[PATCH 01/13] HID: ft260: add serial driver

[Michael Zaidman]

From: Christina Quast <contact@xxxxxxxxxxxxxxxxxx>

Add a TTY serial interface (/dev/ttyFTx) for FT260 USB HID devices,
providing baud rate configuration, data transfer, and termios settings
without requiring userspace HID report formatting.

The FT260 exposes I2C and UART through separate HID interfaces. Only
I2C was supported previously; UART required FTDI hidraw example code.

This is a port of the v4 patch, adapted to the I2C hardening that has
since been merged upstream: input-report length validation, the
read_buf/raw_event race fix with read_lock, and SMBus block-read
START/STOP handling. HID_FT260 now depends on TTY because the UART code
is part of this driver.

Routing UART reports through ft260_raw_event() also made v4 fall through
the report dispatch after an I2C input report had already been consumed,
so every I2C input report was additionally reported as unhandled. This
regression is fixed here.

Ported from:
https://lore.kernel.org/all/20231218093153.192268-1-contact@xxxxxxxxxxxxxxxxxx/

The follow-up v5 series stalled without being applied:
https://lore.kernel.org/linux-input/20240216-ft260_review5-v5-1-36db44673ac7@xxxxxxxxxxxxxxxxxx/

Signed-off-by: Christina Quast <contact@xxxxxxxxxxxxxxxxxx>
Co-developed-by: Daniel Beer <daniel.beer@xxxxxxxxxxxxxxxxx>
Signed-off-by: Daniel Beer <daniel.beer@xxxxxxxxxxxxxxxxx>
Co-developed-by: Michael Zaidman <michael.zaidman@xxxxxxxxx>
Signed-off-by: Michael Zaidman <michael.zaidman@xxxxxxxxx>
---
 drivers/hid/Kconfig     |  10 +-
 drivers/hid/hid-ft260.c | 842 +++++++++++++++++++++++++++++++++++++---
 2 files changed, 790 insertions(+), 62 deletions(-)

diff --git a/drivers/hid/Kconfig b/drivers/hid/Kconfig
index aa7fa11a0197..e898adb331ba 100644
--- a/drivers/hid/Kconfig
+++ b/drivers/hid/Kconfig
@@ -386,12 +386,12 @@ config HID_EZKEY
 	Support for Ezkey BTC 8193 keyboard.
 
 config HID_FT260
-	tristate "FTDI FT260 USB HID to I2C host support"
-	depends on USB_HID && HIDRAW && I2C
+	tristate "FTDI FT260 USB HID to I2C/UART host support"
+	depends on USB_HID && HIDRAW && I2C && TTY
 	help
-	  Provides I2C host adapter functionality over USB-HID through FT260
-	  device. The customizable USB descriptor fields are exposed as sysfs
-	  attributes.
+	  Provides I2C host adapter and UART/TTY functionality over USB-HID
+	  through the FT260 device. The customizable USB descriptor fields
+	  are exposed as sysfs attributes.
 
 	  To compile this driver as a module, choose M here: the module
 	  will be called hid-ft260.
diff --git a/drivers/hid/hid-ft260.c b/drivers/hid/hid-ft260.c
index 64c9c940db46..3faedfc5c413 100644
--- a/drivers/hid/hid-ft260.c
+++ b/drivers/hid/hid-ft260.c
@@ -13,6 +13,16 @@
 #include <linux/i2c.h>
 #include <linux/module.h>
 #include <linux/usb.h>
+#include <linux/serial.h>
+#include <linux/serial_core.h>
+#include <linux/kfifo.h>
+#include <linux/tty_flip.h>
+#include <linux/minmax.h>
+#include <linux/unaligned.h>
+
+#define UART_COUNT_MAX		4	/* Number of UARTs this driver can handle */
+#define FIFO_SIZE	256
+#define TTY_WAKEUP_WATERMARK	(FIFO_SIZE / 2)
 
 #ifdef DEBUG
 static int ft260_debug = 1;
@@ -30,6 +40,7 @@ MODULE_PARM_DESC(debug, "Toggle FT260 debugging messages");
 
 #define FT260_REPORT_MAX_LENGTH (64)
 #define FT260_I2C_DATA_REPORT_ID(len) (FT260_I2C_REPORT_MIN + (len - 1) / 4)
+#define FT260_UART_DATA_REPORT_ID(len) (FT260_UART_REPORT_MIN + (len - 1) / 4)
 
 #define FT260_WAKEUP_NEEDED_AFTER_MS (4800) /* 5s minus 200ms margin */
 
@@ -43,7 +54,7 @@ MODULE_PARM_DESC(debug, "Toggle FT260 debugging messages");
  * or optoe limit the i2c reads to 128 bytes. To not block other drivers out
  * of I2C for potentially troublesome amounts of time, we select the maximum
  * read payload length to be 180 bytes.
-*/
+ */
 #define FT260_RD_DATA_MAX (180)
 #define FT260_WR_DATA_MAX (60)
 
@@ -81,7 +92,8 @@ enum {
 	FT260_UART_INTERRUPT_STATUS	= 0xB1,
 	FT260_UART_STATUS		= 0xE0,
 	FT260_UART_RI_DCD_STATUS	= 0xE1,
-	FT260_UART_REPORT		= 0xF0,
+	FT260_UART_REPORT_MIN		= 0xF0,
+	FT260_UART_REPORT_MAX		= 0xFE,
 };
 
