CONFIG_BACKLIGHT_PWM is not set in the current/latest kernel. Turning it on doesn't help ``` zcat /proc/config.gz |grep BACKLIGHT CONFIG_SAMSUNG_DEV_BACKLIGHT=y # CONFIG_FB_BACKLIGHT is not set CONFIG_BACKLIGHT_LCD_SUPPORT=y CONFIG_BACKLIGHT_CLASS_DEVICE=y # CONFIG_BACKLIGHT_GENERIC is not set CONFIG_BACKLIGHT_PWM=m <--- turned on # CONFIG_BACKLIGHT_ADP8860 is not set # CONFIG_BACKLIGHT_ADP8870 is not set # CONFIG_BACKLIGHT_LM3630 is not set # CONFIG_BACKLIGHT_LM3639 is not set # CONFIG_BACKLIGHT_LP855X is not set CONFIG_HID_PICOLCD_BACKLIGHT=y CONFIG_LEDS_TRIGGER_BACKLIGHT=y ``` Boot messages: ``` $ dmesg | grep back [ 3.977660] pwm-backlight pwm-backlight.0: unable to request PWM, trying legacy API [ 3.982264] pwm-backlight pwm-backlight.0: unable to request legacy PWM [ 4.110729] platform pwm-backlight.0: Driver pwm-backlight requests probe deferral [ 4.289334] pwm-backlight pwm-backlight.0: unable to request PWM, trying legacy API [ 4.302308] pwm-backlight pwm-backlight.0: unable to request legacy PWM [ 4.311763] platform pwm-backlight.0: Driver pwm-backlight requests probe deferral [ 4.386515] pwm-backlight pwm-backlight.0: unable to request PWM, trying legacy API [ 4.394205] pwm-backlight pwm-backlight.0: unable to request legacy PWM [ 4.400775] platform pwm-backlight.0: Driver pwm-backlight requests probe deferral ``` Older XU kernel (latest, 3.4.91) has /sys/class/ entry for pwm-backlight.0 with working control files. This kernel has the directory, but no controls.