Notes on Driver amdgpu
Based on Linux GPU driver documentation for amdgpu
Kernel option amdgpu.dc (Display Core)
Disable/Enable Display Core driver for debugging (1 = enable, 0 = disable). The default is -1 (automatic for each asic).
| amdgpu.dc value | Meaning |
|---|---|
| 0 | disable Display Core |
| 1 | enable Display Core |
| default = -1 | enable/disable based on asic |
TODO: insert list of GPUs supporting DC
Kernal option amdgpu.hw_i2c
To enable hw i2c engine. Only affects non-DC display handling. The default is 0 (Disabled).
amdgpu.hw_i2c (applies only if Display Core disabled)
| amdgpu.hw_i2c value | Meaning |
|---|---|
| 0 (default) | disable |
| 1 | enable |
| Tested on RX580 (Ellesmere), Kernel 5.13 |
Name in /sys/bus/i2c/devices/i2c-N/name
Case 1: Display Core disabled and hw_i2c=0
| Connector | Name |
|---|---|
| DVI, HDMI | AMDGPU i2c bit bus 0xNN |
| DP: | CardM-DP-N, e.g. Card0-DP-1 |
Case 2: Display Core disabled and hw_i2c=1
Connector | Name
----------|----------
DVI, HDMI | AMDGPU i2c hw bus 0xNN
DP: | CardM-DP-N, e.g. Card0-DP-1
I2C communication fails on DVI and HDMI
Case 3: Display Core enabled
Connector | Name
----------|----------
DVI, HDMI | AMDGPU DM i2c hw bus 0x9N
DP: | AMDGPU DM aux hw bus N
Where is /sys/bus/i2c/devices/i2c-name set?
Message Format | Message Source -------------------------|---------------- AMDGPU DM aux hw bus N | drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c AMDGPU i2c hw bus 0xNN | drivers/gpu/drm/amd/amdgpu/amdgpu_i2c.c AMDGPU i2c bit bus 0xNN | drivers/gpu/drm/amd/amdgpu/amdgpu_i2c.c
If Display Dore is enabled, a line containining either "Display Core initialized" or "Display Core failed to initialize" is found in the system log. Message source: drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c, drivers/gpu/drm/amd/display/dc/core/dc.c To check:
# egrep -e "Kernel command line|Display Core" /var/log/syslog