 /* Feature Out */
@@ -132,6 +144,13 @@ enum {
 	FT260_FLAG_START_STOP_REPEATED	= 0x07,
 };
 
+/* Return values for ft260_get_interface_type func */
+enum {
+	FT260_IFACE_NONE,
+	FT260_IFACE_I2C,
+	FT260_IFACE_UART
+};
+
 #define FT260_SET_REQUEST_VALUE(report_id) ((FT260_FEATURE << 8) | report_id)
 
 /* Feature In reports */
@@ -220,12 +239,59 @@ struct ft260_i2c_read_request_report {
 	__le16 length;		/* data payload length */
 } __packed;
 
-struct ft260_i2c_input_report {
-	u8 report;		/* FT260_I2C_REPORT */
+struct ft260_input_report {
+	u8 report;		/* FT260_I2C_REPORT or FT260_UART_REPORT */
 	u8 length;		/* data payload length */
 	u8 data[2];		/* data payload */
 } __packed;
 
+/* UART reports */
+struct ft260_uart_write_request_report {
+	u8 report;		/* FT260_UART_REPORT */
+	u8 length;		/* data payload length */
+	u8 data[] __counted_by(length);	/* variable data payload */
+} __packed;
+
+struct ft260_configure_uart_request {
+	u8 report;		/* FT260_SYSTEM_SETTINGS */
+	u8 request;		/* FT260_SET_UART_CONFIG */
+	u8 flow_ctrl;		/* 0: OFF, 1: RTS_CTS, 2: DTR_DSR */
+				/* 3: XON_XOFF, 4: No flow ctrl */
+	/* The baudrate field is unaligned: */
+	__le32 baudrate;	/* little endian, 9600 = 0x2580, 19200 = 0x4B00 */
+	u8 data_bit;		/* 7 or 8 */
+	u8 parity;		/* 0: no parity, 1: odd, 2: even, 3: high, 4: low */
+	u8 stop_bit;		/* 0: one stop bit, 2: 2 stop bits */
+	u8 breaking;		/* 0: no break */
+} __packed;
+
+/* UART interface configuration */
+enum {
+	FT260_CFG_FLOW_CTRL_OFF		= 0x00,
+	FT260_CFG_FLOW_CTRL_RTS_CTS	= 0x01,
+	FT260_CFG_FLOW_CTRL_DTR_DSR	= 0x02,
+	FT260_CFG_FLOW_CTRL_XON_XOFF	= 0x03,
+	FT260_CFG_FLOW_CTRL_NONE	= 0x04,
+
+	FT260_CFG_DATA_BITS_7		= 0x07,
+	FT260_CFG_DATA_BITS_8		= 0x08,
+
+	FT260_CFG_PAR_NO		= 0x00,
+	FT260_CFG_PAR_ODD		= 0x01,
+	FT260_CFG_PAR_EVEN		= 0x02,
+	FT260_CFG_PAR_HIGH		= 0x03,
+	FT260_CFG_PAR_LOW		= 0x04,
+
+	FT260_CFG_STOP_ONE_BIT		= 0x00,
+	FT260_CFG_STOP_TWO_BIT		= 0x02,
+
+	FT260_CFG_BREAKING_NO		= 0x00,
+	FT260_CFG_BEAKING_YES		= 0x01,
+
+	FT260_CFG_BAUD_MIN		= 1200,
+	FT260_CFG_BAUD_MAX		= 12000000,
+};
+
 static const struct hid_device_id ft260_devices[] = {
 	{ HID_USB_DEVICE(USB_VENDOR_ID_FUTURE_TECHNOLOGY,
 			 USB_DEVICE_ID_FT260) },
@@ -236,6 +302,23 @@ MODULE_DEVICE_TABLE(hid, ft260_devices);
 struct ft260_device {
 	struct i2c_adapter adap;
 	struct hid_device *hdev;
+
+	bool ft260_is_serial;
+	struct list_head device_list;
+
+	/* tty_port lifetime is equal to device lifetime */
+	struct tty_port port;
+	unsigned int index;
+	struct kfifo xmit_fifo;
+	/* write_lock: lock to serialize access to xmit fifo */
+	spinlock_t write_lock;
+	struct uart_icount icount;
+
+	struct timer_list wakeup_timer;
+	struct work_struct wakeup_work;
+	bool reschedule_work;
+
+
 	struct completion wait;
 	struct mutex lock;
 	u8 write_buf[FT260_REPORT_MAX_LENGTH];
@@ -379,7 +462,7 @@ static int ft260_hid_output_report_check_status(struct ft260_device *dev,
 
 	ret = ft260_hid_output_report(hdev, data, len);
 	if (ret < 0) {
-		hid_err(hdev, "%s: failed to start transfer, ret %d\n",
+		hid_dbg(hdev, "%s: failed to start transfer, ret %d\n",
 			__func__, ret);
 		ft260_i2c_reset(hdev);
 		return ret;
@@ -609,7 +692,7 @@ static int ft260_i2c_write_read(struct ft260_device *dev, struct i2c_msg *msgs)
 		else
 			read_off = *msgs[0].buf;
 
