Using Analog Devices Inc. AD7091R ADC on Raspberry Pi (driver availible: AD7476), using ADI-Kuiper-Linux, how to create a linux device tree file

Question

ADC ad7091r connected to Raspberry Pi but does not work yet

I am trying to create a dts file for the AD7091r analog-to-digital converter, it is supposed to talk over SPI with the Linux on the Raspberry Pi.

The device is supported with the driver "AD7476".

On the electronic side, I have a developer board from Analog Devices Inc. for the ad7091r connected. It is plugged in connected through PMOD, using an Digilent Designspark PMod Hat Adapter.

Now I think the next step is to add a line in the /boot/config.txt, like dtoverlay=abcdef. For the AD7091r there is no compiled .dtbo device tree file, so I would need to create one.

Here I do not know what to put. How can I get the device running?

The ADC is supposed to show up in:

ls /sys/bus/iio/devices/iio\:device0 `

checking driver in kernel config

Using the arm linux image from Analog Device, ADI Kuiper Linux, flashed it on sdcard and booted it up. Then I had a look at the kernel config of it:

# enable access to the kernel configuration which is in use and save it
sudo modprobe configs
zcat /proc/config.gz > actual.config

Cloned the ADI Kuiper linux kernel and checked what modules are enabled by loading that config into menuconfig:

git clone https://github.com/analogdevicesinc/linux
cd linux
git checkout rpi-6.1.y
make menuconfig // <load> actual.config

I can find there that following is marked build-in with * -> Device Drivers -> Industrial I/O support -> Analog to digital converters -> Analog Devices AD7476 1-channel ADCs driver and other similar devices from AD and TI.

trying to create a device tree overlay

I tried to compile the example from https://wiki.analog.com/resources/tools-software/linux-drivers/iio-adc/ad7091r8 with just editing the device name, naming the file ad7091r.dts:

    // SPDX-License-Identifier: GPL-2.0

    /dts-v1/;
    /plugin/;

    include <dt-bindings/interrupt-controller/irq.h>
    include <dt-bindings/gpio/gpio.h>

    / {
        compatible = "brcm,bcm2835", "brcm,bcm2711";
    };

    &gpio {
        ad7091r_pins: ad7091r_pins {
            brcm,pins = <22>; // interrupt
            brcm,function = <0>; // input
        };
    };

    &spi0 {
        status = "okay";

        cs-gpios = <&gpio 8 GPIO_ACTIVE_LOW>;

        ad7091r@0 {
            compatible = "adi,ad7091r";
            reg = <0x0>;
            spi-max-frequency = <1000000>;
            convst-gpios = <&gpio 25 GPIO_ACTIVE_LOW>;
            reset-gpios = <&gpio 27 GPIO_ACTIVE_LOW>;
            pinctrl-names = "default";
            pinctrl-0 = <&ad7091r_pins>;
            interrupt-parent = <&gpio>;
            interrupts = <22 IRQ_TYPE_EDGE_FALLING>;
        };
    };

    &spidev0 {
        status = "disabled";
    };

    &spidev1 {
        status = "disabled";
    };

But it does not even compile using:

dtc -O dtb -o ad7091r.dto ad7091r.dts

The output is:

Error: ad7091r.dts:6.1-8 syntax error
FATAL ERROR: Unable to parse input tree