AC adapter detection not functioning on Acer Predator Helios 500 Ryzen Edition when DPM enabled on AMDGPU free.
The Acer Predator Helios 500 Ryzen Edition laptop fails to detect the AC adapter input when DPM is enabled for AMDGPU. The issue causes the Ryzen 2700 CPU and Vega 56 GPU to operate in low power mode. Removing and inserting the AC adapter reflects change to the battery charge % in ACPI and resolves the CPU acting in low power state, but the GPU remains in low power and ACPI does not detect the change to the AC adapter.
Originally this issue was reported as an ACPI issue on the following kernel bugzilla thread which goes into further detail. The AC adapter works as intended on kernels that predate Vega support (I tested 4.14), or when either nomodeset or amdgpu.dpm=0 arguments are placed in initramfs on 4.19 and above. Only amdgpu.dpm=0 allows for a full boot with operating display manager, the CPU having proper power management, and AC adapter detection; though the GPU remains in the lowest power state. Nomodeset prevents use of the DM entirely. I have attached tgz of the system when booted with amdgpu.dpm=0 set at boot as well as when it is in a default configuration. I am currently running Manjaro Linux on kernel 5.4, though I have reproduced the error on Kernels 5.3 and 4.19.
Some items of note: Under normal conditions the AC adapter light behavior shows AC detected when the kernel begins to load. The light extinguishes when the display adapter initiates during bootup and ACPI events stop being detected for the AC adapter. Also, in the bugzilla thread this comment indicated when the linux-firmware started to have an affect on kernel 4.18. However, I used the downgrade utility in Manjaro to revert to linux-firmware 20190424.4b on kernel 5.4 but it had no effect. I also built the ACPI kernel module from git before the 4.19 commits and it also had no effect.
I have also reproduced the error in Ubuntu 19.04.