bindings: iio: adc: Add bindings for TI ADS131M0x ADCs

Add device tree bindings documentation for the Texas Instruments
ADS131M0x analog-to-digital converters. This family includes the ADS131M02,
ADS131M03, ADS131M04, ADS131M06, and ADS131M08 variants.

These variants differ primarily in the number of supported channels
(2, 3, 4, 6, and 8, respectively), which requires separate compatible
strings to validate the channel nodes.

Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Reviewed-by: David Lechner <dlechner@baylibre.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

diff --git a/Documentation/devicetree/bindings/iio/adc/ti,ads131m02.yaml b/Documentation/devicetree/bindings/iio/adc/ti,ads131m02.yaml
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+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/iio/adc/ti,ads131m02.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Texas Instruments ADS131M0x 2-, 3-, 4-, 6- and 8-Channel ADCs
+
+maintainers:
+  - Oleksij Rempel <o.rempel@pengutronix.de>
+
+description: |
+  The ADS131M0x are a family of multichannel, simultaneous sampling,
+  24-bit, delta-sigma, analog-to-digital converters (ADCs) with a
+  built-in programmable gain amplifier (PGA) and internal reference.
+  Communication with the ADC chip is via SPI.
+
+  Datasheets:
+  - ADS131M02: https://www.ti.com/lit/ds/symlink/ads131m02.pdf
+  - ADS131M03: https://www.ti.com/lit/ds/symlink/ads131m03.pdf
+  - ADS131M04: https://www.ti.com/lit/ds/symlink/ads131m04.pdf
+  - ADS131M06: https://www.ti.com/lit/ds/symlink/ads131m06.pdf
+  - ADS131M08: https://www.ti.com/lit/ds/symlink/ads131m08.pdf
+
+properties:
+  compatible:
+    enum:
+      - ti,ads131m02
+      - ti,ads131m03
+      - ti,ads131m04
+      - ti,ads131m06
+      - ti,ads131m08
+
+  reg:
+    description: SPI chip select number.
+
+  clocks:
+    description:
+      Phandle to the external clock source required by the ADC's CLKIN pin.
+      The datasheet recommends specific frequencies based on the desired power
+      mode (e.g., 8.192 MHz for High-Resolution mode).
+    maxItems: 1
+
+  avdd-supply:
+    description: Analog power supply (AVDD).
+
+  dvdd-supply:
+    description: Digital power supply (DVDD).
+
+  interrupts:
+    description: DRDY (Data Ready) output signal.
+    maxItems: 1
+
+  reset-gpios:
+    description: Optional RESET signal.
+    maxItems: 1
+
+  clock-names:
+    description:
+      Indicates if a crystal oscillator (XTAL) or CMOS signal is connected
+      (CLKIN). Note that XTAL mode is only supported on ADS131M06 and ADS131M08.
+    enum: [xtal, clkin]
+
+  refin-supply:
+    description: Optional external reference supply (REFIN).
+
+  '#address-cells':
+    const: 1
+
+  '#size-cells':
+    const: 0
+
+required:
+  - compatible
+  - reg
+  - clocks
+  - clock-names
+  - avdd-supply
+  - dvdd-supply
+
+patternProperties:
+  "^channel@[0-7]$":
+    type: object
+    $ref: /schemas/iio/adc/adc.yaml#
+    description: Properties for a single ADC channel.
+
+    properties:
+      reg:
+        description: The channel index (0-7).
+        minimum: 0
+        maximum: 7  # Max channels on ADS131M08
+
+      label: true
+
+    required:
+      - reg
+
+    unevaluatedProperties: false
+
+allOf:
+  - $ref: /schemas/spi/spi-peripheral-props.yaml#
+
+  - if:
+      # 20-pin devices: M02, M03, M04
+      # These do not support XTAL or REFIN.
+      properties:
+        compatible:
+          enum:
+            - ti,ads131m02
+            - ti,ads131m03
+            - ti,ads131m04
+    then:
+      properties:
+        clock-names:
+          const: clkin
+        refin-supply: false
+
+  - if:
+      # ADS131M02: 2 channels max (0-1)
+      properties:
+        compatible:
+          contains:
+            const: ti,ads131m02
+    then:
+      patternProperties:
+        "^channel@[0-1]$":
+          properties:
+            reg:
+              maximum: 1
+        "^channel@[2-7]$": false
+
+  - if:
+      # ADS131M03: 3 channels max (0-2)
+      properties:
+        compatible:
+          contains:
+            const: ti,ads131m03
+    then:
+      patternProperties:
+        "^channel@[0-2]$":
+          properties:
+            reg:
+              maximum: 2
+        "^channel@[3-7]$": false
+
+  - if:
+      # ADS131M04: 4 channels max (0-3)
+      properties:
+        compatible:
+          contains:
+            const: ti,ads131m04
+    then:
+      patternProperties:
+        "^channel@[0-3]$":
+          properties:
+            reg:
+              maximum: 3
+        "^channel@[4-7]$": false
+
+  - if:
+      # ADS131M06: 6 channels max (0-5)
+      properties:
+        compatible:
+          contains:
+            const: ti,ads131m06
+    then:
+      patternProperties:
+        "^channel@[0-5]$":
+          properties:
+            reg:
+              maximum: 5
+        "^channel@[6-7]$": false
+
+unevaluatedProperties: false
+
+examples:
+  - |
+    #include <dt-bindings/clock/stm32mp1-clks.h>
+
+    spi1 {
+        #address-cells = <1>;
+        #size-cells = <0>;
+
+        adc@0 {
+            compatible = "ti,ads131m02";
+            reg = <0>;
+            spi-max-frequency = <8000000>;
+
+            clocks = <&rcc CK_MCO2>;
+            clock-names = "clkin";
+
+            avdd-supply = <&vdd_ana>;
+            dvdd-supply = <&vdd_dig>;
+
+            #address-cells = <1>;
+            #size-cells = <0>;
+
+            channel@0 {
+                reg = <0>;
+                label = "input_voltage";
+            };
+
+            channel@1 {
+                reg = <1>;
+                label = "input_current";
+            };
+        };
+    };