linux-kernel - [PATCH 7/8] serial: fsl_lpuart: add loopback support

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Date:   Tue, 11 May 2021 22:01:47 +0200
From:   Michael Walle <michael@...le.cc>
To:     linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        Angelo Dureghello <angelo.dureghello@...esys.com>,
        Fugang Duan <fugang.duan@....com>,
        Philippe Schenker <philippe.schenker@...adex.com>,
        Michael Walle <michael@...le.cc>
Subject: [PATCH 7/8] serial: fsl_lpuart: add loopback support

The LPUART can loop the RX and TX signal. Add support for it.

Please note, this was only tested on the 32 bit version of the LPUART.

Signed-off-by: Michael Walle <michael@...le.cc>
---
 drivers/tty/serial/fsl_lpuart.c | 36 +++++++++++++++++++++++++++++++--
 1 file changed, 34 insertions(+), 2 deletions(-)

diff --git a/drivers/tty/serial/fsl_lpuart.c b/drivers/tty/serial/fsl_lpuart.c
index 19714047d571..5e66f628e895 100644
--- a/drivers/tty/serial/fsl_lpuart.c
+++ b/drivers/tty/serial/fsl_lpuart.c
@@ -1403,22 +1403,54 @@ static int lpuart32_config_rs485(struct uart_port *port,
 
 static unsigned int lpuart_get_mctrl(struct uart_port *port)
 {
-	return 0;
+	unsigned int mctrl = 0;
+	u8 reg;
+
+	reg = readb(port->membase + UARTCR1);
+	if (reg & UARTCR1_LOOPS)
+		mctrl |= TIOCM_LOOP;
+
+	return mctrl;
 }
 
 static unsigned int lpuart32_get_mctrl(struct uart_port *port)
 {
-	return 0;
+	unsigned int mctrl = 0;
+	u32 reg;
+
+	reg = lpuart32_read(port, UARTCTRL);
+	if (reg & UARTCTRL_LOOPS)
+		mctrl |= TIOCM_LOOP;
+
+	return mctrl;
 }
 
 static void lpuart_set_mctrl(struct uart_port *port, unsigned int mctrl)
 {
+	u8 reg;
+
+	reg = readb(port->membase + UARTCR1);
+
+	/* for internal loopback we need LOOPS=1 and RSRC=0 */
+	reg &= ~(UARTCR1_LOOPS | UARTCR1_RSRC);
+	if (mctrl & TIOCM_LOOP)
+		reg |= UARTCR1_LOOPS;
 
+	writeb(reg, port->membase + UARTCR1);
 }
 
 static void lpuart32_set_mctrl(struct uart_port *port, unsigned int mctrl)
 {
+	u32 reg;
+
+	reg = lpuart32_read(port, UARTCTRL);
+
+	/* for internal loopback we need LOOPS=1 and RSRC=0 */
+	reg &= ~(UARTCTRL_LOOPS | UARTCTRL_RSRC);
+	if (mctrl & TIOCM_LOOP)
+		reg |= UARTCTRL_LOOPS;
 
+	lpuart32_write(port, reg, UARTCTRL);
 }
 
 static void lpuart_break_ctl(struct uart_port *port, int break_state)
-- 
2.20.1