-		pr_info("%s: off %#x rlen %d wlen %d\n", __func__,
+		ft260_dbg("%s: off %#x rlen %d wlen %d\n", __func__,
 			read_off, rd_len, wr_len);
 	}
 
@@ -826,7 +909,7 @@ static int ft260_get_system_config(struct hid_device *hdev,
 	return 0;
 }
 
-static int ft260_is_interface_enabled(struct hid_device *hdev)
+static int ft260_get_interface_type(struct hid_device *hdev, struct ft260_device *dev)
 {
 	struct ft260_get_system_status_report cfg;
 	struct usb_interface *usbif = to_usb_interface(hdev->dev.parent);
@@ -843,21 +926,27 @@ static int ft260_is_interface_enabled(struct hid_device *hdev)
 	ft260_dbg("i2c_enable: 0x%02x\n", cfg.i2c_enable);
 	ft260_dbg("uart_mode:  0x%02x\n", cfg.uart_mode);
 
+	dev->ft260_is_serial = false;
+
 	switch (cfg.chip_mode) {
 	case FT260_MODE_ALL:
 	case FT260_MODE_BOTH:
-		if (interface == 1)
-			hid_info(hdev, "uart interface is not supported\n");
-		else
-			ret = 1;
+		if (interface == 1) {
+			ret = FT260_IFACE_UART;
+			dev->ft260_is_serial = true;
+		} else {
+			ret = FT260_IFACE_I2C;
+		}
 		break;
 	case FT260_MODE_UART:
-		hid_info(hdev, "uart interface is not supported\n");
+		ret = FT260_IFACE_UART;
+		dev->ft260_is_serial = true;
 		break;
 	case FT260_MODE_I2C:
-		ret = 1;
+		ret = FT260_IFACE_I2C;
 		break;
 	}
+
 	return ret;
 }
 
@@ -1001,6 +1090,583 @@ static const struct attribute_group ft260_attr_group = {
 	}
 };
 
