GPIO pin configuration using Devicetree

[piotrosiotr]

Hello. 

I have several custom boards based on NRF52832 QFAA chip. Pin mappings on these boards are slightly different, but the purposes are the same, so I want to use one project with different pinouts. AFAIK, the right way to do it is creating dts/overlay file for each board and using different build configurations for each one. Am I  on a right way?

So, the question itself is: for example, I need to control power supply using GPIO pin. On each board pin number of this pin varies (e.g. GPIO10 on one board and GPIO11 on another). The function of this pin is to toggle MOSFET switch (Output, Push-Pull). I want to give a name to this exact pin in dts/overlay file and to reference it from code by name, so if I want to select another board,  I don't need to change my code, just select another board. So in theory it should work like this: 

1. Add child node that represents the pin to gpio0 label in overlay file:

&gpio0 {
    status = "okay";
    gpio_power_pin : power_pin {
        gpios = <&gpio0 10 (GPIO_ACTIVE_HIGH | GPIO_PUSH_PULL)>;
    };
};

2. Reference it from code by node id: 

const struct device *power_pin_dev = DEVICE_DT_GET(DT_NODELABEL(gpio_power_pin));

3. Use it in a common way.

But this does not works. On building, I get the following error:

C:\ncs\v2.2.0\zephyr\include\zephyr\device.h:83:41: error: '__device_dts_ord_DT_N_NODELABEL_gpio_power_pin_ORD' undeclared here (not in a function)
83 | #define DEVICE_NAME_GET(dev_id) _CONCAT(__device_, dev_id)

In which way do I need to modify my project to get it work?

[Vidar Berg]

Hi,

You were on the right track by using the device tree to assign the control pin. However, in order to define a new node as you did, you also need to select a suitable device tree binding by using the 'compatible' property.

Since you will be using the output to control power, it would make sense to select the 'regulator-fixed'' binding and add CONFIG_REGULATOR=y to your prj.conf file. This will enable the Regulator subsystem in your application.

Here is an example I made for this:

regulator_example.zip

Best regards,

Vidar

[piotrosiotr]

OK, thank you, that works perfectly for me. But I've got another question: what if I want to create a custom devicetree binding for a "compatible" property? How to deal with it? For example, I have a shift register on my board and I want to declare in dts file and use it like a usual gpio pin. Should I create a custom driver for it? In which way I should use "compatible" property?

[Vidar Berg]

My coworker Marte has posted a sample to demonstrate how you can add custom bindings on GitHub. You can find it here: https://github.com/martelmy/NCS_examples/tree/main/devicetree/devicetree_custom_device. Additionally, there is a similar sample available in Zephyr: https://developer.nordicsemi.com/nRF_Connect_SDK/doc/latest/zephyr/samples/basic/custom_dts_binding/README.html.

Optionally, you can create an out-of-tree driver as shown in this sample: https://developer.nordicsemi.com/nRF_Connect_SDK/doc/latest/zephyr/samples/application_development/out_of_tree_driver/README.html.