The RADXA ROCK 4D, like many other Rockchip-based boards, uses an ES8388
analog audio codec. On the production version of the board, the codec's
LOUT1 and ROUT1 pins are tied to the headphone jack, whereas pins LOUT2
and ROUT2 lead to a non-populated speaker amplifier that itself leads to
a non-populated speaker jack. The schematic is still haunted by the
ghosts of those symbols, but it clearly marks them as "NC".

The 3.5mm TRRS jack has its microphone ring (and ground ring) wired to
the codec's LINPUT1 and RINPUT1 pins for differential signalling.

Furthermore, it uses the SoCs ADC to detect whether the inserted cable
is of headphones (i.e., no microphone), or a headset (i.e., with
microphone). The way this is done is that the ADC input taps the output
of a 100K/100K resistor divider that divides the microphone ring pin
that's pulled up to 3.3V.

There is no ADC level difference between a completely empty jack and one
with a set of headphones (i.e., ones that don't have a microphone)
connected. Consequently headphone insertion detection isn't something
that can be done.

Add the necessary codec and audio card nodes. The non-populated parts,
i.e. LOUT2 and ROUT2, are not modeled at all, as they are not present on
the hardware.

Also, add an adc-keys node for the headset detection, which uses an
input type of EV_SW with the SW_MICROPHONE_INSERT keycode. Below the
220mV pressed voltage level of our SW_MICROPHONE_INSERT switch, we also
define a button that emits a KEY_RESERVED code, which is there to model
this part of the voltage range as not just being extra legroom for the
button above it, but actually a state that is encountered in the real
world, and should be recognised as a valid state for the ADC range to be
in so that no "closer" ADC button is chosen.

Signed-off-by: Nicolas Frattaroli <nicolas.frattaroli@collabora.com>
---
 arch/arm64/boot/dts/rockchip/rk3576-rock-4d.dts | 90 +++++++++++++++++++++++++
 1 file changed, 90 insertions(+)

diff --git a/arch/arm64/boot/dts/rockchip/rk3576-rock-4d.dts b/arch/arm64/boot/dts/rockchip/rk3576-rock-4d.dts
index 6756403111e704cad42f6674d5ab55eb0306f1e3..4d4b8ababd2436b82515443b029916b3c786dba1 100644
--- a/arch/arm64/boot/dts/rockchip/rk3576-rock-4d.dts
+++ b/arch/arm64/boot/dts/rockchip/rk3576-rock-4d.dts
@@ -6,6 +6,7 @@
 /dts-v1/;
 
 #include <dt-bindings/gpio/gpio.h>
+#include <dt-bindings/input/input.h>
 #include <dt-bindings/leds/common.h>
 #include <dt-bindings/pinctrl/rockchip.h>
 #include <dt-bindings/pwm/pwm.h>
@@ -37,6 +38,31 @@ hdmi_con_in: endpoint {
 		};
 	};
 
+	es8388_sound: es8388-sound {
+		compatible = "simple-audio-card";
+		simple-audio-card,format = "i2s";
+		simple-audio-card,mclk-fs = <256>;
+		simple-audio-card,name = "On-board Analog ES8388";
+		simple-audio-card,widgets = "Microphone", "Headphone Mic",
+					    "Headphone", "Headphone";
+		simple-audio-card,routing = "Headphone", "LOUT1",
+					    "Headphone", "ROUT1",
+					    "Left PGA Mux", "Differential Mux",
+					    "Differential Mux", "LINPUT1",
+					    "Differential Mux", "RINPUT1",
+					    "LINPUT1", "Headphone Mic",
+					    "RINPUT1", "Headphone Mic";
+
+		simple-audio-card,cpu {
+			sound-dai = <&sai1>;
+		};
+
+		simple-audio-card,codec {
+			sound-dai = <&es8388>;
+			system-clock-frequency = <12288000>;
+		};
+	};
+
 	leds: leds {
 		compatible = "gpio-leds";
 		pinctrl-names = "default";
@@ -57,6 +83,37 @@ user-led {
 		};
 	};
 
+	saradc_keys: adc-keys {
+		compatible = "adc-keys";
+		io-channels = <&saradc 3>;
+		io-channel-names = "buttons";
+		keyup-threshold-microvolt = <3000000>;
+		poll-interval = <100>;
+
+		/*
+		 * During insertion and removal of a regular set of headphones,
+		 * i.e. one without a microphone, the voltage level briefly
+		 * dips below the 220mV of the headset connection switch.
+		 * By having a button definition with a KEY_RESERVED signal
+		 * between 0 to 220, we ensure no driver implementation thinks
+		 * that the closest thing to 0V is 220mV so clearly there must
+		 * be a headset connected.
+		 */
+
+		button-headset-disconnected {
+			label = "Headset Microphone Disconnected";
+			linux,code = <KEY_RESERVED>;
+			press-threshold-microvolt = <0>;
+		};
+
+		button-headset-connected {
+			label = "Headset Microphone Connected";
+			linux,code = <SW_MICROPHONE_INSERT>;
+			linux,input-type = <EV_SW>;
+			press-threshold-microvolt = <220000>;
+		};
+	};
+
 	vcc_12v0_dcin: regulator-vcc-12v0-dcin {
 		compatible = "regulator-fixed";
 		regulator-always-on;
@@ -639,6 +696,25 @@ hym8563: rtc@51 {
 	};
 };
 
