@@ -1,98 +0,0 @@
-* Atmel Universal Synchronous Asynchronous Receiver/Transmitter (USART)
-
-Required properties for USART:
-- compatible: Should be one of the following:
-	- "atmel,at91rm9200-usart"
-	- "atmel,at91sam9260-usart"
-	- "microchip,sam9x60-usart"
-	- "atmel,at91rm9200-dbgu", "atmel,at91rm9200-usart"
-	- "atmel,at91sam9260-dbgu", "atmel,at91sam9260-usart"
-	- "microchip,sam9x60-dbgu", "microchip,sam9x60-usart"
-- reg: Should contain registers location and length
-- interrupts: Should contain interrupt
-- clock-names: tuple listing input clock names.
-	Required elements: "usart"
-- clocks: phandles to input clocks.
-
-Required properties for USART in SPI mode:
-- #size-cells      : Must be <0>
-- #address-cells   : Must be <1>
-- cs-gpios: chipselects (internal cs not supported)
-- atmel,usart-mode : Must be <AT91_USART_MODE_SPI> (found in dt-bindings/mfd/at91-usart.h)
-
-Optional properties in serial and SPI mode:
-- dma bindings for dma transfer:
-	- dmas: DMA specifier, consisting of a phandle to DMA controller node,
-		memory peripheral interface and USART DMA channel ID, FIFO configuration.
-		The order of DMA channels is fixed. The first DMA channel must be TX
-		associated channel and the second one must be RX associated channel.
-		Refer to dma.txt and atmel-dma.txt for details.
-	- dma-names: "tx" for TX channel.
-		     "rx" for RX channel.
-		     The order of dma-names is also fixed. The first name must be "tx"
-		     and the second one must be "rx" as in the examples below.
-
-Optional properties in serial mode:
-- atmel,use-dma-rx: use of PDC or DMA for receiving data
-- atmel,use-dma-tx: use of PDC or DMA for transmitting data
-- {rts,cts,dtr,dsr,rng,dcd}-gpios: specify a GPIO for RTS/CTS/DTR/DSR/RI/DCD line respectively.
-  It will use specified PIO instead of the peripheral function pin for the USART feature.
-  If unsure, don't specify this property.
-- atmel,fifo-size: maximum number of data the RX and TX FIFOs can store for FIFO
-  capable USARTs.
-- rs485-rts-delay, rs485-rx-during-tx, linux,rs485-enabled-at-boot-time: see rs485.txt
-
-<chip> compatible description:
-- at91rm9200:  legacy USART support
-- at91sam9260: generic USART implementation for SAM9 SoCs
-
-Example:
-- use PDC:
-	usart0: serial@fff8c000 {
-		compatible = "atmel,at91sam9260-usart";
-		reg = <0xfff8c000 0x4000>;
-		interrupts = <7>;
-		clocks = <&usart0_clk>;
-		clock-names = "usart";
-		atmel,use-dma-rx;
-		atmel,use-dma-tx;
-		rts-gpios = <&pioD 15 GPIO_ACTIVE_LOW>;
-		cts-gpios = <&pioD 16 GPIO_ACTIVE_LOW>;
-		dtr-gpios = <&pioD 17 GPIO_ACTIVE_LOW>;
-		dsr-gpios = <&pioD 18 GPIO_ACTIVE_LOW>;
-		dcd-gpios = <&pioD 20 GPIO_ACTIVE_LOW>;
-		rng-gpios = <&pioD 19 GPIO_ACTIVE_LOW>;
-	};
-
-- use DMA:
-	usart0: serial@f001c000 {
-		compatible = "atmel,at91sam9260-usart";
-		reg = <0xf001c000 0x100>;
-		interrupts = <12 4 5>;
-		clocks = <&usart0_clk>;
-		clock-names = "usart";
-		atmel,use-dma-rx;
-		atmel,use-dma-tx;
-		dmas = <&dma0 2 0x3>,
-		       <&dma0 2 0x204>;
-		dma-names = "tx", "rx";
-		atmel,fifo-size = <32>;
-	};
-
-- SPI mode:
-	#include <dt-bindings/mfd/at91-usart.h>
-
-	spi0: spi@f001c000 {
-		#address-cells = <1>;
-		#size-cells = <0>;
-		compatible = "atmel,at91rm9200-usart", "atmel,at91sam9260-usart";
-		atmel,usart-mode = <AT91_USART_MODE_SPI>;
-		reg = <0xf001c000 0x100>;
-		interrupts = <12 IRQ_TYPE_LEVEL_HIGH 5>;
-		clocks = <&usart0_clk>;
-		clock-names = "usart";
-		dmas = <&dma0 2 AT91_DMA_CFG_PER_ID(3)>,
-		       <&dma0 2 (AT91_DMA_CFG_PER_ID(4) | AT91_DMA_CFG_FIFOCFG_ASAP)>;
-		dma-names = "tx", "rx";
-		cs-gpios = <&pioB 3 0>;
-	};

@@ -0,0 +1,182 @@
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+# Copyright (C) 2022 Microchip Technology, Inc. and its subsidiaries
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/serial/atmel,at91-usart.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Atmel Universal Synchronous Asynchronous Receiver/Transmitter (USART)
+
+maintainers:
+  - Richard Genoud <richard.genoud@gmail.com>
+
+properties:
+  compatible:
+    oneOf:
+      - enum:
+          - atmel,at91rm9200-usart
+          - atmel,at91sam9260-usart
+          - microchip,sam9x60-usart
+      - items:
+          - const: atmel,at91rm9200-dbgu
+          - const: atmel,at91rm9200-usart
+      - items:
+          - const: atmel,at91sam9260-dbgu
+          - const: atmel,at91sam9260-usart
+      - items:
+          - const: microchip,sam9x60-dbgu
+          - const: microchip,sam9x60-usart
+
+  reg:
+    maxItems: 1
+
+  interrupts:
+    maxItems: 1
+
+  clock-names:
+    const: usart
+
+  clocks:
+    maxItems: 1
+
+  dmas:
+    items:
+      - description: TX DMA Channel
+      - description: RX DMA Channel
+
+  dma-names:
+    items:
+      - const: tx
+      - const: rx
+
+  atmel,usart-mode:
+    $ref: /schemas/types.yaml#/definitions/uint32
+    description:
+      Must be either <AT91_USART_MODE_SPI> for SPI or
+      <AT91_USART_MODE_SERIAL> for USART (found in dt-bindings/mfd/at91-usart.h).
