Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
From:   mani@kernel.org
To:     johan@kernel.org, gregkh@linuxfoundation.org
Cc:     linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org,
        patong.mxl@gmail.com, Manivannan Sadhasivam <mani@kernel.org>
Subject: [PATCH v3 1/2] usb: serial: Add MaxLinear/Exar USB to Serial driver
Date:   Fri,  1 May 2020 00:19:23 +0530
Message-Id: <20200430184924.31690-2-mani@kernel.org>
In-Reply-To: <20200430184924.31690-1-mani@kernel.org>
References: <20200430184924.31690-1-mani@kernel.org>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

From: Manivannan Sadhasivam <mani@kernel.org>

Add support for MaxLinear/Exar USB to Serial converters. This driver
only supports XR21V141X series but it can be extended to other series
from Exar as well in future.

This driver is inspired from the initial one submitted by Patong Yang:

https://patchwork.kernel.org/patch/10543261/

While the initial driver was a custom tty USB driver exposing whole
new serial interface ttyXRUSBn, this version is completely based on USB
serial core thus exposing the interfaces as ttyUSBn. This will avoid
the overhead of exposing a new USB serial interface which the userspace
tools are unaware of.

Signed-off-by: Manivannan Sadhasivam <mani@kernel.org>
---
 drivers/usb/serial/Kconfig     |   9 +
 drivers/usb/serial/Makefile    |   1 +
 drivers/usb/serial/xr_serial.c | 624 +++++++++++++++++++++++++++++++++
 3 files changed, 634 insertions(+)
 create mode 100644 drivers/usb/serial/xr_serial.c

diff --git a/drivers/usb/serial/Kconfig b/drivers/usb/serial/Kconfig
index 25d7e0c36d38..8f6ad9f94735 100644
--- a/drivers/usb/serial/Kconfig
+++ b/drivers/usb/serial/Kconfig
@@ -644,6 +644,15 @@ config USB_SERIAL_UPD78F0730
 	  To compile this driver as a module, choose M here: the
 	  module will be called upd78f0730.
 
+config USB_SERIAL_XR
+	tristate "USB MaxLinear/Exar USB to Serial driver"
+	help
+	  Say Y here if you want to use MaxLinear/Exar USB to Serial converter
+	  devices.
+
+	  To compile this driver as a module, choose M here: the
+	  module will be called xr_serial.
+
 config USB_SERIAL_DEBUG
 	tristate "USB Debugging Device"
 	help
diff --git a/drivers/usb/serial/Makefile b/drivers/usb/serial/Makefile
index 2d491e434f11..4f69c2a3aff3 100644
--- a/drivers/usb/serial/Makefile
+++ b/drivers/usb/serial/Makefile
@@ -62,4 +62,5 @@ obj-$(CONFIG_USB_SERIAL_VISOR)			+= visor.o
 obj-$(CONFIG_USB_SERIAL_WISHBONE)		+= wishbone-serial.o
 obj-$(CONFIG_USB_SERIAL_WHITEHEAT)		+= whiteheat.o
 obj-$(CONFIG_USB_SERIAL_XIRCOM)			+= keyspan_pda.o
+obj-$(CONFIG_USB_SERIAL_XR)			+= xr_serial.o
 obj-$(CONFIG_USB_SERIAL_XSENS_MT)		+= xsens_mt.o
diff --git a/drivers/usb/serial/xr_serial.c b/drivers/usb/serial/xr_serial.c
