Confirm on Lenovo ideapad 520S-14IKB (Intel i5-7gen, Nvidia 940MX , Intel 620HD).
On Ubuntu 17.10 (Nvidia driver 390.48 from ppa:graphics-drivers/ppa ppa:graphics-drivers/ppa) prime-select worked fine.
On Ubuntu 18.04 prime-select not turn off nvidia (driver from ppa and driver from repository).
Nouveau and bumblebee switches the graphics card well.
I noticed a different output of the command: cat /sys/kernel/debug/vgaswitcheroo/switch
nouveau driver:
0:IGD:+:Pwr:0000:00:02.0
1:DIS: :DynOff:0000:01:00.0
nvidia 390.48, after prime-select intel:
0:IGD:+:Pwr:0000:00:02.0
1:DIS: :Off:0000:01:00.0
You can see the different status of the discrete card. When "DunOff" it really disconnected from the power supply, and in case of "Off" it continues to consume energy. If it matters.
Confirm on Lenovo ideapad 520S-14IKB (Intel i5-7gen, Nvidia 940MX , Intel 620HD). drivers/ ppa ppa:graphics- drivers/ ppa) prime-select worked fine.
On Ubuntu 17.10 (Nvidia driver 390.48 from ppa:graphics-
On Ubuntu 18.04 prime-select not turn off nvidia (driver from ppa and driver from repository).
Nouveau and bumblebee switches the graphics card well.
I noticed a different output of the command: cat /sys/kernel/ debug/vgaswitch eroo/switch
nouveau driver: :Pwr:0000: 00:02.0 0000:01: 00.0
0:IGD:+
1:DIS: :DynOff:
nvidia 390.48, after prime-select intel: :Pwr:0000: 00:02.0
0:IGD:+
1:DIS: :Off:0000:01:00.0
You can see the different status of the discrete card. When "DunOff" it really disconnected from the power supply, and in case of "Off" it continues to consume energy. If it matters.