+    enum: [ 0, 1 ]
+
+  atmel,use-dma-rx:
+    type: boolean
+    description: use of PDC or DMA for receiving data
+
+  atmel,use-dma-tx:
+    type: boolean
+    description: use of PDC or DMA for transmitting data
+
+  atmel,fifo-size:
+    $ref: /schemas/types.yaml#/definitions/uint32
+    description:
+      Maximum number of data the RX and TX FIFOs can store for FIFO
+      capable USARTS.
+    enum: [ 16, 32 ]
+
+required:
+  - compatible
+  - reg
+  - interrupts
+  - clock-names
+  - clocks
+  - atmel,usart-mode
+
+allOf:
+  - if:
+      properties:
+        atmel,usart-mode:
+          const: 1
+    then:
+      allOf:
+        - $ref: /schemas/spi/spi-controller.yaml#
+
+      properties:
+        atmel,use-dma-rx: false
+
+        atmel,use-dma-tx: false
+
+        atmel,fifo-size: false
+
+        "#size-cells":
+          const: 0
+
+        "#address-cells":
+          const: 1
+
+      required:
+        - "#size-cells"
+        - "#address-cells"
+
+    else:
+      allOf:
+        - $ref: /schemas/serial/serial.yaml#
+        - $ref: /schemas/serial/rs485.yaml#
+
+unevaluatedProperties: false
+
+examples:
+  - |
+    #include <dt-bindings/gpio/gpio.h>
+    #include <dt-bindings/interrupt-controller/irq.h>
+    #include <dt-bindings/mfd/at91-usart.h>
+    #include <dt-bindings/dma/at91.h>
+
+    /* use PDC */
+    usart0: serial@fff8c000 {
+        compatible = "atmel,at91sam9260-usart";
+        reg = <0xfff8c000 0x4000>;
+        atmel,usart-mode = <AT91_USART_MODE_SERIAL>;
+        interrupts = <7>;
+        clocks = <&usart0_clk>;
+        clock-names = "usart";
+        atmel,use-dma-rx;
+        atmel,use-dma-tx;
+        rts-gpios = <&pioD 15 GPIO_ACTIVE_LOW>;
+        cts-gpios = <&pioD 16 GPIO_ACTIVE_LOW>;
+        dtr-gpios = <&pioD 17 GPIO_ACTIVE_LOW>;
+        dsr-gpios = <&pioD 18 GPIO_ACTIVE_LOW>;
+        dcd-gpios = <&pioD 20 GPIO_ACTIVE_LOW>;
+        rng-gpios = <&pioD 19 GPIO_ACTIVE_LOW>;
+    };
+
+  - |
+    #include <dt-bindings/gpio/gpio.h>
+    #include <dt-bindings/interrupt-controller/irq.h>
+    #include <dt-bindings/mfd/at91-usart.h>
+    #include <dt-bindings/dma/at91.h>
+
+    /* use DMA */
+    usart1: serial@f001c000 {
+        compatible = "atmel,at91sam9260-usart";
+        reg = <0xf001c000 0x100>;
+        atmel,usart-mode = <AT91_USART_MODE_SERIAL>;
+        interrupts = <12 IRQ_TYPE_LEVEL_HIGH 5>;
+        clocks = <&usart0_clk>;
+        clock-names = "usart";
+        atmel,use-dma-rx;
+        atmel,use-dma-tx;
+        dmas = <&dma0 2 AT91_DMA_CFG_PER_ID(3)>,
+               <&dma0 2 (AT91_DMA_CFG_PER_ID(4) | AT91_DMA_CFG_FIFOCFG_ASAP)>;
+        dma-names = "tx", "rx";
+        atmel,fifo-size = <32>;
+    };
+
+  - |
+    #include <dt-bindings/gpio/gpio.h>
+    #include <dt-bindings/interrupt-controller/irq.h>
+    #include <dt-bindings/mfd/at91-usart.h>
+    #include <dt-bindings/dma/at91.h>
+
+    /* SPI mode */
+    spi0: spi@f001c000 {
+        compatible = "atmel,at91sam9260-usart";
+        reg = <0xf001c000 0x100>;
+        #address-cells = <1>;
+        #size-cells = <0>;
+        atmel,usart-mode = <AT91_USART_MODE_SPI>;
+        interrupts = <12 IRQ_TYPE_LEVEL_HIGH 5>;
+        clocks = <&usart0_clk>;
+        clock-names = "usart";
+        dmas = <&dma0 2 AT91_DMA_CFG_PER_ID(3)>,
+               <&dma0 2 (AT91_DMA_CFG_PER_ID(4) | AT91_DMA_CFG_FIFOCFG_ASAP)>;
+        dma-names = "tx", "rx";
+        cs-gpios = <&pioB 3 GPIO_ACTIVE_HIGH>;
+    };