Sysfs /sys/class/pwm not created

I built my own openwrt with sysfs file system and was able to cycle onboard LEDs with /sys/class/gpio but it seems that /sys/class/pwm for dimming it is missing.
How can I create it?

a search shows the device specific pwm0 and pwm1. It's a linkit 7688.

find -name "*pwm*"

I got sysfs showing pwm0 by installing kmod-pwm-mediatek-ramips but unfortunately it does not work, what is maybe no surprise because the package description says it's for a different Target from Mediatek: for 7628 not as I am searching for 7688.

Can somebody point me to the source location of kmod-pwm-mediatek-ramips?

Easily found in OpenWrt git...

Package definition;a=blob;f=target/linux/ramips/;h=b604110b1e3953166ce13816dbafdfc23fc099be;hb=HEAD#l10

Actual sources;a=blob;f=target/linux/ramips/patches-4.14/0052-pwm-add-mediatek-support.patch;h=6eb7f16b9db48c6575028b00d00173efb58f4d26;hb=HEAD