How to control GPIO using DT in Application?

BKwak.1 · ‎2021-01-28

I want to control defined GPIO in DT in Applicatoin code.

But I can't control this, please let me know how to control gpio with DT in applicatoin.

1) I can control GPIO in Application without DT . (unused at gpioinfo)

2) I can't control GPIO in application with DT, like below.

gpioinfo

line 14: unnamed "stm32mp:green:user" output active-low [used]

occurred error massage when running application code

Failed to issue GET LINEHANDLE IOCTL (-25)

Failed to issue GPIOHANDLE_SET_LINE_VALUES_IOCTL (-25)

reference code

https://wiki.st.com/stm32mpu/wiki/How_to_control_a_GPIO_in_userspace

Device Tree - add green led

led {

compatible = "gpio-leds";

blue {

label = "heartbeat";

gpios = <&gpiod 9 GPIO_ACTIVE_HIGH>;

linux,default-trigger = "heartbeat";

default-state = "off";

};

green {

label = "stm32mp:green:user";

gpios = <&gpioa 14 GPIO_ACTIVE_LOW>;

default-state = "on";

};

OlivierK · ‎2021-02-01

Hello BKwak.1 (Community Member),

You should care not to mix user space and kernel space. Either you control the GPIO in user space using gpiolib, like it is specified in:https://wiki.st.com/stm32mpu/wiki/How_to_control_a_GPIO_in_userspace

or you modify the DT and you control the GPIO in kernel space.

https://wiki.st.com/stm32mpu/wiki/How_to_control_a_GPIO_in_kernel_space

For the specific gpio-leds driver, you can refer to

https://wiki.st.com/stm32mpu/wiki/How_to_cross-compile_with_the_Developer_Package

Regards,

Olivier

BillR · ‎2021-03-18

Hi, so to be clear - Is there in fact no way to enable a pull-down at the low level, like (preferably) u-boot or kernel device tree, but then be able to control the GPIO from user space as we are now? We forgot an external pull down to a FET and would prefer not to rework it if possible.