Screen blanks for a second whenever discrete GPU is powered up
On this Kaby Lake G laptop, GNOME Shell blanks the screen for a second each time the AMD GPU is powered up. Triggers for powering up include: launching something which loads GL such as Steam or glxinfo, loading the Display configuration page, and so on.
This behaviour does not occur with GNOME Shell under X, so it's probably something to do with mutter's KMS interactions.
Because the GPU powers down quite aggressively (I think it's about 5sec without activity) this can be quite annoying :)
It seems that powering up the discrete GPU causes mutter to re-probe the KMS outputs, which might be the culprit.
dmesg log with drm.debug=0x4 of a power-up/blank/power-down cycle