marvell: uart: a3720: Implement console_a3700_core_getc

Implementation is simple, just check if there is a pending character in
RX FIFO via RXRDY bit of Status Register and if yes, read it from
UART_RX_REG register.

Signed-off-by: Pali Rohár <pali@kernel.org>
Change-Id: I226b6e336f44f5d0ca8dcb68e49a68e8f2f49708

drivers/marvell/uart/a3700_console.S

@@ -196,14 +196,23 @@ endfunc console_a3700_putc
 	 * int console_a3700_core_getc(void)
 	 * Function to get a character from the console.
 	 * It returns the character grabbed on success
-	 * or -1 on error.
+	 * or -1 if no character is available.
 	 * In : w0 - console base address
-	 * Out : return -1 on error else return character.
+	 * Out : w0 - character if available, else -1
 	 * Clobber list : x0, x1
 	 * ---------------------------------------------
 	 */
 func console_a3700_core_getc
-	mov	w0, #-1
+	/* Check if there is a pending character */
+	ldr	w1, [x0, #UART_STATUS_REG]
+	and	w1, w1, #UARTLSR_RXRDY
+	cmp	w1, #UARTLSR_RXRDY
+	b.ne	getc_no_char
+	ldr	w0, [x0, #UART_RX_REG]
+	and	w0, w0, #0xff
+	ret
+getc_no_char:
+	mov	w0, #ERROR_NO_PENDING_CHAR
 	ret
 endfunc console_a3700_core_getc
 

include/drivers/marvell/uart/a3700_console.h

@@ -48,6 +48,7 @@
 
 /* Line Status Register bits */
 #define UARTLSR_TXFIFOFULL	(1 << 11)	/* Tx Fifo Full */
+#define UARTLSR_RXRDY		(1 << 4)	/* Rx Ready */
 
 /* UART Control Register bits */
 #define UART_CTRL_RXFIFO_RESET	(1 << 14)