+/***
+ * START Serial dev part
+ */
+static DEFINE_MUTEX(ft260_uart_list_lock);
+static LIST_HEAD(ft260_uart_device_list);
+
+static struct ft260_device *ft260_dev_by_index(int index)
+{
+	struct ft260_device *port;
+
+	list_for_each_entry(port, &ft260_uart_device_list, device_list) {
+		if (index == port->index)
+			return port;
+	}
+	return NULL;
+}
+
+static int ft260_uart_add_port(struct ft260_device *port)
+{
+	int index = 0, ret = 0;
+	struct ft260_device *dev;
+
+	spin_lock_init(&port->write_lock);
+	if (kfifo_alloc(&port->xmit_fifo, FIFO_SIZE, GFP_KERNEL))
+		return -ENOMEM;
+
+	mutex_lock(&ft260_uart_list_lock);
+	list_for_each_entry(dev, &ft260_uart_device_list, device_list) {
+		if (dev->index != index)
+			break;
+		index++;
+	}
+
+	port->index = index;
+	list_add(&port->device_list, &ft260_uart_device_list);
+	mutex_unlock(&ft260_uart_list_lock);
+
+	return ret;
+}
+
+static void ft260_uart_port_put(struct ft260_device *port)
+{
+	tty_port_put(&port->port);
+}
+
+static void ft260_uart_port_remove(struct ft260_device *port)
+{
+	timer_delete_sync(&port->wakeup_timer);
+
+	mutex_lock(&ft260_uart_list_lock);
+	list_del(&port->device_list);
+	mutex_unlock(&ft260_uart_list_lock);
+
+	spin_lock(&port->write_lock);
+	kfifo_free(&port->xmit_fifo);
+	spin_unlock(&port->write_lock);
+
+	mutex_lock(&port->port.mutex);
+	port->reschedule_work = false;
+	tty_port_tty_hangup(&port->port, false);
+	mutex_unlock(&port->port.mutex);
+
+	ft260_uart_port_put(port);
+}
+
+static struct ft260_device *ft260_uart_port_get(unsigned int index)
+{
+	struct ft260_device *port;
+
+	if (index >= UART_COUNT_MAX)
+		return NULL;
+
+	mutex_lock(&ft260_uart_list_lock);
+	port = ft260_dev_by_index(index);
+	if (port)
+		tty_port_get(&port->port);
+	mutex_unlock(&ft260_uart_list_lock);
+
+	return port;
+}
+
+static int ft260_uart_open(struct tty_struct *tty, struct file *filp)
+{
+	int ret;
+	struct ft260_device *port = tty->driver_data;
+
+	ret = tty_port_open(&port->port, tty, filp);
+
+	return ret;
+}
+
+static void ft260_uart_close(struct tty_struct *tty, struct file *filp)
+{
+	struct ft260_device *port = tty->driver_data;
+
+	tty_port_close(&port->port, tty, filp);
+}
+
+static void ft260_uart_hangup(struct tty_struct *tty)
+{
+	struct ft260_device *port = tty->driver_data;
+
+	tty_port_hangup(&port->port);
+}
+
+static int ft260_uart_transmit_chars(struct ft260_device *port)
+{
+	struct hid_device *hdev = port->hdev;
+	struct kfifo *xmit = &port->xmit_fifo;
+	struct tty_struct *tty;
+	struct ft260_uart_write_request_report *rep;
+	int len, data_len, ret = 0;
+
+	tty = tty_port_tty_get(&port->port);
+
+	data_len = kfifo_len(xmit);
+	if (!tty || !data_len) {
+		ret = -EINVAL;
+		goto tty_out;
+	}
+
+	rep = (struct ft260_uart_write_request_report *)port->write_buf;
+
+	do {
+		len = min(data_len, FT260_WR_DATA_MAX);
+
+		rep->report = FT260_UART_DATA_REPORT_ID(len);
+		rep->length = len;
+
+		len = kfifo_out_locked(xmit, rep->data, len, &port->write_lock);
+
+		ret = ft260_hid_output_report(hdev, (u8 *)rep, len + sizeof(*rep));
+		if (ret < 0) {
+			hid_err(hdev, "Failed to start transfer, ret %d\n", ret);
+			goto tty_out;
+		}
+
+		data_len -= len;
+		port->icount.tx += len;
+	} while (data_len > 0);
+
+	len = kfifo_len(xmit);
+	if ((FIFO_SIZE - len) > TTY_WAKEUP_WATERMARK)
+		tty_wakeup(tty);
+
+	ret = 0;
+
+tty_out:
+	tty_kref_put(tty);
+	return ret;
+}
+
+static int ft260_uart_receive_chars(struct ft260_device *port,
+				    u8 *data, u8 length)
+{
+	struct hid_device *hdev = port->hdev;
+	int ret = 0;
+
+	if (length > FT260_RD_DATA_MAX) {
+		hid_err(hdev, "Received too much data (%d)\n", length);
+		return -EBADR;
+	}
+
+	ret = tty_insert_flip_string(&port->port, data, length);
+	if (ret != length)
+		hid_err(hdev, "%d char not inserted to flip buffer\n", length - ret);
+	port->icount.rx += ret;
+
+	if (ret)
+		tty_flip_buffer_push(&port->port);
+
+	return ret;
+}
+
+static ssize_t ft260_uart_write(struct tty_struct *tty, const u8 *buf,
+				 size_t count)
+{
+	struct ft260_device *port = tty->driver_data;
+	struct hid_device *hdev = port->hdev;
+	int len, ret;
+
+	len = kfifo_in_locked(&port->xmit_fifo, buf, count, &port->write_lock);
+	ft260_dbg("count: %zu, len: %d", count, len);
+
+	ret = ft260_uart_transmit_chars(port);
+	if (ret < 0) {
+		hid_dbg(hdev, "Failed to transmit chars: %d\n", ret);
+		return 0;
+	}
+
+	ret = kfifo_len(&port->xmit_fifo);
+	if (ret > 0) {
+		hid_dbg(hdev, "Failed to  all kfifo data bytes\n");
+		ft260_dbg("return: %d", len - ret);
+		return len - ret;
+	}
+
+	return len;
+}
+
+static unsigned int ft260_uart_write_room(struct tty_struct *tty)
+{
+	struct ft260_device *port = tty->driver_data;
+
+	return FIFO_SIZE - kfifo_len(&port->xmit_fifo);
+}
+
+static unsigned int ft260_uart_chars_in_buffer(struct tty_struct *tty)
+{
+	struct ft260_device *port = tty->driver_data;
+
+	return kfifo_len(&port->xmit_fifo);
+}
+
+static int ft260_uart_change_speed(struct ft260_device *port,
+				   struct ktermios *termios,
+				    struct ktermios *old)
+{