new file mode 100644
index 000000000000..fdb9ddf8bd95
--- /dev/null
+++ b/drivers/usb/serial/xr_serial.c
@@ -0,0 +1,624 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * MaxLinear/Exar USB to Serial driver
+ *
+ * Based on initial driver written by Patong Yang <patong.mxl@gmail.com>
+ *
+ * Copyright (c) 2020 Manivannan Sadhasivam <mani@kernel.org>
+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/tty.h>
+#include <linux/usb.h>
+#include <linux/usb/serial.h>
+
+struct xr_uart_regs {
+	u8 enable;
+	u8 format;
+	u8 flow_ctrl;
+	u8 xon_char;
+	u8 xoff_char;
+	u8 loopback;
+	u8 tx_break;
+	u8 rs485_delay;
+	u8 gpio_mode;
+	u8 gpio_dir;
+	u8 gpio_int_mask;
+	u8 gpio_set;
+	u8 gpio_clr;
+	u8 gpio_status;
+};
+
+struct xr_port_private {
+	const struct xr_uart_regs *regs;
+};
+
+struct xr_txrx_clk_mask {
+	u16 tx;
+	u16 rx0;
+	u16 rx1;
+};
+
+#define XR21V141X_ID			0x1410
+#define XR_INT_OSC_HZ			48000000
+
+/* USB Requests */
+#define XR_SET_XR21V141X		0
+#define XR_GET_XR21V141X		1
+
+#define XR21V141X_CLOCK_DIVISOR_0	0x4
+#define XR21V141X_CLOCK_DIVISOR_1	0x5
+#define XR21V141X_CLOCK_DIVISOR_2	0x6
+#define XR21V141X_TX_CLOCK_MASK_0	0x7
+#define XR21V141X_TX_CLOCK_MASK_1	0x8
+#define XR21V141X_RX_CLOCK_MASK_0	0x9
+#define XR21V141X_RX_CLOCK_MASK_1	0xa
+
+/* XR21V141X register blocks */
+#define XR21V141X_UART_REG_BLOCK	0
+#define XR21V141X_URM_REG_BLOCK		4
+#define XR21V141X_UART_CUSTOM_BLOCK	0x66
+
+/* XR21V141X UART Manager Registers */
+#define XR21V141X_URM_FIFO_ENABLE_REG	0x10
+#define XR21V141X_URM_ENABLE_TX_FIFO	0x1
+#define XR21V141X_URM_ENABLE_RX_FIFO	0x2
+
+#define XR21V141X_URM_RX_FIFO_RESET	0x18
+#define XR21V141X_URM_TX_FIFO_RESET	0x1c
+
+#define UART_ENABLE_TX			0x1
+#define UART_ENABLE_RX			0x2
+
+#define UART_MODE_RI			BIT(0)
+#define UART_MODE_CD			BIT(1)
+#define UART_MODE_DSR			BIT(2)
+#define UART_MODE_DTR			BIT(3)
+#define UART_MODE_CTS			BIT(4)
+#define UART_MODE_RTS			BIT(5)
+
+#define UART_BREAK_ON			0xff
+#define UART_BREAK_OFF			0
+
+#define UART_DATA_MASK			GENMASK(3, 0)
+#define UART_DATA_7			0x7
+#define UART_DATA_8			0x8
+
+#define UART_PARITY_MASK		GENMASK(6, 4)
+#define UART_PARITY_SHIFT		0x4
+#define UART_PARITY_NONE		0x0
+#define UART_PARITY_ODD			0x1
+#define UART_PARITY_EVEN		0x2
+#define UART_PARITY_MARK		0x3
+#define UART_PARITY_SPACE		0x4
+
+#define UART_STOP_MASK			BIT(7)
+#define UART_STOP_SHIFT			0x7
+#define UART_STOP_1			0x0
+#define UART_STOP_2			0x1
+
+#define UART_FLOW_MODE_NONE		0x0
+#define UART_FLOW_MODE_HW		0x1
+#define UART_FLOW_MODE_SW		0x2
+
+#define UART_MODE_GPIO			0x0
+#define UART_MODE_RTS_CTS		0x1
+#define UART_MODE_DTR_DSR		0x2
+#define UART_MODE_RS485			0x3
+#define UART_MODE_RS485_ADDR		0x4
+
