Add support for MaxLinear/Exar USB to serial converters

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index bb7df79cc129..2240fbc9ea7f 100644
@@ -10,6 +10,7 @@
  * Copyright (c) 2020 Manivannan Sadhasivam <[email protected]>
  */
 
+#include <linux/gpio/driver.h>
 #include <linux/kernel.h>
 #include <linux/module.h>
 #include <linux/slab.h>

@@ -17,6 +18,18 @@
 #include <linux/usb.h>
 #include <linux/usb/serial.h>
 
+#ifdef CONFIG_GPIOLIB
+enum gpio_pins {
+	GPIO_RI = 0,
+	GPIO_CD,
+	GPIO_DSR,
+	GPIO_DTR,
+	GPIO_CTS,
+	GPIO_RTS,
+	GPIO_MAX,
+};
+#endif
+
 static void xr_set_termios(struct tty_struct *tty,
 			   struct usb_serial_port *port,
 			   struct ktermios *old_termios);

@@ -39,6 +52,11 @@ struct xr_uart_regs {
 };
 
 struct xr_port_private {
+#ifdef CONFIG_GPIOLIB
+	struct gpio_chip gc;
+	bool gpio_registered;
+	enum gpio_pins pin_status[GPIO_MAX];
+#endif
 	const struct xr_uart_regs *regs;
 	bool port_open;
 };

@@ -390,6 +408,13 @@ static void xr_set_flow_mode(struct tty_struct *tty,
 	 */
 	gpio_mode &= ~UART_MODE_GPIO_MASK;
 	if (cflag & CRTSCTS) {
+#ifdef CONFIG_GPIOLIB
+		/* Check if the CTS/RTS pins are occupied */
+		if (port_priv->pin_status[GPIO_RTS] ||
+		    port_priv->pin_status[GPIO_CTS])
+			return;
+#endif
+
 		dev_dbg(&port->dev, "Enabling hardware flow ctrl\n");
 		flow = UART_FLOW_MODE_HW;
 		gpio_mode |= UART_MODE_RTS_CTS;

@@ -497,6 +522,17 @@ static int xr_tiocmset_port(struct usb_serial_port *port,
 	u8 gpio_set = 0;
 	u8 gpio_clr = 0;
 
+#ifdef CONFIG_GPIOLIB
+	/* Check if the RTS/DTR pins are occupied */
+	if (set & TIOCM_RTS || clear & TIOCM_RTS)
+		if (port_priv->pin_status[GPIO_RTS])
+			return -EBUSY;
+
+	if (set & TIOCM_DTR || clear & TIOCM_DTR)
+		if (port_priv->pin_status[GPIO_DTR])
+			return -EBUSY;
+#endif
+
 	/* Modem control pins are active low, so set & clr are swapped */
 	if (set & TIOCM_RTS)
 		gpio_clr |= UART_MODE_RTS;

@@ -589,9 +625,175 @@ static void xr_break_ctl(struct tty_struct *tty, int break_state)
 		   state);
 }
 
