ASoC: dt-bindings: add ESS Technology ES9039Q2M

Add a binding for the ES9039Q2M, a 32-bit two-channel audio DAC with an
asynchronous sample rate converter.

The part selects between two control personalities with its MODE pin:
hardware mode, strapped by HW0/HW1/HW2 with no control bus at all, and
software mode over I2C or SPI. This binding describes software mode over
I2C, which MODE = GND selects.

The four supply inputs are described and required. DVDD is not among
them: the part's 1.2V digital rail is generated on chip and the pin
takes only a decoupling capacitor. The datasheet asks for the supplies
in a set order - AVDD, then VCCA about 200us later, then the two
output-stage references, and the reverse on the way down - which the
description records, so a board with separately switchable rails has
it to hand.

Assisted-by: Claude:claude-opus-5
Signed-off-by: Karl Asseily <karl@asseily.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@oss.qualcomm.com>
Link: https://patch.msgid.link/20260918182317.143223-3-karl@asseily.com
Signed-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/sound/esstech,es9039q2m.yaml

@@ -0,0 +1,94 @@
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/sound/esstech,es9039q2m.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: ESS Technology ES9039Q2M audio DAC
+
+maintainers:
+  - Karl Asseily <karl@asseily.com>
+
+description:
+  The ES9039Q2M is a 32-bit two-channel audio DAC supporting PCM to 768 kHz,
+  DSD64 to DSD1024, DoP and S/PDIF. It is controlled over I2C or SPI when the
+  MODE pin selects software mode; this binding covers the I2C interface. The
+  part contains an asynchronous sample rate converter, so the system clock need
+  not be synchronous with the audio bit or frame clocks.
+
+  The four supplies are all nominally 3.3V and the datasheet requires a set
+  order - AVDD first, then VCCA about 200us later, then AVCC_DAC1 and
+  AVCC_DAC2, and the reverse on the way down. DVDD, the part's 1.2V rail, is
+  on-chip and needs only its decoupling capacitor - it is not a supply input
+  and has no property here.
+
+allOf:
+  - $ref: dai-common.yaml#
+
+properties:
+  compatible:
+    const: esstech,es9039q2m
+
+  reg:
+    description:
+      I2C address, selected by the ADDR0 and ADDR1 pins - 0x48, 0x49, 0x4a or
+      0x4b for GND/GND, GND/AVDD, AVDD/GND and AVDD/AVDD respectively.
+    enum: [ 0x48, 0x49, 0x4a, 0x4b ]
+
+  clocks:
+    maxItems: 1
+
+  clock-names:
+    const: mclk
+
+  avdd-supply:
+    description:
+      3.3V supply for the part's internal digital regulator, pin AVDD. It is
+      the first rail up and the last down, per the ordering described above.
+
+  vcca-supply:
+    description: 3.3V analogue supply, pin VCCA.
+
+  avcc-dac1-supply:
+    description:
+      3.3V reference supply for the channel 1 analogue output stage, pin
+      AVCC_DAC1. The datasheet allows this rail to move by up to 15% where a
+      calibrating regulator tracks the DAC's output impedance.
+
+  avcc-dac2-supply:
+    description:
+      3.3V reference supply for the channel 2 analogue output stage, pin
+      AVCC_DAC2, with the same 15% allowance as channel 1.
+
+  "#sound-dai-cells":
+    const: 0
+
+required:
+  - compatible
+  - reg
+  - avdd-supply
+  - vcca-supply
+  - avcc-dac1-supply
+  - avcc-dac2-supply
+  - "#sound-dai-cells"
+
+unevaluatedProperties: false
+
+examples:
+  - |
+    i2c {
+        #address-cells = <1>;
+        #size-cells = <0>;
+
+        audio-codec@48 {
+            compatible = "esstech,es9039q2m";
+            reg = <0x48>;
+            #sound-dai-cells = <0>;
+            clocks = <&dac_mclk>;
+            clock-names = "mclk";
+            avdd-supply = <&dac_3v3>;
+            vcca-supply = <&dac_3v3>;
+            avcc-dac1-supply = <&dac_avcc1>;
+            avcc-dac2-supply = <&dac_avcc2>;
+        };
+    };