+static const struct xr_uart_regs xr21v141x_regs = {
+	.enable = 0x03,
+	.format = 0x0b,
+	.flow_ctrl = 0x0c,
+	.xon_char = 0x10,
+	.xoff_char = 0x11,
+	.loopback = 0x12,
+	.tx_break = 0x14,
+	.rs485_delay = 0x15,
+	.gpio_mode = 0x1a,
+	.gpio_dir = 0x1b,
+	.gpio_int_mask = 0x1c,
+	.gpio_set = 0x1d,
+	.gpio_clr = 0x1e,
+	.gpio_status = 0x1f,
+};
+
+static int xr_set_reg(struct usb_serial_port *port, u8 block, u8 reg,
+		      u8 val)
+{
+	struct usb_serial *serial = port->serial;
+	int ret = -EINVAL;
+
+	/* XR21V141X uses custom command for writing UART registers */
+	ret = usb_control_msg(serial->dev,
+			      usb_sndctrlpipe(serial->dev, 0),
+			      XR_SET_XR21V141X,
+			      USB_DIR_OUT | USB_TYPE_VENDOR, val,
+			      reg | (block << 8), NULL, 0,
+			      USB_CTRL_SET_TIMEOUT);
+
+	if (ret < 0)
+		dev_err(&port->dev, "Failed to set reg 0x%x status: %d\n",
+			reg, ret);
+
+	return ret;
+}
+
+static int xr_get_reg(struct usb_serial_port *port, u8 block, u8 reg,
+		      u8 *val)
+{
+	struct usb_serial *serial = port->serial;
+	void *dmabuf;
+	int ret = -EINVAL;
+
+	dmabuf = kmalloc(1, GFP_KERNEL);
+	if (!dmabuf)
+		return -ENOMEM;
+
+	/* XR21V141X uses custom command for reading UART registers */
+	ret = usb_control_msg(serial->dev,
+			      usb_rcvctrlpipe(serial->dev, 0),
+			      XR_GET_XR21V141X,
+			      USB_DIR_IN | USB_TYPE_VENDOR, 0,
+			      reg | (block << 8), dmabuf, 1,
+			      USB_CTRL_SET_TIMEOUT);
+
+	if (ret == 1) {
+		memcpy(val, dmabuf, 1);
+		ret = 0;
+	} else {
+		dev_err(&port->dev, "Failed to get reg 0x%x status: %d\n",
+			reg, ret);
+		if (ret >= 0)
+			ret = -EIO;
+	}
+
+	kfree(dmabuf);
+
+	return ret;
+}
+
+/* Tx and Rx clock mask values obtained from section 3.3.4 of datasheet */
+static const struct xr_txrx_clk_mask xr21v141x_txrx_clk_masks[] = {
+	{ 0x000, 0x000, 0x000 },
+	{ 0x000, 0x000, 0x000 },
+	{ 0x100, 0x000, 0x100 },
+	{ 0x020, 0x400, 0x020 },
+	{ 0x010, 0x100, 0x010 },
+	{ 0x208, 0x040, 0x208 },
+	{ 0x104, 0x820, 0x108 },
+	{ 0x844, 0x210, 0x884 },
+	{ 0x444, 0x110, 0x444 },
+	{ 0x122, 0x888, 0x224 },
+	{ 0x912, 0x448, 0x924 },
+	{ 0x492, 0x248, 0x492 },
+	{ 0x252, 0x928, 0x292 },
+	{ 0x94a, 0x4a4, 0xa52 },
+	{ 0x52a, 0xaa4, 0x54a },
+	{ 0xaaa, 0x954, 0x4aa },
+	{ 0xaaa, 0x554, 0xaaa },
+	{ 0x555, 0xad4, 0x5aa },
+	{ 0xb55, 0xab4, 0x55a },
+	{ 0x6b5, 0x5ac, 0xb56 },
+	{ 0x5b5, 0xd6c, 0x6d6 },
+	{ 0xb6d, 0xb6a, 0xdb6 },
+	{ 0x76d, 0x6da, 0xbb6 },
+	{ 0xedd, 0xdda, 0x76e },
+	{ 0xddd, 0xbba, 0xeee },
+	{ 0x7bb, 0xf7a, 0xdde },
+	{ 0xf7b, 0xef6, 0x7de },
+	{ 0xdf7, 0xbf6, 0xf7e },
+	{ 0x7f7, 0xfee, 0xefe },
+	{ 0xfdf, 0xfbe, 0x7fe },
+	{ 0xf7f, 0xefe, 0xffe },
+	{ 0xfff, 0xffe, 0xffd },
+};
+
+static int xr_set_baudrate(struct tty_struct *tty,