+	struct hid_device *hdev = port->hdev;
+	unsigned int baud;
+	struct ft260_configure_uart_request req;
+	int ret;
+
+	memset(&req, 0, sizeof(req));
+
+	req.report = FT260_SYSTEM_SETTINGS;
+	req.request = FT260_SET_UART_CONFIG;
+
+	switch (termios->c_cflag & CSIZE) {
+	case CS7:
+		req.data_bit = FT260_CFG_DATA_BITS_7;
+		break;
+	case CS5:
+	case CS6:
+		hid_err(hdev, "Invalid data bit size, setting to default (8 bit)\n");
+		req.data_bit = FT260_CFG_DATA_BITS_8;
+		termios->c_cflag &= ~CSIZE;
+		termios->c_cflag |= CS8;
+		break;
+	default:
+	case CS8:
+		req.data_bit = FT260_CFG_DATA_BITS_8;
+		break;
+	}
+
+	req.stop_bit = (termios->c_cflag & CSTOPB) ?
+		FT260_CFG_STOP_TWO_BIT : FT260_CFG_STOP_ONE_BIT;
+
+	if (termios->c_cflag & PARENB) {
+		req.parity = (termios->c_cflag & PARODD) ?
+			FT260_CFG_PAR_ODD : FT260_CFG_PAR_EVEN;
+	} else {
+		req.parity = FT260_CFG_PAR_NO;
+	}
+
+	baud = tty_termios_baud_rate(termios);
+	if (baud == 0 || baud < FT260_CFG_BAUD_MIN || baud > FT260_CFG_BAUD_MAX) {
+		struct tty_struct *tty = tty_port_tty_get(&port->port);
+
+		hid_err(hdev, "Invalid baud rate %d\n", baud);
+		baud = 9600;
+		tty_encode_baud_rate(tty, baud, baud);
+		tty_kref_put(tty);
+	}
+	put_unaligned_le32(cpu_to_le32(baud), &req.baudrate);
+
+	if (termios->c_cflag & CRTSCTS)
+		req.flow_ctrl = FT260_CFG_FLOW_CTRL_RTS_CTS;
+	else
+		req.flow_ctrl = FT260_CFG_FLOW_CTRL_OFF;
+
+	ft260_dbg("Configured termios: flow control: %d, baudrate: %d, ",
+		  req.flow_ctrl, baud);
+	ft260_dbg("data_bit: %d, parity: %d, stop_bit: %d, breaking: %d\n",
+		  req.data_bit, req.parity,
+		  req.stop_bit, req.breaking);
+
+	req.flow_ctrl = FT260_CFG_FLOW_CTRL_NONE;
+	req.breaking = FT260_CFG_BREAKING_NO;
+
+	ret = ft260_hid_feature_report_set(hdev, (u8 *)&req, sizeof(req));
+	if (ret < 0)
+		hid_err(hdev, "ft260_hid_feature_report_set failed: %d\n", ret);
+
+	return ret;
+}
+
+static int ft260_uart_get_icount(struct tty_struct *tty,
+		struct serial_icounter_struct *icount)
+{
+	struct ft260_device *port = tty->driver_data;
+
+	memcpy(icount, &port->icount, sizeof(struct uart_icount));
+
+	return 0;
+}
+
+static void ft260_uart_set_termios(struct tty_struct *tty,
+		const struct ktermios *old_termios)
+{
+	struct ft260_device *port = tty->driver_data;
+
+	ft260_uart_change_speed(port, &tty->termios, NULL);
+}
+
+static int ft260_uart_install(struct tty_driver *driver, struct tty_struct *tty)
+{
+	int idx = tty->index;
+	struct ft260_device *port = ft260_uart_port_get(idx);
+	int ret = tty_standard_install(driver, tty);
+
+	if (ret == 0)
+		/* This is the ref ft260_uart_port get provided */
+		tty->driver_data = port;
+	else
+		ft260_uart_port_put(port);
+
+	return ret;
+}
+
+static void ft260_uart_cleanup(struct tty_struct *tty)
+{
+	struct ft260_device *port = tty->driver_data;
+
+	tty->driver_data = NULL;	/* Bug trap */
+	ft260_uart_port_put(port);
+}
+
+static int ft260_uart_proc_show(struct seq_file *m, void *v)
+{
+	int i;
+
+	seq_printf(m, "ft260 info:1.0 driver%s%s revision:%s\n",
+			"", "", "");
+	for (i = 0; i < UART_COUNT_MAX; i++) {
+		struct ft260_device *port = ft260_uart_port_get(i);
+
+		if (port) {
+			seq_printf(m, "%d: uart:FT260", i);
+			if (capable(CAP_SYS_ADMIN)) {
+				seq_printf(m, " tx:%d rx:%d",
+						port->icount.tx, port->icount.rx);
+				if (port->icount.frame)
+					seq_printf(m, " fe:%d",
+							port->icount.frame);
+				if (port->icount.parity)
+					seq_printf(m, " pe:%d",
+							port->icount.parity);
+				if (port->icount.brk)
+					seq_printf(m, " brk:%d",
+							port->icount.brk);
+				if (port->icount.overrun)
+					seq_printf(m, " oe:%d",
+							port->icount.overrun);
+				if (port->icount.cts)
+					seq_printf(m, " cts:%d",
+							port->icount.cts);
+				if (port->icount.dsr)
+					seq_printf(m, " dsr:%d",
+							port->icount.dsr);
+				if (port->icount.rng)
+					seq_printf(m, " rng:%d",
+							port->icount.rng);
+				if (port->icount.dcd)
+					seq_printf(m, " dcd:%d",
+							port->icount.dcd);
+			}
+			ft260_uart_port_put(port);
+			seq_putc(m, '\n');
+		}
+	}
+	return 0;
+}
+
+static const struct tty_operations ft260_uart_ops = {
+	.open			= ft260_uart_open,
+	.close			= ft260_uart_close,
+	.write			= ft260_uart_write,
+	.write_room		= ft260_uart_write_room,
+	.chars_in_buffer	= ft260_uart_chars_in_buffer,
+	.set_termios		= ft260_uart_set_termios,
+	.hangup			= ft260_uart_hangup,
+	.install		= ft260_uart_install,
+	.cleanup		= ft260_uart_cleanup,
+	.proc_show		= ft260_uart_proc_show,
+	.get_icount		= ft260_uart_get_icount,
+};
+
+/* The FT260 has a "power saving mode" that causes the device to switch
+ * to a 30 kHz oscillator if there's no activity for 5 seconds.
+ * Unfortunately this mode can only be disabled by reprogramming
+ * internal fuses, which requires an additional programming voltage.
+ *
+ * One effect of this mode is to cause data loss on a fast UART that
+ * transmits after being idle for longer than 5 seconds. We work around
+ * this by sending a dummy report at least once per 4 seconds if the
+ * UART is in use.
+ */
