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How to use device tree to get a rotary-encoder device

Question asked by Michael Nehls on Feb 25, 2020
Latest reply on Mar 3, 2020 by Michael Nehls

What I want to do:
Create a rotary encoder device in Linux with Yocto Project and device tree (/dev/rotary-encoder). The device should be visible after boot, so that it can be used in user space.


My Hardware:
i.MX8M Mini Evaluation Board (imx8mm evk)
Rotary encoder using two GPIOs


What I tried:
I changed the dts file and added code for the rotary encoder (tmp/work-shared/imx8mmevk/kernel-source/arch/arm64/boot/dts/freescale/fsl-imx8mm-evk.dts):

/ {

    rotary-encoder {
        compatible = "rotary-encoder";
        status = "okay";
        gpios = <&pca6416 14 GPIO_ACTIVE_HIGH>, <&pca6416 13 GPIO_ACTIVE_HIGH>;
        linux,axis = <0>; /* REL_X */
        rotary-encoder,encoding = "gray";


What is the right way and do I maybe need some device driver in addition to the device tree file? I thought Linux would have one for rotary encoders. The problem is that my knowledge about device trees is limited. I tried to find a solution via google, but couldn't. Maybe someone can help how to integrate this with the evaluation board.