; redirect to a file to save a log:

sudo ./dcn_regdump.sh | tee dcn_regdump.$(date +%Y%m%d-%H%M%S).log

Capturing logs with a GPU passthrough VM

The typical workflow for capturing registers in a specific GPU/display state (e.g. Windows with a particular driver or display config) is:

1. Boot a Windows VM with the AMD GPU passed through (e.g. via VFIO/QEMU). The GPU is now fully controlled by the Windows guest driver.

2. On the Linux host, while the VM is running, run the script:

   sudo ./dcn_regdump.sh | tee my_capture.log
   

   The host can still access the GPU's MMIO registers directly through the PCI BAR even while the GPU is owned by the guest.

3. To capture multiple states (e.g. before and after plugging in a display, or with audio playing vs. silent), run the script once per state and save each to a separate log file.

Register definitions

Register offset and shift/mask definitions live in dcn_reg/ as C headers extracted from the Linux kernel's amdgpu driver source. The script also accepts preprocessed flat .txt versions (dcn321_regs.txt, dcn410_regs.txt, etc.) which are faster to load if present.

To add support for a new DCN generation, drop the corresponding dcn_X_Y_Z_offset.h and dcn_X_Y_Z_sh_mask.h files into dcn_reg/.