Adding upstream version 6.1.76.upstream/6.1.76upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 732 insertions, 0 deletions

diff --git a/drivers/usb/serial/ark3116.c b/drivers/usb/serial/ark3116.c
new file mode 100644
index 000000000..9452291f1
--- /dev/null
+++ b/drivers/usb/serial/ark3116.c
@@ -0,0 +1,732 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Copyright (C) 2009 by Bart Hartgers (bart.hartgers+ark3116@gmail.com)
+ * Original version:
+ * Copyright (C) 2006
+ *   Simon Schulz (ark3116_driver <at> auctionant.de)
+ *
+ * ark3116
+ * - implements a driver for the arkmicro ark3116 chipset (vendor=0x6547,
+ *   productid=0x0232) (used in a datacable called KQ-U8A)
+ *
+ * Supports full modem status lines, break, hardware flow control. Does not
+ * support software flow control, since I do not know how to enable it in hw.
+ *
+ * This driver is a essentially new implementation. I initially dug
+ * into the old ark3116.c driver and suddenly realized the ark3116 is
+ * a 16450 with a USB interface glued to it. See comments at the
+ * bottom of this file.
+ */
+
+#include <linux/kernel.h>
+#include <linux/ioctl.h>
+#include <linux/tty.h>
+#include <linux/slab.h>
+#include <linux/tty_flip.h>
+#include <linux/module.h>
+#include <linux/usb.h>
+#include <linux/usb/serial.h>
+#include <linux/serial.h>
+#include <linux/serial_reg.h>
+#include <linux/uaccess.h>
+#include <linux/mutex.h>
+#include <linux/spinlock.h>
+
+#define DRIVER_AUTHOR "Bart Hartgers <bart.hartgers+ark3116@gmail.com>"
+#define DRIVER_DESC "USB ARK3116 serial/IrDA driver"
+#define DRIVER_DEV_DESC "ARK3116 RS232/IrDA"
+#define DRIVER_NAME "ark3116"
+
+/* usb timeout of 1 second */
+#define ARK_TIMEOUT 1000
+
+static const struct usb_device_id id_table[] = {
+	{ USB_DEVICE(0x6547, 0x0232) },
+	{ USB_DEVICE(0x18ec, 0x3118) },		/* USB to IrDA adapter */
+	{ },
+};
+MODULE_DEVICE_TABLE(usb, id_table);
+
+static int is_irda(struct usb_serial *serial)
+{
+	struct usb_device *dev = serial->dev;
+	if (le16_to_cpu(dev->descriptor.idVendor) == 0x18ec &&
+			le16_to_cpu(dev->descriptor.idProduct) == 0x3118)
+		return 1;
+	return 0;
+}
+
+struct ark3116_private {
+	int			irda;	/* 1 for irda device */
+
+	/* protects hw register updates */
+	struct mutex		hw_lock;
+
+	int			quot;	/* baudrate divisor */
+	__u32			lcr;	/* line control register value */
+	__u32			hcr;	/* handshake control register (0x8)
+					 * value */
+	__u32			mcr;	/* modem control register value */
+
+	/* protects the status values below */
+	spinlock_t		status_lock;
+	__u32			msr;	/* modem status register value */
+	__u32			lsr;	/* line status register value */
+};
+
+static int ark3116_write_reg(struct usb_serial *serial,
+			     unsigned reg, __u8 val)
+{
+	int result;
+	 /* 0xfe 0x40 are magic values taken from original driver */
+	result = usb_control_msg(serial->dev,
+				 usb_sndctrlpipe(serial->dev, 0),
+				 0xfe, 0x40, val, reg,
+				 NULL, 0, ARK_TIMEOUT);
+	if (result)
+		return result;
+
+	return 0;
+}
+
+static int ark3116_read_reg(struct usb_serial *serial,
+			    unsigned reg, unsigned char *buf)
+{
+	int result;
+	/* 0xfe 0xc0 are magic values taken from original driver */
+	result = usb_control_msg(serial->dev,
+				 usb_rcvctrlpipe(serial->dev, 0),
+				 0xfe, 0xc0, 0, reg,
+				 buf, 1, ARK_TIMEOUT);
+	if (result < 1) {
+		dev_err(&serial->interface->dev,
+				"failed to read register %u: %d\n",
+				reg, result);
+		if (result >= 0)
+			result = -EIO;
+
+		return result;
+	}
+
+	return 0;
+}
+
+static inline int calc_divisor(int bps)
+{
+	/* Original ark3116 made some exceptions in rounding here
+	 * because windows did the same. Assume that is not really
+	 * necessary.
+	 * Crystal is 12MHz, probably because of USB, but we divide by 4?