+			   struct usb_serial_port *port)
+{
+	u32 divisor = XR_INT_OSC_HZ / tty->termios.c_ospeed;
+	u32 idx = (32 * divisor) & 0x1f;
+	u16 tx_mask = xr21v141x_txrx_clk_masks[idx].tx;
+	u16 rx_mask = (divisor & 1) ? xr21v141x_txrx_clk_masks[idx].rx1 :
+				      xr21v141x_txrx_clk_masks[idx].rx0;
+	int ret;
+
+	dev_dbg(&port->dev, "Setting baud rate :%u\n", tty->termios.c_ospeed);
+
+	/*
+	 * XR21V141X uses fractional baud rate generator with 48MHz internal
+	 * oscillator and 19-bit programmable divisor. So theoretically it can
+	 * generate most commonly used baud rates with high accuracy.
+	 */
+	ret = xr_set_reg(port, XR21V141X_UART_REG_BLOCK,
+			 XR21V141X_CLOCK_DIVISOR_0, (divisor & 0xff));
+	if (ret)
+		return ret;
+
+	ret = xr_set_reg(port, XR21V141X_UART_REG_BLOCK,
+			 XR21V141X_CLOCK_DIVISOR_1, ((divisor >>  8) & 0xff));
+	if (ret)
+		return ret;
+
+	ret = xr_set_reg(port, XR21V141X_UART_REG_BLOCK,
+			 XR21V141X_CLOCK_DIVISOR_2, ((divisor >> 16) & 0xff));
+	if (ret)
+		return ret;
+
+	ret = xr_set_reg(port, XR21V141X_UART_REG_BLOCK,
+			 XR21V141X_TX_CLOCK_MASK_0, (tx_mask & 0xff));
+	if (ret)
+		return ret;
+
+	ret = xr_set_reg(port, XR21V141X_UART_REG_BLOCK,
+			 XR21V141X_TX_CLOCK_MASK_1, ((tx_mask >>  8) & 0xff));
+	if (ret)
+		return ret;
+
+	ret = xr_set_reg(port, XR21V141X_UART_REG_BLOCK,
+			 XR21V141X_RX_CLOCK_MASK_0, (rx_mask & 0xff));
+	if (ret)
+		return ret;
+
+	ret = xr_set_reg(port, XR21V141X_UART_REG_BLOCK,
+			 XR21V141X_RX_CLOCK_MASK_1, ((rx_mask >>  8) & 0xff));
+
+	return ret;
+}
+
+/*
+ * According to datasheet, below is the recommended sequence for enabling UART
+ * module in XR21V141X:
+ *
+ * Enable Tx FIFO
+ * Enable Tx and Rx
+ * Enable Rx FIFO
+ */
+static int xr_uart_enable(struct usb_serial_port *port)
+{
+	struct xr_port_private *port_priv = usb_get_serial_port_data(port);
+	int ret;
+
+	ret = xr_set_reg(port, XR21V141X_URM_REG_BLOCK,
+			 XR21V141X_URM_FIFO_ENABLE_REG,
+			 XR21V141X_URM_ENABLE_TX_FIFO);
+	if (ret)
+		return ret;
+
+	ret = xr_set_reg(port, XR21V141X_UART_REG_BLOCK,
+			 port_priv->regs->enable,
+			 UART_ENABLE_TX | UART_ENABLE_RX);
+	if (ret)
+		return ret;
+
+	ret = xr_set_reg(port, XR21V141X_URM_REG_BLOCK,
+			 XR21V141X_URM_FIFO_ENABLE_REG,
+			 XR21V141X_URM_ENABLE_TX_FIFO |
+			 XR21V141X_URM_ENABLE_RX_FIFO);
+
+	return ret;
+}
+
+static int xr_uart_disable(struct usb_serial_port *port)
+{
+	struct xr_port_private *port_priv = usb_get_serial_port_data(port);
+	int ret;
+
+	ret = xr_set_reg(port, XR21V141X_UART_REG_BLOCK,
+			 port_priv->regs->enable, 0);
+	if (ret)
+		return ret;
+
+	ret = xr_set_reg(port, XR21V141X_URM_REG_BLOCK,
+			 XR21V141X_URM_FIFO_ENABLE_REG, 0);
+
+	return ret;
+}
+
+static int xr_open(struct tty_struct *tty, struct usb_serial_port *port)
