Rockchip's UART with only RTS signal not working

Good day!

Can you tell me if UART can even work on Rockchip (especially on RK3568) processors with hardware flow control, but only using the RTS signal, without CTS?

Now I am observing the following situation when modifying the device tree when using minicom to transmit data (with hardware flow control):

  • if specify “pinctrl-0 = <&uart3m0_xfer &uart3m0_rtsn &uart3m0_ctsn>;”, then the data on TX are transmitting normally, but RTS always low, no matter how many data will be transmitted (?).
  • but if pinctrl-0 = <&uart3m0_xfer &uart3m0_rtsn>; or “pinctrl-0 = <&uart3m0_xfer>; rts-gpios = <&gpio1 RK_PA2 GPIO_ACTIVE_HIGH>;”, then there is no data on the TX line at all.
  • Using “auto-flow-control;” or “cts-override;” or “uart-has-rtscts;” does not affect behavior in any way.
device-tree part
uart0: serial@fdd50000 {
	compatible = "rockchip,rk3568-uart", "snps,dw-apb-uart";
	reg = <0x0 0xfdd50000 0x0 0x100>;
	interrupts = <GIC_SPI 116 IRQ_TYPE_LEVEL_HIGH>;
	clocks = <&pmucru SCLK_UART0>, <&pmucru PCLK_UART0>;
	clock-names = "baudclk", "apb_pclk";
	dmas = <&dmac0 0>, <&dmac0 1>;
	pinctrl-0 = <&uart0_xfer>;
	pinctrl-names = "default";
	reg-io-width = <4>;
	reg-shift = <2>;
	status = "okay";
	dma-names = "tx", "rx";
	pinctrl-0 = <&uart0_xfer &uart0_rtsn &uart0_ctsn>; // This property
	//rts-gpios = <&gpio0 RK_PC4 GPIO_ACTIVE_HIGH>; // Or this property