When using the hardware monitoring interface to change pwm1_enable to 2 (automatic) from 1 (manual), the automatic fan control does not work as expected. Instead, the pwm1 value keeps jumping around between at least two values and a continuous, persisting, and unpleasantly high-pitched sound can be heard from inside the computer case. The only way to stop those things is writing some valid value to pwm1, which in turn also switches pwm1_enable back to 1. If the system is booted without ever manually changing the pwm1_enable value, which then defaults to 2, automatic fan control does work as intended.

I am using a custom RX 580 (Sapphire Nitro+ Radeon RX 580 8GD5 Special Edition) on a Gentoo x86_64 system and was able to reproduce the issue with the 4.17.0 kernel with Gentoo patches, the Ubuntu kernel on the 18.04 image (should be a 4.15 one) and also with amd-staging-drm-next.