+{
+	int ret;
+
+	ret = xr_uart_enable(port);
+	if (ret) {
+		dev_err(&port->dev, "Failed to enable UART\n");
+		return ret;
+	}
+
+	ret = xr_set_baudrate(tty, port);
+	if (ret) {
+		dev_err(&port->dev, "Failed to set baudrate\n");
+		return ret;
+	}
+
+	return usb_serial_generic_open(tty, port);
+}
+
+static void xr_close(struct usb_serial_port *port)
+{
+	usb_serial_generic_close(port);
+
+	xr_uart_disable(port);
+}
+
+static void xr_set_flow_mode(struct tty_struct *tty,
+			     struct usb_serial_port *port,
+			     unsigned int cflag)
+{
+	struct xr_port_private *port_priv = usb_get_serial_port_data(port);
+	u8 flow, gpio_mode;
+	int ret;
+
+	ret = xr_get_reg(port, XR21V141X_UART_REG_BLOCK,
+			 port_priv->regs->gpio_mode, &gpio_mode);
+	if (ret)
+		return;
+
+	if (cflag & CRTSCTS) {
+		dev_dbg(&port->dev, "Enabling hardware flow ctrl\n");
+		flow = UART_FLOW_MODE_HW;
+		gpio_mode |= UART_MODE_RTS_CTS;
+	} else if (I_IXOFF(tty) || I_IXON(tty)) {
+		u8 start_char = START_CHAR(tty);
+		u8 stop_char = STOP_CHAR(tty);
+
+		dev_dbg(&port->dev, "Enabling sw flow ctrl\n");
+		flow = UART_FLOW_MODE_SW;
+		gpio_mode |= UART_MODE_GPIO;
+
+		xr_set_reg(port, XR21V141X_UART_REG_BLOCK,
+			   port_priv->regs->xon_char, start_char);
+		xr_set_reg(port, XR21V141X_UART_REG_BLOCK,
+			   port_priv->regs->xoff_char, stop_char);
+	} else {
+		dev_dbg(&port->dev, "No flow ctrl\n");
+		flow = UART_FLOW_MODE_NONE;
+	}
+
+	ret = xr_set_reg(port, XR21V141X_UART_REG_BLOCK,
+			 port_priv->regs->flow_ctrl, flow);
+	if (ret)
+		return;
+
+	xr_set_reg(port, XR21V141X_UART_REG_BLOCK, port_priv->regs->gpio_mode,
+		   gpio_mode);
+}
+
+static void xr_set_termios(struct tty_struct *tty,
+			   struct usb_serial_port *port,
+			   struct ktermios *old_termios)
+{
+	struct xr_port_private *port_priv = usb_get_serial_port_data(port);
+	struct device *dev = &port->dev;
+	unsigned int cflag, old_cflag;
+	int ret;
+	u8 bits;
+
+	cflag = tty->termios.c_cflag;
+	old_cflag = old_termios->c_cflag;
+
+	if (tty->termios.c_ospeed != old_termios->c_ospeed)
+		xr_set_baudrate(tty, port);
+
+	ret = xr_get_reg(port, XR21V141X_UART_REG_BLOCK,
+			 port_priv->regs->format, &bits);
+	if (ret)
+		return;
+
+	/* If the number of data bits is to be updated */
+	if ((cflag & CSIZE) != (old_cflag & CSIZE)) {
+		bits &= ~UART_DATA_MASK;
+		switch (cflag & CSIZE) {
+		case CS7:
+			bits |= UART_DATA_7;
+			dev_dbg(dev, "Setting data bits: 7\n");
+			break;
+		case CS8:
+		/* CS9 not supported */
+		default:
+			bits |= UART_DATA_8;
+			dev_dbg(dev, "Setting data bits: 8\n");
+			break;
+		}
+	}
+
+	if ((cflag & (PARENB | PARODD | CMSPAR)) !=
+	    (old_cflag & (PARENB | PARODD | CMSPAR))) {
+		bits &= ~UART_PARITY_MASK;
