serial: sirf: add serial loopback function support

Signed-off-by: Qipan Li <Qipan.Li@csr.com>
Signed-off-by: Barry Song <Baohua.Song@csr.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/sirfsoc_uart.c

@@ -108,6 +108,26 @@ static void sirfsoc_uart_set_mctrl(struct uart_port *port, unsigned int mctrl)
 	unsigned int val = assert ? SIRFUART_AFC_CTRL_RX_THD : 0x0;
 	unsigned int current_val;
 
+	if (mctrl & TIOCM_LOOP) {
+		if (sirfport->uart_reg->uart_type == SIRF_REAL_UART)
+			wr_regl(port, ureg->sirfsoc_line_ctrl,
+				rd_regl(port, ureg->sirfsoc_line_ctrl) |
+				SIRFUART_LOOP_BACK);
+		else
+			wr_regl(port, ureg->sirfsoc_mode1,
+				rd_regl(port, ureg->sirfsoc_mode1) |
+				SIRFSOC_USP_LOOP_BACK_CTRL);
+	} else {
+		if (sirfport->uart_reg->uart_type == SIRF_REAL_UART)
+			wr_regl(port, ureg->sirfsoc_line_ctrl,
+				rd_regl(port, ureg->sirfsoc_line_ctrl) &
+				~SIRFUART_LOOP_BACK);
+		else
+			wr_regl(port, ureg->sirfsoc_mode1,
+				rd_regl(port, ureg->sirfsoc_mode1) &
+				~SIRFSOC_USP_LOOP_BACK_CTRL);
+	}
+
 	if (!sirfport->hw_flow_ctrl || !sirfport->ms_enabled)
 		return;
 	if (sirfport->uart_reg->uart_type == SIRF_REAL_UART) {

drivers/tty/serial/sirfsoc_uart.h

@@ -322,7 +322,7 @@ struct sirfsoc_uart_register sirfsoc_uart = {
 #define SIRFSOC_USP_RX_CLK_DIVISOR_OFFSET	24
 #define SIRFSOC_USP_ASYNC_DIV2_MASK		0x3f
 #define SIRFSOC_USP_ASYNC_DIV2_OFFSET		16
-
+#define SIRFSOC_USP_LOOP_BACK_CTRL		BIT(2)
 /* USP-UART Common */
 #define SIRFSOC_UART_RX_TIMEOUT(br, to)	(((br) * (((to) + 999) / 1000)) / 1000)
 #define SIRFUART_RECV_TIMEOUT_VALUE(x)	\