drivers: serial: add support for NS16550 RTS5817 variant

For Realtek RTS5817, RCVR fifo trigger needs to be set to 1

Signed-off-by: Darcy Lu <darcy_lu@realsil.com.cn>

Author: RtkFP

drivers/serial/Kconfig.ns16550

@@ -76,6 +76,13 @@ config UART_NS16550_TI_K3
 	  Texas Instruments K3 SoCs by enabling a vendor specific extended register
 	  set.
 
+config UART_NS16550_REALTEK_RTS5817
+	bool "Add support for NS16550 variant specific to Realtek RTS5817 SoC"
+	select PINCTRL
+	help
+	  Enabling this configuration to fix rx fifo bug of UART port in
+	  Realtek RTS5817 SoC by setting the rcvr trigger to 1.
+
 config UART_NS16550_DW8250_DW_APB
 	bool "Synopsys DesignWare 8250"
 	help

drivers/serial/uart_ns16550.c

@@ -696,6 +696,11 @@ static int uart_ns16550_configure(const struct device *dev,
 
 	ns16550_outbyte(dev_cfg, MDC(dev), mdc);
 
+#ifdef CONFIG_UART_NS16550_REALTEK_RTS5817
+	/* For RTS5817 SOC, rcvr fifo trigger needs to be set to 1 */
+	ns16550_outbyte(dev_cfg, FCR(dev),
+			FCR_FIFO | FCR_MODE0 | FCR_FIFO_1 | FCR_RCVRCLR | FCR_XMITCLR);
+#else
 	/*
 	 * Program FIFO: enabled, mode 0 (set for compatibility with quark),
 	 * generate the interrupt at 8th byte
@@ -707,6 +712,7 @@ static int uart_ns16550_configure(const struct device *dev,
 			| FCR_FIFO_64
 #endif
 			);
+#endif
 
 	if ((ns16550_inbyte(dev_cfg, IIR(dev)) & IIR_FE) == IIR_FE) {
 #ifdef CONFIG_UART_NS16550_VARIANT_NS16750

soc/realtek/fingerprint/rts5817/Kconfig.defconfig

@@ -9,4 +9,14 @@ config SYS_CLOCK_HW_CYCLES_PER_SEC
 config NUM_IRQS
 	default 32
 
+if SERIAL
+
+config UART_NS16550
+	default y
+
+config UART_NS16550_REALTEK_RTS5817
+	default y
+
+endif # SERIAL
+
 endif # SOC_SERIES_RTS5817