overlays: Add uart0 overlay to change pin usage

Signed-off-by: Phil Elwell <phil@raspberrypi.org>

arch/arm/boot/dts/overlays/Makefile

@@ -117,6 +117,7 @@ dtbo-$(CONFIG_ARCH_BCM2835) += \
 	spi2-2cs.dtbo \
 	spi2-3cs.dtbo \
 	tinylcd35.dtbo \
+	uart0.dtbo \
 	uart1.dtbo \
 	vc4-fkms-v3d.dtbo \
 	vc4-kms-v3d.dtbo \

arch/arm/boot/dts/overlays/README

@@ -1671,8 +1671,19 @@ Params: speed                   Display SPI bus speed
                 dtoverlay=tinylcd35,touch,touchgpio=3
 
 
+Name:   uart0
+Info:   Change the pin usage of uart0
+Load:   dtoverlay=uart0,<param>=<val>
+Params: txd0_pin                GPIO pin for TXD0 (14, 32 or 36 - default 14)
+
+        rxd0_pin                GPIO pin for RXD0 (15, 33 or 37 - default 15)
+
+        pin_func                Alternative pin function - 4(Alt0) for 14&15,
+                                7(Alt3) for 32&33, 6(Alt2) for 36&37
+
+
 Name:   uart1
-Info:   Enable uart1 in place of uart0
+Info:   Change the pin usage of uart1
 Load:   dtoverlay=uart1,<param>=<val>
 Params: txd1_pin                GPIO pin for TXD1 (14, 32 or 40 - default 14)
 

arch/arm/boot/dts/overlays/uart0-overlay.dts

@@ -0,0 +1,32 @@
+/dts-v1/;
+/plugin/;
+
+/{
+	compatible = "brcm,bcm2708";
+
+	fragment@0 {
+		target = <&uart0>;
+		__overlay__ {
+			pinctrl-names = "default";
+			pinctrl-0 = <&uart0_pins>;
+			status = "okay";
+		};
+	};
+
+	fragment@1 {
+		target = <&gpio>;
+		__overlay__ {
+			uart0_pins: uart0_pins {
+				brcm,pins = <14 15>;
+				brcm,function = <4>; /* alt0 */
+				brcm,pull = <0 2>;
+			};
+		};
+	};
+
+	__overrides__ {
+		txd0_pin = <&uart0_pins>,"brcm,pins:0";
+		rxd0_pin = <&uart0_pins>,"brcm,pins:4";
+		pin_func = <&uart0_pins>,"brcm,function:0";
+	};
+};