Audio Amp SHIM (3W Mono Amp) by Pimoroni dts for Radxa Zero3W

pimoroni-dac.dts

/dts-v1/;
/plugin/;

#include <dt-bindings/gpio/gpio.h>
#include <dt-bindings/pinctrl/rockchip.h>

/ {
	// This metadata is for tools like dietpi-config
	metadata {
		title = "Enable Pimoroni Audio Amp SHIM on I2S3-M0";
		compatible = "radxa,zero3"; // Specifically for Radxa Zero 3
		category = "audio";
		exclusive = "GPIO3_A4", "GPIO3_A5", "GPIO3_A6", "i2s3_2ch"; // Pins 12, 35, 40
		description = "Enables the Pimoroni Audio Amp SHIM on the I2S3 interface.";
	};
};

// This fragment adds nodes to the root of the device tree
&{/} {
	// 1. Define the Codec.
	// We are now using the compatible string for the actual chip on the board,
	// as we have manually compiled and installed its driver.
	max98357a_codec: max98357a-codec {
		compatible = "maxim,max98357a";
		#sound-dai-cells = <0>;
		status = "okay";
	};

	// 2. Define the Sound Card, linking the CPU's I2S to the Codec
	pimoroni_shim_sound: pimoroni-shim-sound {
		compatible = "simple-audio-card";
		simple-audio-card,name = "Pimoroni-Amp-SHIM"; // This name will appear in ALSA
		simple-audio-card,format = "i2s";

		// Add address and size cells to define the format for the 'reg' property
		#address-cells = <1>;
		#size-cells = <0>;

		// This defines the link between the board and the DAC
		simple-audio-card,dai-link@0 {
			reg = <0>;
			format = "i2s";
			// FINAL FIX: Explicitly define the link as mono (1 channel)
			// to match the MAX98357A hardware and driver.
			channels = <1>;

			// CPU side of the link
			cpu {
				sound-dai = <&i2s3_2ch>; // Using the Zero 3's I2S3 interface
			};

			// Codec side of the link
			codec {
				sound-dai = <&max98357a_codec>; // Linking to our MAX98357A codec above
			};
		};
	};
};

// 3. Enable the I2S3 controller and assign the correct pins used by the SHIM
&i2s3_2ch {
	pinctrl-0 = <&i2s3m0_sclk  // Pin 12 (BCK)
			&i2s3m0_lrck  // Pin 35 (LRCK)
			&i2s3m0_sdo>;  // Pin 40 (DIN)
	status = "okay";
};

// 4. Disable any conflicting interfaces.
// The I2S3 pins are multiplexed with I2C3. We must disable I2C3
// to prevent resource conflicts.
&i2c3 {
	status = "disabled";
};

// 5. Disable the built-in HDMI audio to prevent resource conflicts.
// The node is called "hdmi-sound" and its label is "hdmi_sound".
&hdmi_sound {
	status = "disabled";
};

sudo apt install -y device-tree-compiler build-essential

mkdir -p /boot/overlay-user/dt-bindings/pinctrl
mkdir -p /boot/overlay-user/dt-bindings/gpio

wget -O /boot/overlay-user/dt-bindings/pinctrl/rockchip.h https://raw.githubusercontent.com/radxa/kernel/linux-6.1-stan-rkr5.1/include/dt-bindings/pinctrl/rockchip.h
wget -O /boot/overlay-user/dt-bindings/gpio/gpio.h https://raw.githubusercontent.com/radxa/kernel/linux-6.1-stan-rkr5.1/include/dt-bindings/gpio/gpio.h

cpp -nostdinc -undef -x assembler-with-cpp -E -I . /boot/overlay-user/pimoroni-dac.dts | dtc -@ -I dts -O dtb -o /boot/overlay-user/pimoroni-dac.dtbo -

in /boot/dietpiEnv.txt:
user_overlays=pimoroni-dac

then:
sudo reboot

before loading the device tree overlay, prepare the codec driver

wget https://mirrors.dotsrc.org/armbian-apt/pool/main/l/linux-headers-vendor-rk35xx/linux-headers-vendor-rk35xx_25.5.1_arm64__6.1.115-S5271-Dca91-P09c0-C26e6H2313-HK01ba-Vc222-Ba566-R448a.deb
sudo dpkg -i linux-headers-vendor-rk35xx_25.5.1_arm64__6.1.115-S5271-Dca91-P09c0-C26e6H2313-HK01ba-Vc222-Ba566-R448a.deb
sudo apt-get -f install

ls /lib/modules/$(uname -r)/build

mkdir -p ~/driver_build
cd ~/driver_build

wget https://raw.githubusercontent.com/torvalds/linux/v6.1/sound/soc/codecs/max98357a.c
nano Makefile

add this:

obj-m += snd-soc-max98357a.o
snd-soc-max98357a-objs := max98357a.o

all:
	make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules

clean:
	make -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean

then:

make
sudo cp snd-soc-max98357a.ko /lib/modules/$(uname -r)/kernel/sound/soc/codecs/

sudo depmod -a
sudo modprobe snd-soc-max98357a

verify:

lsmod | grep max98357a

zcat /proc/config.gz | grep MAX98357