feat: add rockchip-uart-dma

* closes radxa-pkg#366

arch/arm64/boot/dts/rockchip/overlays/Makefile

@@ -564,7 +564,8 @@ dtb-$(CONFIG_CPU_RK3588) += \
 	rock-5t-radxa-display-10fhd.dtbo \
 	rock-5t-radxa-display-10hd.dtbo
 
-dtb-$(CONFIG_ARCH_ROCKCHIP) += rockchip-watchdog.dtbo
+dtb-$(CONFIG_ARCH_ROCKCHIP) += rockchip-watchdog.dtbo \
+	rockchip-uart-dma.dtbo
 
 dtbotxt-$(CONFIG_ARCH_ROCKCHIP) += \
 	README.overlays

arch/arm64/boot/dts/rockchip/overlays/rockchip-uart-dma.dts

@@ -0,0 +1,53 @@
+/dts-v1/;
+/plugin/;
+
+/ {
+	metadata {
+		title = "Enable DMA transfer mode for all UARTs";
+		compatible = "rockchip,rk3566", "rockchip,rk3568", "rockchip,rk3588";
+		category = "misc";
+		description = "Enable DMA transfer mode for all UARTs.
+DMA mode can help alleviating the CPU load when the data rate is high.
+It is not necessary to enable it at low data rate, as DMA requires additional resources to set up.";
+	};
+};
+
+&uart0 {
+	dma-names = "tx", "rx";
+};
+
+&uart1 {
+	dma-names = "tx", "rx";
+};
+
+&uart2 {
+	dma-names = "tx", "rx";
+};
+
+&uart3 {
+	dma-names = "tx", "rx";
+};
+
+&uart4 {
+	dma-names = "tx", "rx";
+};
+
+&uart5 {
+	dma-names = "tx", "rx";
+};
+
+&uart6 {
+	dma-names = "tx", "rx";
+};
+
+&uart7 {
+	dma-names = "tx", "rx";
+};
+
+&uart8 {
+	dma-names = "tx", "rx";
+};
+
+&uart9 {
+	dma-names = "tx", "rx";
+};