+		if (cflag & PARENB) {
+			if (cflag & CMSPAR) {
+				if (cflag & PARODD) {
+					bits |= (UART_PARITY_MARK <<
+						 UART_PARITY_SHIFT);
+					dev_dbg(dev, "Setting parity: MARK\n");
+				} else {
+					bits |= (UART_PARITY_SPACE <<
+						 UART_PARITY_SHIFT);
+					dev_dbg(dev, "Setting parity: SPACE\n");
+				}
+			} else {
+				if (cflag & PARODD) {
+					bits |= (UART_PARITY_ODD <<
+						 UART_PARITY_SHIFT);
+					dev_dbg(dev, "Setting parity: ODD\n");
+				} else {
+					bits |= (UART_PARITY_EVEN <<
+						 UART_PARITY_SHIFT);
+					dev_dbg(dev, "Setting parity: EVEN\n");
+				}
+			}
+		}
+	}
+
+	if ((cflag & CSTOPB) != (old_cflag & CSTOPB)) {
+		bits &= ~UART_STOP_MASK;
+		if (cflag & CSTOPB) {
+			bits |= (UART_STOP_2 << UART_STOP_SHIFT);
+			dev_dbg(dev, "Setting stop bits: 2\n");
+		} else {
+			bits |= (UART_STOP_1 << UART_STOP_SHIFT);
+			dev_dbg(dev, "Setting stop bits: 1\n");
+		}
+	}
+
+	ret = xr_set_reg(port, XR21V141X_UART_REG_BLOCK,
+			 port_priv->regs->format, (bits & 0xff));
+	if (ret)
+		return;
+
+	xr_set_flow_mode(tty, port, cflag);
+}
+
+static int xr_tiocmset_port(struct usb_serial_port *port,
+			    unsigned int set, unsigned int clear)
+{
+	struct xr_port_private *port_priv = usb_get_serial_port_data(port);
+	int ret = 0;
+	u8 gpio_set = 0;
+	u8 gpio_clr = 0;
+
+	/* Modem control pins are active low, so set & clr are swapped */
+	if (set & TIOCM_RTS)
+		gpio_clr |= UART_MODE_RTS;
+	if (set & TIOCM_DTR)
+		gpio_clr |= UART_MODE_DTR;
+	if (clear & TIOCM_RTS)
+		gpio_set |= UART_MODE_RTS;
+	if (clear & TIOCM_DTR)
+		gpio_set |= UART_MODE_DTR;
+
+	/* Writing '0' to gpio_{set/clr} bits has no effect, so no need to do */
+	if (gpio_clr)
+		ret = xr_set_reg(port, XR21V141X_UART_REG_BLOCK,
+				 port_priv->regs->gpio_clr, gpio_clr);
+
+	if (gpio_set)
+		ret = xr_set_reg(port, XR21V141X_UART_REG_BLOCK,
+				 port_priv->regs->gpio_set, gpio_set);
+
+	return ret;
+}
+
+static int xr_tiocmset(struct tty_struct *tty,
+		       unsigned int set, unsigned int clear)
+{
+	struct usb_serial_port *port = tty->driver_data;
+
+	return xr_tiocmset_port(port, set, clear);
+}
+
+static void xr_dtr_rts(struct usb_serial_port *port, int on)
+{
+	if (on)
+		xr_tiocmset_port(port, TIOCM_DTR | TIOCM_RTS, 0);
+	else
+		xr_tiocmset_port(port, 0, TIOCM_DTR | TIOCM_RTS);
+}
+
+static int xr_tiocmget(struct tty_struct *tty)
+{
+	struct usb_serial_port *port = tty->driver_data;
+	struct xr_port_private *port_priv = usb_get_serial_port_data(port);
+	int ret;
+	u8 status;
+
+	ret = xr_get_reg(port, XR21V141X_UART_REG_BLOCK,
+			 port_priv->regs->gpio_status, &status);
+	if (ret)
+		return ret;
+
+	/*
+	 * Modem control pins are active low, so reading '0' means it is active
+	 * and '1' means not active.
