Use rotary encoder on stm32mp157

[Jason007]

I'm doing a project, that I need a rotary encoder working on cortex-a7 core of stm32mp157.

I met problem, my rotary encoder can not work. 

This is what I have done:

1. In kernel menuconfig I have config: use rotary encoder as a build-in module;

2. Write dts, and I am sure these gpio not been use anywhere:

    rotary@3 {

        compatible = "rotary-encoder";

        gpios = <&gpioa 0 GPIO_ACTIVE_LOW>, <&gpiog 3 GPIO_ACTIVE_LOW>;

        linux,axis = <6>;

        rotary-encoder,encoding = "gray";

        rotary-encoder,relative-axis;

        status = "okay";

    };

In dmesg I can see my roary is started

In /proc/device-tree, I can see the device node

In evtest nothing output, when I turn the knob of encoder.

what is the problem, I need your help, thank you!

[PatrickF]

HI @Jason007 

Did you have GPIOs pull-ups on the board ?

Maybe try if internal pull-up is ok by using

(GPIO_ACTIVE_LOW | GPIO_PULL_UP)

Alternatively (could reach higher count rate), you could use TIM or LPTIM for this (still need pull-ups).
See https://wiki.stmicroelectronics.cn/stm32mpu/wiki/How_to_use_the_IIO_user_space_interface#How_to_use_the_quadrature_encoder_with_the_sysfs_interface

(need to chose input pins according to Timers inputs possible muxing).

Regards,