linux-kernel - [PATCH 09/10] USB: serial: xr: fix pin configuration

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Date:   Thu, 21 Jan 2021 11:29:21 +0100
From:   Johan Hovold <johan@...nel.org>
To:     linux-usb@...r.kernel.org
Cc:     Manivannan Sadhasivam <mani@...nel.org>,
        linux-kernel@...r.kernel.org, Johan Hovold <johan@...nel.org>
Subject: [PATCH 09/10] USB: serial: xr: fix pin configuration

Make sure that the modem pins are set up correctly when opening the
port to avoid leaving, for example, DTR and RTS configured as inputs,
which is the device default.

This is specifically needed to be able to control DTR and RTS when
hardware flow control is disabled.

Fixes: a8f54b7bd132 ("USB: serial: add MaxLinear/Exar USB to Serial driver")
Signed-off-by: Johan Hovold <johan@...nel.org>
---
 drivers/usb/serial/xr_serial.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/usb/serial/xr_serial.c b/drivers/usb/serial/xr_serial.c
index 183731cd2ef7..f67e7dba9509 100644
--- a/drivers/usb/serial/xr_serial.c
+++ b/drivers/usb/serial/xr_serial.c
@@ -502,6 +502,7 @@ static void xr_set_termios(struct tty_struct *tty,
 
 static int xr_open(struct tty_struct *tty, struct usb_serial_port *port)
 {
+	u8 gpio_dir;
 	int ret;
 
 	ret = xr_uart_enable(port);
@@ -510,6 +511,13 @@ static int xr_open(struct tty_struct *tty, struct usb_serial_port *port)
 		return ret;
 	}
 
+	/*
+	 * Configure DTR and RTS as outputs and RI, CD, DSR and CTS as
+	 * inputs.
+	 */
+	gpio_dir = XR21V141X_UART_MODE_DTR | XR21V141X_UART_MODE_RTS;
+	xr_set_reg_uart(port, XR21V141X_REG_GPIO_DIR, gpio_dir);
+
 	/* Setup termios */
 	if (tty)
 		xr_set_termios(tty, port, NULL);
-- 
2.26.2