+	 */
+	ret = ((status & UART_MODE_DTR) ? 0 : TIOCM_DTR) |
+	      ((status & UART_MODE_RTS) ? 0 : TIOCM_RTS) |
+	      ((status & UART_MODE_CTS) ? 0 : TIOCM_CTS) |
+	      ((status & UART_MODE_DSR) ? 0 : TIOCM_DSR) |
+	      ((status & UART_MODE_RI) ? 0 : TIOCM_RI) |
+	      ((status & UART_MODE_CD) ? 0 : TIOCM_CD);
+
+	return ret;
+}
+
+static void xr_break_ctl(struct tty_struct *tty, int break_state)
+{
+	struct usb_serial_port *port = tty->driver_data;
+	struct xr_port_private *port_priv = usb_get_serial_port_data(port);
+	u8 state;
+
+	if (break_state == 0)
+		state = UART_BREAK_OFF;
+	else
+		state = UART_BREAK_ON;
+
+	dev_dbg(&port->dev, "Turning break %s\n",
+		state == UART_BREAK_OFF ? "off" : "on");
+	xr_set_reg(port, XR21V141X_UART_REG_BLOCK, port_priv->regs->tx_break,
+		   state);
+}
+
+static int xr_port_probe(struct usb_serial_port *port)
+{
+	struct xr_port_private *port_priv;
+
+	port_priv = kzalloc(sizeof(*port_priv), GFP_KERNEL);
+	if (!port_priv)
+		return -ENOMEM;
+
+	/* XR21V141X specific settings */
+	port_priv->regs = &xr21v141x_regs;
+
+	usb_set_serial_port_data(port, port_priv);
+
+	return 0;
+}
+
+static int xr_port_remove(struct usb_serial_port *port)
+{
+	struct xr_port_private *port_priv = usb_get_serial_port_data(port);
+
+	kfree(port_priv);
+
+	return 0;
+}
+
+static const struct usb_device_id id_table[] = {
+	{ USB_DEVICE(0x04e2, 0x1410) }, /* XR21V141X */
+	{ }
+};
+MODULE_DEVICE_TABLE(usb, id_table);
+
+static struct usb_serial_driver xr_device = {
+	.driver = {
+		.owner = THIS_MODULE,
+		.name =	"xr_serial",
+	},
+	.id_table		= id_table,
+	.num_ports		= 1,
+	.bulk_in_size		= 384,
+	.bulk_out_size		= 128,
+	.open			= xr_open,
+	.close			= xr_close,
+	.break_ctl		= xr_break_ctl,
+	.set_termios		= xr_set_termios,
+	.tiocmget		= xr_tiocmget,
+	.tiocmset		= xr_tiocmset,
+	.port_probe		= xr_port_probe,
+	.port_remove		= xr_port_remove,
+	.dtr_rts		= xr_dtr_rts
+};
+
+static struct usb_serial_driver * const serial_drivers[] = {
+	&xr_device, NULL
+};
+
+module_usb_serial_driver(serial_drivers, id_table);
+
+MODULE_AUTHOR("Manivannan Sadhasivam <mani@kernel.org>");
+MODULE_DESCRIPTION("MaxLinear/Exar USB to Serial driver");
+MODULE_LICENSE("GPL");
-- 
2.17.1