dt-bindings: iio: adc: Add ast2600-adc bindings

Add device tree bindings document for the aspeed ast2600 adc device
driver.
Signed-off-by: NBilly Tsai <billy_tsai@aspeedtech.com>
Reviewed-by: NRob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20210831071458.2334-3-billy_tsai@aspeedtech.comSigned-off-by: NJonathan Cameron <Jonathan.Cameron@huawei.com>

Documentation/devicetree/bindings/iio/adc/aspeed,ast2600-adc.yaml

+# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/iio/adc/aspeed,ast2600-adc.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: ADC that forms part of an ASPEED server management processor.
+
+maintainers:
+  - Billy Tsai <billy_tsai@aspeedtech.com>
+
+description: |
+  • 10-bits resolution for 16 voltage channels.
+  • The device split into two individual engine and each contains 8 voltage
+  channels.
+  • Channel scanning can be non-continuous.
+  • Programmable ADC clock frequency.
+  • Programmable upper and lower threshold for each channels.
+  • Interrupt when larger or less than threshold for each channels.
+  • Support hysteresis for each channels.
+  • Built-in a compensating method.
+  • Built-in a register to trim internal reference voltage.
+  • Internal or External reference voltage.
+  • Support 2 Internal reference voltage 1.2v or 2.5v.
+  • Integrate dividing circuit for battery sensing.
+
+properties:
+  compatible:
+    enum:
+      - aspeed,ast2600-adc0
+      - aspeed,ast2600-adc1
+    description:
+      Their trimming data, which is used to calibrate internal reference volage,
+      locates in different address of OTP.
+
+  reg:
+    maxItems: 1
+
+  clocks:
+    maxItems: 1
+    description:
+      Input clock used to derive the sample clock. Expected to be the
+      SoC's APB clock.
+
+  resets:
+    maxItems: 1
+
+  "#io-channel-cells":
+    const: 1
+
+  vref-supply:
+    description:
+      The external regulator supply ADC reference voltage.
+
+  aspeed,int-vref-microvolt:
+    enum: [1200000, 2500000]
+    description:
+      ADC internal reference voltage in microvolts.
+
+  aspeed,battery-sensing:
+    type: boolean
+    description:
+      Inform the driver that last channel will be used to sensor battery.
+
+  aspeed,trim-data-valid:
+    type: boolean
+    description: |
+      The ADC reference voltage can be calibrated to obtain the trimming
+      data which will be stored in otp. This property informs the driver that
+      the data store in the otp is valid.
+
+required:
+  - compatible
+  - reg
+  - clocks
+  - resets
+  - "#io-channel-cells"
+
+additionalProperties: false
+
+examples:
+  - |
+    #include <dt-bindings/clock/ast2600-clock.h>
+    adc0: adc@1e6e9000 {
+        compatible = "aspeed,ast2600-adc0";
+        reg = <0x1e6e9000 0x100>;
+        clocks = <&syscon ASPEED_CLK_APB2>;
+        resets = <&syscon ASPEED_RESET_ADC>;
+        #io-channel-cells = <1>;
+        aspeed,int-vref-microvolt = <2500000>;
+    };
+    adc1: adc@1e6e9100 {
+        compatible = "aspeed,ast2600-adc1";
+        reg = <0x1e6e9100 0x100>;
+        clocks = <&syscon ASPEED_CLK_APB2>;
+        resets = <&syscon ASPEED_RESET_ADC>;
+        #io-channel-cells = <1>;
+        aspeed,int-vref-microvolt = <2500000>;
+    };
+...