+&i2c3 {
+	status = "okay";
+
+	es8388: audio-codec@10 {
+		compatible = "everest,es8388", "everest,es8328";
+		reg = <0x10>;
+		clocks = <&cru CLK_SAI1_MCLKOUT_TO_IO>;
+		AVDD-supply = <&vcca_3v3_s0>;
+		DVDD-supply = <&vcc_3v3_s0>;
+		HPVDD-supply = <&vcca_3v3_s0>;
+		PVDD-supply = <&vcc_3v3_s0>;
+		assigned-clocks = <&cru CLK_SAI1_MCLKOUT_TO_IO>;
+		assigned-clock-rates = <12288000>;
+		#sound-dai-cells = <0>;
+		pinctrl-names = "default";
+		pinctrl-0 = <&sai1m0_mclk>;
+	};
+};
+
 &mdio0 {
 	rgmii_phy0: ethernet-phy@1 {
 		compatible = "ethernet-phy-ieee802.3-c22";
@@ -687,6 +763,20 @@ usb_host_pwren: usb-host-pwren {
 	};
 };
 
+&sai1 {
+	pinctrl-names = "default";
+	pinctrl-0 = <&sai1m0_lrck
+		     &sai1m0_sclk
+		     &sai1m0_sdi0
+		     &sai1m0_sdo0>;
+	status = "okay";
+};
+
+&saradc {
+	vref-supply = <&vcca1v8_pldo2_s0>;
+	status = "okay";
+};
+
 &sdmmc {
 	bus-width = <4>;
 	cap-mmc-highspeed;

-- 
2.50.0

On 6/30/25 1:19 PM, Nicolas Frattaroli wrote:
> The RADXA ROCK 4D, like many other Rockchip-based boards, uses an ES8388
> analog audio codec. On the production version of the board, the codec's
> LOUT1 and ROUT1 pins are tied to the headphone jack, whereas pins LOUT2
> and ROUT2 lead to a non-populated speaker amplifier that itself leads to
> a non-populated speaker jack. The schematic is still haunted by the
> ghosts of those symbols, but it clearly marks them as "NC".
> 
> The 3.5mm TRRS jack has its microphone ring (and ground ring) wired to
> the codec's LINPUT1 and RINPUT1 pins for differential signalling.
> 
> Furthermore, it uses the SoCs ADC to detect whether the inserted cable
> is of headphones (i.e., no microphone), or a headset (i.e., with
> microphone). The way this is done is that the ADC input taps the output
> of a 100K/100K resistor divider that divides the microphone ring pin
> that's pulled up to 3.3V.
> 
> There is no ADC level difference between a completely empty jack and one
> with a set of headphones (i.e., ones that don't have a microphone)
> connected. Consequently headphone insertion detection isn't something
> that can be done.
> 
> Add the necessary codec and audio card nodes. The non-populated parts,
> i.e. LOUT2 and ROUT2, are not modeled at all, as they are not present on
> the hardware.
> 
> Also, add an adc-keys node for the headset detection, which uses an
> input type of EV_SW with the SW_MICROPHONE_INSERT keycode. Below the
> 220mV pressed voltage level of our SW_MICROPHONE_INSERT switch, we also
> define a button that emits a KEY_RESERVED code, which is there to model
> this part of the voltage range as not just being extra legroom for the
> button above it, but actually a state that is encountered in the real
> world, and should be recognised as a valid state for the ADC range to be
> in so that no "closer" ADC button is chosen.
> 
> Signed-off-by: Nicolas Frattaroli <nicolas.frattaroli@collabora.com>

Enabled CONFIG_SND_SOC_ES8328_I2C and confirm playback works fine:

    $ speaker-test -D hw:ES8388,0 -F S16_LE -c 2 -t wav

Unfortunately the recording doesn't seem to be functional:

    $ arecord -D hw:ES8388,0 -f S16_LE -c 2 -r 48000 -d 5 -V stereo /tmp/test.wav
    Recording WAVE '/tmp/test.wav' : Signed 16 bit Little Endian, Rate 48000 Hz, Stereo
                                    +00%|00%+

    $ aplay -D hw:ES8388,0 /tmp/test.wav

However, the headset plug detection works correctly:

    $ evtest
    No device specified, trying to scan all of /dev/input/event*
    Available devices:
    /dev/input/event0:	Logitech USB Receiver
    /dev/input/event1:	Logitech USB Receiver Mouse
    /dev/input/event2:	Logitech USB Receiver Consumer Control
    /dev/input/event3:	Logitech USB Receiver System Control
    /dev/input/event4:	adc-keys
    Select the device event number [0-4]: 4
    Input driver version is 1.0.1
    Input device ID: bus 0x19 vendor 0x1 product 0x1 version 0x100
    Input device name: "adc-keys"
    Supported events:
      Event type 0 (EV_SYN)
      Event type 1 (EV_KEY)
      Event type 5 (EV_SW)
        Event code 4 (SW_MICROPHONE_INSERT) state 0
    Properties:
    Testing ... (interrupt to exit)
    Event: time 1751449448.185340, type 5 (EV_SW), code 4 (SW_MICROPHONE_INSERT), value 1
    Event: time 1751449448.185340, -------------- SYN_REPORT ------------
    Event: time 1751449448.289477, type 5 (EV_SW), code 4 (SW_MICROPHONE_INSERT), value 0
    Event: time 1751449448.289477, -------------- SYN_REPORT ------------
    Event: time 1751449449.329482, type 5 (EV_SW), code 4 (SW_MICROPHONE_INSERT), value 1
    Event: time 1751449449.329482, -------------- SYN_REPORT ------------

Tested-by: Cristian Ciocaltea <cristian.ciocaltea@collabora.com>