My display doesn't offer upscaling resolutions. However, amdgpu.dc=1 + xf86-video-amdgpu does.
When I change the resolution from native (2560x1440) to one of those automatically offered upscaling resolutions (e.g. 1920x1080), the value in "/sys/class/drm/card0/device/pp_dpm_mclk" gets set to default.

I changed it before like this (to prevent flickering with 75Hz with my display):

echo "manual" > /sys/class/drm/card0/device/power_dpm_force_performance_level
echo "2" >  /sys/class/drm/card0/device/pp_dpm_mclk

The VRAM runs with its maximum clock as long as I don't change resolution. When I change the resolution like described above, the VRAM clock again gets dynamically changed according to load, which introduces nasty flickering in my case.

The desired behavior would be that the change done to pp_dpm_mclk remains untouched when changing to a GPU upscaling resolution.

I haven't checked if pp_dpm_sclk is affected as well. Other powerplay/overdrive/fan settings remain untouched by resolution change.

Using latest linux-amd-staging-drm-next-wip-git kernel.
Xorg session