+static void ft260_uart_start_wakeup(struct timer_list *t)
+{
+	struct ft260_device *dev =
+		container_of(t, struct ft260_device, wakeup_timer);
+
+	if (dev->reschedule_work) {
+		schedule_work(&dev->wakeup_work);
+		mod_timer(&dev->wakeup_timer, jiffies +
+			msecs_to_jiffies(FT260_WAKEUP_NEEDED_AFTER_MS));
+	}
+}
+
+static void ft260_uart_do_wakeup(struct work_struct *work)
+{
+	struct ft260_device *dev =
+		container_of(work, struct ft260_device, wakeup_work);
+	struct ft260_get_chip_version_report version;
+	int ret;
+
+	if (dev->reschedule_work) {
+		ret = ft260_hid_feature_report_get(dev->hdev, FT260_CHIP_VERSION,
+					  (u8 *)&version, sizeof(version));
+		if (ret < 0)
+			hid_err(dev->hdev,
+				"%s: failed to start transfer, ret %d\n",
+				__func__, ret);
+	}
+}
+
+static void ft260_uart_shutdown(struct tty_port *tport)
+{
+	struct ft260_device *port =
+		container_of(tport, struct ft260_device, port);
+
+	port->reschedule_work = false;
+}
+
+static int ft260_uart_activate(struct tty_port *tport, struct tty_struct *tty)
+{
+	struct ft260_device *port =
+		container_of(tport, struct ft260_device, port);
+
+	/*
+	 * Set the TTY IO error marker - we will only clear this
+	 * once we have successfully opened the port.
+	 */
+	set_bit(TTY_IO_ERROR, &tty->flags);
+
+	spin_lock(&port->write_lock);
+	kfifo_reset(&port->xmit_fifo);
+	spin_unlock(&port->write_lock);
+
+	ft260_uart_change_speed(port, &tty->termios, NULL);
+	clear_bit(TTY_IO_ERROR, &tty->flags);
+
+	if (port->reschedule_work) {
+		mod_timer(&port->wakeup_timer, jiffies +
+			  msecs_to_jiffies(FT260_WAKEUP_NEEDED_AFTER_MS));
+	}
+
+	return 0;
+}
+
+static void ft260_uart_port_destroy(struct tty_port *tport)
+{
+	struct ft260_device *port =
+		container_of(tport, struct ft260_device, port);
+
+	kfree(port);
+}
+
+static const struct tty_port_operations ft260_uart_port_ops = {
+	.shutdown = ft260_uart_shutdown,
+	.activate = ft260_uart_activate,
+	.destruct = ft260_uart_port_destroy,
+};
+
+static struct tty_driver *ft260_tty_driver;
+
+static int ft260_i2c_probe(struct hid_device *hdev, struct ft260_device *dev)
+{
+	int ret;
+
+	hid_info(hdev, "USB HID v%x.%02x Device [%s] on %s\n",
+		hdev->version >> 8, hdev->version & 0xff, hdev->name,
+		hdev->phys);
+
+	hid_set_drvdata(hdev, dev);
+	dev->hdev = hdev;
+	dev->adap.owner = THIS_MODULE;
+	dev->adap.class = I2C_CLASS_HWMON;
+	dev->adap.algo = &ft260_i2c_algo;
+	dev->adap.quirks = &ft260_i2c_quirks;
+	dev->adap.dev.parent = &hdev->dev;
+	snprintf(dev->adap.name, sizeof(dev->adap.name),
+		 "FT260 usb-i2c bridge");
+
+	ret = ft260_xfer_status(dev, FT260_I2C_STATUS_BUS_BUSY);
+	if (ret)
+		ft260_i2c_reset(hdev);
+
+	i2c_set_adapdata(&dev->adap, dev);
+	ret = i2c_add_adapter(&dev->adap);
+	if (ret) {
+		hid_err(hdev, "failed to add i2c adapter\n");
+		return ret;
+	}
+
+	ret = sysfs_create_group(&hdev->dev.kobj, &ft260_attr_group);
+	if (ret < 0) {
+		hid_err(hdev, "failed to create sysfs attrs\n");
+		goto err_i2c_free;
+	}
+	return 0;
+
+err_i2c_free:
+	i2c_del_adapter(&dev->adap);
+	return ret;
+}
+
+static int ft260_uart_probe(struct hid_device *hdev, struct ft260_device *dev)
+{
+	struct ft260_configure_uart_request req;
+	int ret;
+	struct device *devt;
+
+	INIT_WORK(&dev->wakeup_work, ft260_uart_do_wakeup);
+	// FIXME: Do I need that if I have cancel_work_sync?
+	// FIXME: are all kfifo access secured by lock? with irq or not?
+	dev->reschedule_work = false;
+	/* Work not started at this point */
+	timer_setup(&dev->wakeup_timer, ft260_uart_start_wakeup, 0);
+
+	tty_port_init(&dev->port);
+	dev->port.ops = &ft260_uart_port_ops;
+
+	ret = ft260_uart_add_port(dev);
+	if (ret) {
+		hid_err(hdev, "failed to add port\n");
+		return ret;
+	}
+	devt = tty_port_register_device_attr(&dev->port,
+					     ft260_tty_driver,
+					     dev->index, &hdev->dev,
+					     dev, NULL);
+	if (IS_ERR(devt)) {
+		hid_err(hdev, "failed to register tty port\n");
+		ret = PTR_ERR(devt);
+		goto err_register_tty;
+	}
+	hid_info(hdev, "Registering device /dev/%s%d\n",
+		ft260_tty_driver->name, dev->index);
+
+	/* Send Feature Report to Configure FT260 as UART 9600-8-N-1 */
+	req.report	= FT260_SYSTEM_SETTINGS;
+	req.request	= FT260_SET_UART_CONFIG;
+	req.flow_ctrl	= FT260_CFG_FLOW_CTRL_NONE;
+	put_unaligned_le32(cpu_to_le32(9600), &req.baudrate);
+	req.data_bit	= FT260_CFG_DATA_BITS_8;
+	req.parity	= FT260_CFG_PAR_NO;
+	req.stop_bit	= FT260_CFG_STOP_ONE_BIT;
+	req.breaking	= FT260_CFG_BREAKING_NO;
+
+	ret = ft260_hid_feature_report_set(hdev, (u8 *)&req, sizeof(req));
+	if (ret < 0) {
+		hid_err(hdev, "ft260_hid_feature_report_set failed: %d\n",
+			ret);
+		goto err_hid_report;
+	}
+
+	return 0;
+
+err_hid_report:
+	tty_port_unregister_device(&dev->port, ft260_tty_driver, dev->index);
+err_register_tty:
+	ft260_uart_port_remove(dev);
+	return ret;
+}
+
 static int ft260_probe(struct hid_device *hdev, const struct hid_device_id *id)
 {
 	struct ft260_device *dev;
@@ -1010,20 +1676,26 @@ static int ft260_probe(struct hid_device *hdev, const struct hid_device_id *id)
 	if (!hid_is_usb(hdev))
 		return -EINVAL;
 