+	 */
+	return (12000000 + 2*bps) / (4*bps);
+}
+
+static int ark3116_port_probe(struct usb_serial_port *port)
+{
+	struct usb_serial *serial = port->serial;
+	struct ark3116_private *priv;
+
+	priv = kzalloc(sizeof(*priv), GFP_KERNEL);
+	if (!priv)
+		return -ENOMEM;
+
+	mutex_init(&priv->hw_lock);
+	spin_lock_init(&priv->status_lock);
+
+	priv->irda = is_irda(serial);
+
+	usb_set_serial_port_data(port, priv);
+
+	/* setup the hardware */
+	ark3116_write_reg(serial, UART_IER, 0);
+	/* disable DMA */
+	ark3116_write_reg(serial, UART_FCR, 0);
+	/* handshake control */
+	priv->hcr = 0;
+	ark3116_write_reg(serial, 0x8     , 0);
+	/* modem control */
+	priv->mcr = 0;
+	ark3116_write_reg(serial, UART_MCR, 0);
+
+	if (!(priv->irda)) {
+		ark3116_write_reg(serial, 0xb , 0);
+	} else {
+		ark3116_write_reg(serial, 0xb , 1);
+		ark3116_write_reg(serial, 0xc , 0);
+		ark3116_write_reg(serial, 0xd , 0x41);
+		ark3116_write_reg(serial, 0xa , 1);
+	}
+
+	/* setup baudrate */
+	ark3116_write_reg(serial, UART_LCR, UART_LCR_DLAB);
+
+	/* setup for 9600 8N1 */
+	priv->quot = calc_divisor(9600);
+	ark3116_write_reg(serial, UART_DLL, priv->quot & 0xff);
+	ark3116_write_reg(serial, UART_DLM, (priv->quot>>8) & 0xff);
+
+	priv->lcr = UART_LCR_WLEN8;
+	ark3116_write_reg(serial, UART_LCR, UART_LCR_WLEN8);
+
+	ark3116_write_reg(serial, 0xe, 0);
+
+	if (priv->irda)
+		ark3116_write_reg(serial, 0x9, 0);
+
+	dev_info(&port->dev, "using %s mode\n", priv->irda ? "IrDA" : "RS232");
+
+	return 0;
+}
+
+static void ark3116_port_remove(struct usb_serial_port *port)
+{
+	struct ark3116_private *priv = usb_get_serial_port_data(port);
+
+	/* device is closed, so URBs and DMA should be down */
+	mutex_destroy(&priv->hw_lock);
+	kfree(priv);
+}
+
+static void ark3116_set_termios(struct tty_struct *tty,
+				struct usb_serial_port *port,
+				const struct ktermios *old_termios)
+{
+	struct usb_serial *serial = port->serial;
+	struct ark3116_private *priv = usb_get_serial_port_data(port);
+	struct ktermios *termios = &tty->termios;
+	unsigned int cflag = termios->c_cflag;
+	int bps = tty_get_baud_rate(tty);
+	int quot;
+	__u8 lcr, hcr, eval;
+
+	/* set data bit count */
+	lcr = UART_LCR_WLEN(tty_get_char_size(cflag));
+
+	if (cflag & CSTOPB)
+		lcr |= UART_LCR_STOP;
+	if (cflag & PARENB)
+		lcr |= UART_LCR_PARITY;
+	if (!(cflag & PARODD))
+		lcr |= UART_LCR_EPAR;
+	if (cflag & CMSPAR)
+		lcr |= UART_LCR_SPAR;
+
+	/* handshake control */
+	hcr = (cflag & CRTSCTS) ? 0x03 : 0x00;
+
+	/* calc baudrate */
+	dev_dbg(&port->dev, "%s - setting bps to %d\n", __func__, bps);
+	eval = 0;
+	switch (bps) {
+	case 0:
+		quot = calc_divisor(9600);
+		break;
+	default:
+		if ((bps < 75) || (bps > 3000000))
+			bps = 9600;
+		quot = calc_divisor(bps);
+		break;
+	case 460800:
+		eval = 1;
+		quot = calc_divisor(bps);
+		break;
+	case 921600:
+		eval = 2;
+		quot = calc_divisor(bps);
+		break;
+	}
+
+	/* Update state: synchronize */
+	mutex_lock(&priv->hw_lock);
+
+	/* keep old LCR_SBC bit */
+	lcr |= (priv->lcr & UART_LCR_SBC);
+
+	dev_dbg(&port->dev, "%s - setting hcr:0x%02x,lcr:0x%02x,quot:%d\n",
+		__func__, hcr, lcr, quot);
+
+	/* handshake control */
+	if (priv->hcr != hcr) {
+		priv->hcr = hcr;
+		ark3116_write_reg(serial, 0x8, hcr);
+	}
+
+	/* baudrate */
+	if (priv->quot != quot) {
+		priv->quot = quot;
+		priv->lcr = lcr; /* need to write lcr anyway */
+
+		/* disable DMA since transmit/receive is
+		 * shadowed by UART_DLL
+		 */
+		ark3116_write_reg(serial, UART_FCR, 0);
+
+		ark3116_write_reg(serial, UART_LCR,
+				  lcr|UART_LCR_DLAB);
+		ark3116_write_reg(serial, UART_DLL, quot & 0xff);
+		ark3116_write_reg(serial, UART_DLM, (quot>>8) & 0xff);
+
+		/* restore lcr */
+		ark3116_write_reg(serial, UART_LCR, lcr);
+		/* magic baudrate thingy: not sure what it does,
+		 * but windows does this as well.
