drivers: ns16550: Implement RX related features

Implement ns16550_getchar() and ns16550_have_rx_data() for RX related
serial operations into ns16550 UART driver.

Signed-off-by: Alvin Chang <alvinga@andestech.com>

core/drivers/ns16550.c

@@ -43,6 +43,7 @@
 #define UART_SPR	0x7
 
 /* uart status register bits */
+#define UART_LSR_DR	0x01 /* DATA Ready */
 #define UART_LSR_THRE	0x20 /* Transmit-hold-register empty */
 
 static vaddr_t chip_to_base(struct serial_chip *chip)
@@ -73,9 +74,34 @@ static void ns16550_putc(struct serial_chip *chip, int ch)
 	serial_out(base + (UART_THR << pd->reg_shift), pd->io_width, ch);
 }
 
+static bool ns16550_have_rx_data(struct serial_chip *chip)
+{
+	struct ns16550_data *pd = container_of(chip, struct ns16550_data, chip);
+	vaddr_t base = chip_to_base(chip);
+
+	return serial_in(base + (UART_LSR << pd->reg_shift), pd->io_width) &
+	       UART_LSR_DR;
+}
+
+static int ns16550_getchar(struct serial_chip *chip)
+{
+	struct ns16550_data *pd = container_of(chip, struct ns16550_data, chip);
+	vaddr_t base = chip_to_base(chip);
+
+	while (!ns16550_have_rx_data(chip)) {
+		/* Transmit FIFO is empty, waiting again */
+		;
+	}
+
+	return serial_in(base + (UART_RBR << pd->reg_shift), pd->io_width) &
+	       0xFF;
+}
+
 static const struct serial_ops ns16550_ops = {
 	.flush = ns16550_flush,
 	.putc = ns16550_putc,
+	.getchar = ns16550_getchar,
+	.have_rx_data = ns16550_have_rx_data,
 };
 DECLARE_KEEP_PAGER(ns16550_ops);