-	dev = devm_kzalloc(&hdev->dev, sizeof(*dev), GFP_KERNEL);
-	if (!dev)
-		return -ENOMEM;
+	/* We cannot used devm_kzalloc here, because port has to survive until
+	 * destroy function call
+	 */
+	dev = kzalloc_obj(*dev, GFP_KERNEL);
+	if (!dev) {
+		ret = -ENOMEM;
+		goto alloc_fail;
+	}
+	hid_set_drvdata(hdev, dev);
 
 	ret = hid_parse(hdev);
 	if (ret) {
 		hid_err(hdev, "failed to parse HID\n");
-		return ret;
+		goto hid_fail;
 	}
 
 	ret = hid_hw_start(hdev, 0);
 	if (ret) {
 		hid_err(hdev, "failed to start HID HW\n");
-		return ret;
+		goto hid_fail;
 	}
 
 	ret = hid_hw_open(hdev);
@@ -1043,53 +1715,36 @@ static int ft260_probe(struct hid_device *hdev, const struct hid_device_id *id)
 		 version.chip_code[0], version.chip_code[1],
 		 version.chip_code[2], version.chip_code[3]);
 
-	ret = ft260_is_interface_enabled(hdev);
-	if (ret <= 0)
+	ret = ft260_get_interface_type(hdev, dev);
+	if (ret <= FT260_IFACE_NONE)
 		goto err_hid_close;
 
-	hid_info(hdev, "USB HID v%x.%02x Device [%s] on %s\n",
-		hdev->version >> 8, hdev->version & 0xff, hdev->name,
-		hdev->phys);
-
 	hid_set_drvdata(hdev, dev);
 	dev->hdev = hdev;
-	dev->adap.owner = THIS_MODULE;
-	dev->adap.class = I2C_CLASS_HWMON;
-	dev->adap.algo = &ft260_i2c_algo;
-	dev->adap.quirks = &ft260_i2c_quirks;
-	dev->adap.dev.parent = &hdev->dev;
-	snprintf(dev->adap.name, sizeof(dev->adap.name),
-		 "FT260 usb-i2c bridge");
 
 	mutex_init(&dev->lock);
 	spin_lock_init(&dev->read_lock);
 	init_completion(&dev->wait);
 
-	ret = ft260_xfer_status(dev, FT260_I2C_STATUS_BUS_BUSY);
-	if (ret)
-		ft260_i2c_reset(hdev);
-
-	i2c_set_adapdata(&dev->adap, dev);
-	ret = i2c_add_adapter(&dev->adap);
-	if (ret) {
-		hid_err(hdev, "failed to add i2c adapter\n");
-		goto err_hid_close;
-	}
-
-	ret = sysfs_create_group(&hdev->dev.kobj, &ft260_attr_group);
-	if (ret < 0) {
-		hid_err(hdev, "failed to create sysfs attrs\n");
-		goto err_i2c_free;
+	if (!dev->ft260_is_serial) {
+		ret = ft260_i2c_probe(hdev, dev);
+		if (ret)
+			goto err_hid_close;
+	} else {
+		ret = ft260_uart_probe(hdev, dev);
+		if (ret)
+			goto err_hid_close;
 	}
 
 	return 0;
 
-err_i2c_free:
-	i2c_del_adapter(&dev->adap);
 err_hid_close:
 	hid_hw_close(hdev);
 err_hid_stop:
 	hid_hw_stop(hdev);
+hid_fail:
+	kfree(dev);
+alloc_fail:
 	return ret;
 }
 
@@ -1100,8 +1755,18 @@ static void ft260_remove(struct hid_device *hdev)
 	if (!dev)
 		return;
 
