serial: nsl16550: add hw flow control support

keystone serial hw support hw flow control. This patch
enables hw flow control for keystone EVMs as an optional
feature based on CONFIG_SERIAL_HW_FLOW_CONTROL.

Signed-off-by: Murali Karicheri <m-karicheri2@ti.com>

README

@@ -751,6 +751,10 @@ The following options need to be configured:
 		boot loader that has already initialized the UART.  Define this
 		variable to flush the UART at init time.
 
+		CONFIG_SERIAL_HW_FLOW_CONTROL
+
+		Define this variable to enable hw flow control in serial driver.
+		Current user of this option is drivers/serial/nsl16550.c driver
 
 - Console Interface:
 		Depending on board, define exactly one serial port

drivers/serial/ns16550.c

@@ -33,6 +33,12 @@
 #if defined(CONFIG_K2HK_EVM)
 #define UART_REG_VAL_PWREMU_MGMT_UART_DISABLE   0
 #define UART_REG_VAL_PWREMU_MGMT_UART_ENABLE ((1 << 14) | (1 << 13) | (1 << 0))
+#undef UART_MCRVAL
+#ifdef CONFIG_SERIAL_HW_FLOW_CONTROL
+#define UART_MCRVAL             (UART_MCR_RTS | UART_MCR_AFE)
+#else
+#define UART_MCRVAL             (UART_MCR_RTS)
+#endif
 #endif
 
 #ifndef CONFIG_SYS_NS16550_IER

include/ns16550.h

@@ -100,6 +100,7 @@ typedef struct NS16550 *NS16550_t;
 #define UART_MCR_OUT1	0x04		/* Out 1 */
 #define UART_MCR_OUT2	0x08		/* Out 2 */
 #define UART_MCR_LOOP	0x10		/* Enable loopback test mode */
+#define UART_MCR_AFE	0x20		/* Enable auto-RTS/CTS */
 
 #define UART_MCR_DMA_EN	0x04
 #define UART_MCR_TX_DFR	0x08