ADC_DT_SPEC_GET doesn't work for DT nodes other than /zephyr,user

RE: ADC_DT_SPEC_GET doesn't work for DT nodes other than /zephyr,user

Kenneth Goveas — Thu, 21 Sep 2023 11:19:43 GMT

Hi Naeem,

Ah, so every node mandatorily needs a compatible. This I did not know. Now that solves the problem. I just defined another DT binding as follows,

description: |
    Analog input channel.

compatible: analog-input

include: base.yaml

properties:
    io-channels:
        type: phandle-array
        required: true

and wrote my device tree node compatible with this binding,

/ {
    batt {
        compatible = "analog-input";
        io-channels = <&adc 0>;
    };
};

and now everything works just as I expect it to.

Thanks a lot for your help!

RE: ADC_DT_SPEC_GET doesn't work for DT nodes other than /zephyr,user

Naeem Maroof — Fri, 15 Sep 2023 10:33:25 GMT

Hi Kenneth,

I get what you are saying, and I can see that the ADC_DT_SPEC_GET_BY_IDX does not require "voltage-divider" compatibility.

However, when I try to define a node in the overlay, it immediately informs me that "compatible" is required property for a node.

(more info here: DTS Bindings and Devicetree Bindings)

And accordingly, the compatible will also enforce other properties, for example "output-ohms" is required property for "voltage-divider" compatible node.

RE: ADC_DT_SPEC_GET doesn't work for DT nodes other than /zephyr,user

Kenneth Goveas — Thu, 14 Sep 2023 17:06:12 GMT

Hi Naeem,

Thanks for your response. However, the Readme you mentioned is specific to the battery measurement sample. If you look into its C source code, it specifically looks for either /vbatt or /zephyr,user which is why the devicetree nodes must be named as such. In my source code, I use /batt to initialize the struct adc_dt_spec like this:

static struct adc_dt_spec _batt_spec = ADC_DT_SPEC_GET(DT_PATH(batt));

For this to work, the devicetree node should indeed be /batt and not /vbatt or /zephyr,user. Now, the weird thing is that this works if I define /batt with the "voltage-divider" compatible but not without it. According to Zephyr's documentation on ADC_DT_SPEC_GET and ADC_DT_SPEC_GET_BY_IDX, it should not be necessary to use the "voltage-divider" compatible. Simply defining the node with the io-channels property should suffice.

RE: ADC_DT_SPEC_GET doesn't work for DT nodes other than /zephyr,user

Naeem Maroof — Fri, 08 Sep 2023 12:37:08 GMT

Hello Kenneth,

As per Battery Measurement Readme, either the board devicetree should have a /vbatt node with "voltage-divider" compatible or the ADC config needs to be provided via zephyr,user node.

Compatible is required property for voltage divider node.

BR, Naeem