-	sysfs_remove_group(&hdev->dev.kobj, &ft260_attr_group);
-	i2c_del_adapter(&dev->adap);
+	if (dev->ft260_is_serial) {
+		// FIXME:
+		cancel_work_sync(&dev->wakeup_work);
+		tty_port_unregister_device(&dev->port, ft260_tty_driver,
+					   dev->index);
+		ft260_uart_port_remove(dev);
+		/* dev still needed, so we will free it in _destroy func */
+	} else {
+		sysfs_remove_group(&hdev->dev.kobj, &ft260_attr_group);
+		i2c_del_adapter(&dev->adap);
+		kfree(dev);
+	}
 
 	hid_hw_close(hdev);
 	hid_hw_stop(hdev);
@@ -1111,10 +1776,10 @@ static int ft260_raw_event(struct hid_device *hdev, struct hid_report *report,
 			   u8 *data, int size)
 {
 	struct ft260_device *dev = hid_get_drvdata(hdev);
-	struct ft260_i2c_input_report *xfer = (void *)data;
+	struct ft260_input_report *xfer = (void *)data;
 	unsigned long irqflags;
 
-	if (size < offsetof(struct ft260_i2c_input_report, data)) {
+	if (size < offsetof(struct ft260_input_report, data)) {
 		hid_err(hdev, "short report %d\n", size);
 		return -1;
 	}
@@ -1127,7 +1792,7 @@ static int ft260_raw_event(struct hid_device *hdev, struct hid_report *report,
 			  xfer->report, xfer->length, size);
 
 		if (xfer->length > size -
-		    offsetof(struct ft260_i2c_input_report, data)) {
+		    offsetof(struct ft260_input_report, data)) {
 			hid_err(hdev, "report %#02x: length %d exceeds HID report size\n",
 				xfer->report, xfer->length);
 			return -1;
@@ -1157,9 +1822,17 @@ static int ft260_raw_event(struct hid_device *hdev, struct hid_report *report,
 		if (complete_read)
 			complete(&dev->wait);
 
-	} else {
-		hid_err(hdev, "unhandled report %#02x\n", xfer->report);
+		return 0;
+
+	} else if (xfer->length > FT260_RD_DATA_MAX) {
+		hid_err(hdev, "received data too long (%d)\n", xfer->length);
+		return -EBADR;
+	} else if (xfer->report >= FT260_UART_REPORT_MIN &&
+		   xfer->report <= FT260_UART_REPORT_MAX) {
+		return ft260_uart_receive_chars(dev, xfer->data, xfer->length);
 	}
+	hid_err(hdev, "unhandled report %#02x\n", xfer->report);
+
 	return 0;
 }
 
@@ -1171,7 +1844,62 @@ static struct hid_driver ft260_driver = {
 	.raw_event	= ft260_raw_event,
 };
 
-module_hid_driver(ft260_driver);
-MODULE_DESCRIPTION("FTDI FT260 USB HID to I2C host bridge");
+static int __init ft260_driver_init(void)
+{
+	int ret;
+
+	ft260_tty_driver = tty_alloc_driver(UART_COUNT_MAX,
+		TTY_DRIVER_REAL_RAW | TTY_DRIVER_DYNAMIC_DEV);
+	if (IS_ERR(ft260_tty_driver)) {
+		pr_err("tty_alloc_driver failed: %d\n",
+			(int)PTR_ERR(ft260_tty_driver));
+		return PTR_ERR(ft260_tty_driver);
+	}
+
+	ft260_tty_driver->driver_name = "ft260_ser";
+	ft260_tty_driver->name = "ttyFT";
+	ft260_tty_driver->major = 0;
+	ft260_tty_driver->minor_start = 0;
+	ft260_tty_driver->type = TTY_DRIVER_TYPE_SERIAL;
+	ft260_tty_driver->subtype = SERIAL_TYPE_NORMAL;
+	ft260_tty_driver->init_termios = tty_std_termios;
+	ft260_tty_driver->init_termios.c_cflag = B9600 | CS8 | CREAD | HUPCL | CLOCAL;
+	ft260_tty_driver->init_termios.c_ispeed = 9600;
+	ft260_tty_driver->init_termios.c_ospeed = 9600;
+	tty_set_operations(ft260_tty_driver, &ft260_uart_ops);
+
+	ret = tty_register_driver(ft260_tty_driver);
+	if (ret) {
+		pr_err("tty_register_driver failed: %d\n", ret);
+		goto err_reg_driver;
+	}
+
+	ret = hid_register_driver(&(ft260_driver));
+	if (ret) {
+		pr_err("hid_register_driver failed: %d\n", ret);
+		goto err_reg_hid;
+	}
+
+	return 0;
+
+err_reg_hid:
+	tty_unregister_driver(ft260_tty_driver);
+err_reg_driver:
+	tty_driver_kref_put(ft260_tty_driver);
+
+	return ret;
+}
+
+static void __exit ft260_driver_exit(void)
+{
+	hid_unregister_driver(&(ft260_driver));
+	tty_unregister_driver(ft260_tty_driver);
+	tty_driver_kref_put(ft260_tty_driver);
+}
+
+module_init(ft260_driver_init);
+module_exit(ft260_driver_exit);
+
+MODULE_DESCRIPTION("FTDI FT260 USB HID to I2C host bridge and TTY driver");
 MODULE_AUTHOR("Michael Zaidman <michael.zaidman@xxxxxxxxx>");
 MODULE_LICENSE("GPL v2");
-- 
2.43.0