+		 */
+		ark3116_write_reg(serial, 0xe, eval);
+
+		/* enable DMA */
+		ark3116_write_reg(serial, UART_FCR, UART_FCR_DMA_SELECT);
+	} else if (priv->lcr != lcr) {
+		priv->lcr = lcr;
+		ark3116_write_reg(serial, UART_LCR, lcr);
+	}
+
+	mutex_unlock(&priv->hw_lock);
+
+	/* check for software flow control */
+	if (I_IXOFF(tty) || I_IXON(tty)) {
+		dev_warn(&port->dev,
+				"software flow control not implemented\n");
+	}
+
+	/* Don't rewrite B0 */
+	if (tty_termios_baud_rate(termios))
+		tty_termios_encode_baud_rate(termios, bps, bps);
+}
+
+static void ark3116_close(struct usb_serial_port *port)
+{
+	struct usb_serial *serial = port->serial;
+
+	/* disable DMA */
+	ark3116_write_reg(serial, UART_FCR, 0);
+
+	/* deactivate interrupts */
+	ark3116_write_reg(serial, UART_IER, 0);
+
+	usb_serial_generic_close(port);
+
+	usb_kill_urb(port->interrupt_in_urb);
+}
+
+static int ark3116_open(struct tty_struct *tty, struct usb_serial_port *port)
+{
+	struct ark3116_private *priv = usb_get_serial_port_data(port);
+	struct usb_serial *serial = port->serial;
+	unsigned char *buf;
+	int result;
+
+	buf = kmalloc(1, GFP_KERNEL);
+	if (buf == NULL)
+		return -ENOMEM;
+
+	result = usb_serial_generic_open(tty, port);
+	if (result) {
+		dev_dbg(&port->dev,
+			"%s - usb_serial_generic_open failed: %d\n",
+			__func__, result);
+		goto err_free;
+	}
+
+	/* remove any data still left: also clears error state */
+	ark3116_read_reg(serial, UART_RX, buf);
+
+	/* read modem status */
+	result = ark3116_read_reg(serial, UART_MSR, buf);
+	if (result)
+		goto err_close;
+	priv->msr = *buf;
+
+	/* read line status */
+	result = ark3116_read_reg(serial, UART_LSR, buf);
+	if (result)
+		goto err_close;
+	priv->lsr = *buf;
+
+	result = usb_submit_urb(port->interrupt_in_urb, GFP_KERNEL);
+	if (result) {
+		dev_err(&port->dev, "submit irq_in urb failed %d\n",
+			result);
+		goto err_close;
+	}
+
+	/* activate interrupts */
+	ark3116_write_reg(port->serial, UART_IER, UART_IER_MSI|UART_IER_RLSI);
+
+	/* enable DMA */
+	ark3116_write_reg(port->serial, UART_FCR, UART_FCR_DMA_SELECT);
+
+	/* setup termios */
+	if (tty)
+		ark3116_set_termios(tty, port, NULL);
+
+	kfree(buf);
+
+	return 0;
+
+err_close:
+	usb_serial_generic_close(port);
+err_free:
+	kfree(buf);
+
+	return result;
+}
+
+static int ark3116_tiocmget(struct tty_struct *tty)
+{
+	struct usb_serial_port *port = tty->driver_data;
+	struct ark3116_private *priv = usb_get_serial_port_data(port);
+	__u32 status;
+	__u32 ctrl;
+	unsigned long flags;
+
+	mutex_lock(&priv->hw_lock);
+	ctrl = priv->mcr;
+	mutex_unlock(&priv->hw_lock);
+
+	spin_lock_irqsave(&priv->status_lock, flags);
+	status = priv->msr;
+	spin_unlock_irqrestore(&priv->status_lock, flags);
+
+	return  (status & UART_MSR_DSR  ? TIOCM_DSR  : 0) |
+		(status & UART_MSR_CTS  ? TIOCM_CTS  : 0) |
+		(status & UART_MSR_RI   ? TIOCM_RI   : 0) |
+		(status & UART_MSR_DCD  ? TIOCM_CD   : 0) |
+		(ctrl   & UART_MCR_DTR  ? TIOCM_DTR  : 0) |
+		(ctrl   & UART_MCR_RTS  ? TIOCM_RTS  : 0) |
