So the backlight is set to 255 most of the time (because with that value it is stable)... 
I have pressed the decrease and increase backlight buttons some times:

arg4 is different...
arg5 is 0x0 here too...


Aspire-A315-41:~$ sudo kprobe-perf 'p:dce_abm_set_backlight_level_pwm $arg1 $arg2 $arg3 $arg4 $arg5 '
Tracing kprobe dce_abm_set_backlight_level_pwm. Ctrl-C to end.
 mate-power-back-7094  [002] ....  4130.246969: dce_abm_set_backlight_level_pwm: (dce_abm_set_backlight_level_pwm+0x0/0x410 [amdgpu]) arg1=0xffff9cabd4c87800 arg2=0xf4fd arg3=0x0 arg4=0x1 arg5=0x0
 mate-power-back-7100  [002] ....  4140.650308: dce_abm_set_backlight_level_pwm: (dce_abm_set_backlight_level_pwm+0x0/0x410 [amdgpu]) arg1=0xffff9cabd4c87800 arg2=0xe9fb arg3=0x0 arg4=0x1 arg5=0x0
 mate-power-back-7106  [004] ....  4148.360022: dce_abm_set_backlight_level_pwm: (dce_abm_set_backlight_level_pwm+0x0/0x410 [amdgpu]) arg1=0xffff9cabd4c87800 arg2=0xf4fd arg3=0x0 arg4=0x1 arg5=0x0
 mate-power-back-7112  [006] ....  4150.064228: dce_abm_set_backlight_level_pwm: (dce_abm_set_backlight_level_pwm+0x0/0x410 [amdgpu]) arg1=0xffff9cabd4c87800 arg2=0xffff arg3=0x0 arg4=0x1 arg5=0x0
 mate-power-back-7117  [000] ....  4154.430645: dce_abm_set_backlight_level_pwm: (dce_abm_set_backlight_level_pwm+0x0/0x410 [amdgpu]) arg1=0xffff9cabd4c87800 arg2=0xf4fd arg3=0x0 arg4=0x1 arg5=0x0
 mate-power-back-7123  [000] ....  4156.020204: dce_abm_set_backlight_level_pwm: (dce_abm_set_backlight_level_pwm+0x0/0x410 [amdgpu]) arg1=0xffff9cabd4c87800 arg2=0xe9fb arg3=0x0 arg4=0x1 arg5=0x0
 mate-power-back-7129  [000] ....  4169.318284: dce_abm_set_backlight_level_pwm: (dce_abm_set_backlight_level_pwm+0x0/0x410 [amdgpu]) arg1=0xffff9cabd4c87800 arg2=0xf4fd arg3=0x0 arg4=0x1 arg5=0x0
 mate-power-back-7135  [003] ....  4171.173554: dce_abm_set_backlight_level_pwm: (dce_abm_set_backlight_level_pwm+0x0/0x410 [amdgpu]) arg1=0xffff9cabd4c87800 arg2=0xffff arg3=0x0 arg4=0x1 arg5=0x0
 mate-power-back-7141  [006] ....  4177.134779: dce_abm_set_backlight_level_pwm: (dce_abm_set_backlight_level_pwm+0x0/0x410 [amdgpu]) arg1=0xffff9cabd4c87800 arg2=0xf4fd arg3=0x0 arg4=0x1 arg5=0x0
 mate-power-back-7147  [000] ....  4178.988650: dce_abm_set_backlight_level_pwm: (dce_abm_set_backlight_level_pwm+0x0/0x410 [amdgpu]) arg1=0xffff9cabd4c87800 arg2=0xe9fb arg3=0x0 arg4=0x1 arg5=0x0
 mate-power-back-7152  [005] ....  4179.822378: dce_abm_set_backlight_level_pwm: (dce_abm_set_backlight_level_pwm+0x0/0x410 [amdgpu]) arg1=0xffff9cabd4c87800 arg2=0xdef9 arg3=0x0 arg4=0x1 arg5=0x0
 mate-power-back-7157  [003] ....  4180.801012: dce_abm_set_backlight_level_pwm: (dce_abm_set_backlight_level_pwm+0x0/0x410 [amdgpu]) arg1=0xffff9cabd4c87800 arg2=0xd3f7 arg3=0x0 arg4=0x1 arg5=0x0
 mate-power-back-7162  [003] ....  4181.676478: dce_abm_set_backlight_level_pwm: (dce_abm_set_backlight_level_pwm+0x0/0x410 [amdgpu]) arg1=0xffff9cabd4c87800 arg2=0xc8f5 arg3=0x0 arg4=0x1 arg5=0x0
 mate-power-back-7173  [004] ....  4186.458165: dce_abm_set_backlight_level_pwm: (dce_abm_set_backlight_level_pwm+0x0/0x410 [amdgpu]) arg1=0xffff9cabd4c87800 arg2=0xd3f7 arg3=0x0 arg4=0x1 arg5=0x0
 mate-power-back-7179  [000] ....  4186.989282: dce_abm_set_backlight_level_pwm: (dce_abm_set_backlight_level_pwm+0x0/0x410 [amdgpu]) arg1=0xffff9cabd4c87800 arg2=0xdef9 arg3=0x0 arg4=0x1 arg5=0x0
 mate-power-back-7184  [000] ....  4187.362960: dce_abm_set_backlight_level_pwm: (dce_abm_set_backlight_level_pwm+0x0/0x410 [amdgpu]) arg1=0xffff9cabd4c87800 arg2=0xe9fb arg3=0x0 arg4=0x1 arg5=0x0
 mate-power-back-7189  [002] ....  4187.737620: dce_abm_set_backlight_level_pwm: (dce_abm_set_backlight_level_pwm+0x0/0x410 [amdgpu]) arg1=0xffff9cabd4c87800 arg2=0xf4fd arg3=0x0 arg4=0x1 arg5=0x0
 mate-power-back-7194  [007] ....  4188.118618: dce_abm_set_backlight_level_pwm: (dce_abm_set_backlight_level_pwm+0x0/0x410 [amdgpu]) arg1=0xffff9cabd4c87800 arg2=0xffff arg3=0x0 arg4=0x1 arg5=0x0
^C
Ending tracing...