+#ifdef CONFIG_GPIOLIB
+
+static int xr_gpio_request(struct gpio_chip *gc, unsigned int offset)
+{
+	struct usb_serial_port *port = gpiochip_get_data(gc);
+	struct xr_port_private *port_priv = usb_get_serial_port_data(port);
+
+	/*
+	 * Do not proceed if the port is open. This is done to avoid changing
+	 * the GPIO configuration used by the serial driver.
+	 */
+	if (port_priv->port_open)
+		return -EBUSY;
+
+	/* Mark the GPIO pin as busy */
+	port_priv->pin_status[offset] = true;
+
+	return 0;
+}
+
+static void xr_gpio_free(struct gpio_chip *gc, unsigned int offset)
+{
+	struct usb_serial_port *port = gpiochip_get_data(gc);
+	struct xr_port_private *port_priv = usb_get_serial_port_data(port);
+
+	/* Mark the GPIO pin as free */
+	port_priv->pin_status[offset] = false;
+}
+
+static int xr_gpio_get(struct gpio_chip *gc, unsigned int gpio)
+{
+	struct usb_serial_port *port = gpiochip_get_data(gc);
+	struct xr_port_private *port_priv = usb_get_serial_port_data(port);
+	int ret;
+	u8 gpio_status;
+
+	ret = xr_get_reg(port, XR21V141X_UART_REG_BLOCK,
+			 port_priv->regs->gpio_status, &gpio_status);
+	if (ret)
+		return ret;
+
+	return !!(gpio_status & BIT(gpio));
+}
+
+static void xr_gpio_set(struct gpio_chip *gc, unsigned int gpio, int val)
+{
+	struct usb_serial_port *port = gpiochip_get_data(gc);
+	struct xr_port_private *port_priv = usb_get_serial_port_data(port);
+
+	if (val)
+		xr_set_reg(port, XR21V141X_UART_REG_BLOCK,
+			   port_priv->regs->gpio_set, BIT(gpio));
+	else
+		xr_set_reg(port, XR21V141X_UART_REG_BLOCK,
+			   port_priv->regs->gpio_clr, BIT(gpio));
+}
+
+static int xr_gpio_direction_get(struct gpio_chip *gc, unsigned int gpio)
+{
+	struct usb_serial_port *port = gpiochip_get_data(gc);
+	struct xr_port_private *port_priv = usb_get_serial_port_data(port);
+	int ret;
+	u8 gpio_dir;
+
+	ret = xr_get_reg(port, XR21V141X_UART_REG_BLOCK,
+			 port_priv->regs->gpio_dir, &gpio_dir);
+	if (ret)
+		return ret;
+
+	/* Logic 0 = input and Logic 1 = output */
+	return !(gpio_dir & BIT(gpio));
+}
+
+static int xr_gpio_direction_input(struct gpio_chip *gc, unsigned int gpio)
+{
+	struct usb_serial_port *port = gpiochip_get_data(gc);
+	struct xr_port_private *port_priv = usb_get_serial_port_data(port);
+	int ret;
+	u8 gpio_dir;
+
+	ret = xr_get_reg(port, XR21V141X_UART_REG_BLOCK,
+			 port_priv->regs->gpio_dir, &gpio_dir);
+	if (ret)
+		return ret;
+
+	gpio_dir &= ~BIT(gpio);
+
+	return xr_set_reg(port, XR21V141X_UART_REG_BLOCK,
+			  port_priv->regs->gpio_dir, gpio_dir);
+}
+
+static int xr_gpio_direction_output(struct gpio_chip *gc, unsigned int gpio,
+				    int val)
+{
+	struct usb_serial_port *port = gpiochip_get_data(gc);
+	struct xr_port_private *port_priv = usb_get_serial_port_data(port);
+	int ret;
+	u8 gpio_dir;
+
+	xr_gpio_set(gc, gpio, val);
+
+	ret = xr_get_reg(port, XR21V141X_UART_REG_BLOCK,
+			 port_priv->regs->gpio_dir, &gpio_dir);
+	if (ret)
+		return ret;
+
+	gpio_dir |= BIT(gpio);
+
+	ret = xr_set_reg(port, XR21V141X_UART_REG_BLOCK,
+			 port_priv->regs->gpio_dir, gpio_dir);
+	if (ret)
+		return ret;
+
+	return 0;
+}
+
+static int xr_gpio_init(struct usb_serial_port *port)
+{
+	struct xr_port_private *port_priv = usb_get_serial_port_data(port);
+	int ret = 0;
+
+	port_priv->gc.ngpio = 6;
+	port_priv->gc.label = "xr_gpios";
+	port_priv->gc.request = xr_gpio_request;
+	port_priv->gc.free = xr_gpio_free;
+	port_priv->gc.get_direction = xr_gpio_direction_get;
+	port_priv->gc.direction_input = xr_gpio_direction_input;
+	port_priv->gc.direction_output = xr_gpio_direction_output;
+	port_priv->gc.get = xr_gpio_get;
+	port_priv->gc.set = xr_gpio_set;
+	port_priv->gc.owner = THIS_MODULE;
+	port_priv->gc.parent = &port->dev;
+	port_priv->gc.base = -1;
+	port_priv->gc.can_sleep = true;
+
+	ret = gpiochip_add_data(&port_priv->gc, port);
+	if (!ret)
+		port_priv->gpio_registered = true;
+
+	return ret;
+}
+
+static void xr_gpio_remove(struct usb_serial_port *port)
+{
+	struct xr_port_private *port_priv = usb_get_serial_port_data(port);
+
+	if (port_priv->gpio_registered) {
+		gpiochip_remove(&port_priv->gc);
+		port_priv->gpio_registered = false;
+	}
+}
+
+#else
+
+static int xr_gpio_init(struct usb_serial_port *port)
+{
+	return 0;
+}
+
+static void xr_gpio_remove(struct usb_serial_port *port)
+{
+}
+
+#endif
+
 static int xr_port_probe(struct usb_serial_port *port)
 {
 	struct xr_port_private *port_priv;
+	int ret;
 
 	port_priv = kzalloc(sizeof(*port_priv), GFP_KERNEL);
 	if (!port_priv)

@@ -602,13 +804,18 @@ static int xr_port_probe(struct usb_serial_port *port)
 
 	usb_set_serial_port_data(port, port_priv);
 
-	return 0;
+	ret = xr_gpio_init(port);
+	if (ret)
+		kfree(port_priv);
+
+	return ret;
 }
 
 static int xr_port_remove(struct usb_serial_port *port)
 {
 	struct xr_port_private *port_priv = usb_get_serial_port_data(port);
 
+	xr_gpio_remove(port);
 	kfree(port_priv);
 
 	return 0;

index 84d6f7df09a4..30e20d06d044 100644
@@ -1864,6 +1864,12 @@ static const struct usb_device_id acm_ids[] = {
 	},
 #endif
 
+#if IS_ENABLED(CONFIG_USB_SERIAL_XR)
+	{ USB_DEVICE(0x04e2, 0x1410),   /* Ignore XR21V141X USB to Serial converter */
+	.driver_info = IGNORE_DEVICE,
+	},
+#endif
+
 	/*Samsung phone in firmware update mode */
 	{ USB_DEVICE(0x04e8, 0x685d),
 	.driver_info = IGNORE_DEVICE,