If no logging on a Huawi phone then dial 

*#*#2846579#*#*
On the Y7 it doesn't need Dial pressed

or on a Huawei tablet (e.g. MediaPad M3), launch the Huawei Calculator in landscape and enter
()()2846579()() 
The T3 7 needs '=' pressed, the M3 Lite 8 doesn't

You will see a hidden menu. 

Go to the Project Menu > Background Setting > Log setting and define the log availability (log switch) and level (log level setting).
The actual menu may differ depending on the device.

If it doesn't work straight away then restart your phone.