[drm:si_dpm_set_power_state [amdgpu]] *ERROR* si_resume_smc failed

On a Dell OptiPlex 5055 Ryzen CPU/0P03DX, BIOS 1.1.20 05/31/2019, Linux 6.6.12 does not show AMDGPU warnings.

Rebooting to Linux 6.8-rc6, it warns:

[drm:si_dpm_set_power_state [amdgpu]] *ERROR* si_resume_smc failed

Powering off the system, and booting Linux 6.8-rc6, the two warnings below are logged:

[drm:si_dpm_set_power_state [amdgpu]] *ERROR* si_enable_smc_cac failed
[drm:si_dpm_set_power_state [amdgpu]] *ERROR* si_set_sw_state failed

1. Linux 6.6.12 messages
2. Linux 6.8-rc6 (two unrelated USB patches) after rebooting
3. Linux 6.8-rc6 (two unrelated USB patches) after powering off and then booting