+		(ctrl   & UART_MCR_OUT1 ? TIOCM_OUT1 : 0) |
+		(ctrl   & UART_MCR_OUT2 ? TIOCM_OUT2 : 0);
+}
+
+static int ark3116_tiocmset(struct tty_struct *tty,
+			unsigned set, unsigned clr)
+{
+	struct usb_serial_port *port = tty->driver_data;
+	struct ark3116_private *priv = usb_get_serial_port_data(port);
+
+	/* we need to take the mutex here, to make sure that the value
+	 * in priv->mcr is actually the one that is in the hardware
+	 */
+
+	mutex_lock(&priv->hw_lock);
+
+	if (set & TIOCM_RTS)
+		priv->mcr |= UART_MCR_RTS;
+	if (set & TIOCM_DTR)
+		priv->mcr |= UART_MCR_DTR;
+	if (set & TIOCM_OUT1)
+		priv->mcr |= UART_MCR_OUT1;
+	if (set & TIOCM_OUT2)
+		priv->mcr |= UART_MCR_OUT2;
+	if (clr & TIOCM_RTS)
+		priv->mcr &= ~UART_MCR_RTS;
+	if (clr & TIOCM_DTR)
+		priv->mcr &= ~UART_MCR_DTR;
+	if (clr & TIOCM_OUT1)
+		priv->mcr &= ~UART_MCR_OUT1;
+	if (clr & TIOCM_OUT2)
+		priv->mcr &= ~UART_MCR_OUT2;
+
+	ark3116_write_reg(port->serial, UART_MCR, priv->mcr);
+
+	mutex_unlock(&priv->hw_lock);
+
+	return 0;
+}
+
+static void ark3116_break_ctl(struct tty_struct *tty, int break_state)
+{
+	struct usb_serial_port *port = tty->driver_data;
+	struct ark3116_private *priv = usb_get_serial_port_data(port);
+
+	/* LCR is also used for other things: protect access */
+	mutex_lock(&priv->hw_lock);
+
+	if (break_state)
+		priv->lcr |= UART_LCR_SBC;
+	else
+		priv->lcr &= ~UART_LCR_SBC;
+
+	ark3116_write_reg(port->serial, UART_LCR, priv->lcr);
+
+	mutex_unlock(&priv->hw_lock);
+}
+
+static void ark3116_update_msr(struct usb_serial_port *port, __u8 msr)
+{
+	struct ark3116_private *priv = usb_get_serial_port_data(port);
+	unsigned long flags;
+
+	spin_lock_irqsave(&priv->status_lock, flags);
+	priv->msr = msr;
+	spin_unlock_irqrestore(&priv->status_lock, flags);
+
+	if (msr & UART_MSR_ANY_DELTA) {
+		/* update input line counters */
+		if (msr & UART_MSR_DCTS)
+			port->icount.cts++;
+		if (msr & UART_MSR_DDSR)
+			port->icount.dsr++;
+		if (msr & UART_MSR_DDCD)
+			port->icount.dcd++;
+		if (msr & UART_MSR_TERI)
+			port->icount.rng++;
+		wake_up_interruptible(&port->port.delta_msr_wait);
+	}
+}
+
+static void ark3116_update_lsr(struct usb_serial_port *port, __u8 lsr)
+{
+	struct ark3116_private *priv = usb_get_serial_port_data(port);
+	unsigned long flags;
+
+	spin_lock_irqsave(&priv->status_lock, flags);
+	/* combine bits */
+	priv->lsr |= lsr;
+	spin_unlock_irqrestore(&priv->status_lock, flags);
+
+	if (lsr&UART_LSR_BRK_ERROR_BITS) {
+		if (lsr & UART_LSR_BI)
+			port->icount.brk++;
+		if (lsr & UART_LSR_FE)
+			port->icount.frame++;
+		if (lsr & UART_LSR_PE)
+			port->icount.parity++;
+		if (lsr & UART_LSR_OE)
+			port->icount.overrun++;
+	}
+}
+
+static void ark3116_read_int_callback(struct urb *urb)
+{
+	struct usb_serial_port *port = urb->context;
+	int status = urb->status;
+	const __u8 *data = urb->transfer_buffer;
+	int result;
+
+	switch (status) {
+	case -ECONNRESET:
+	case -ENOENT:
+	case -ESHUTDOWN:
+		/* this urb is terminated, clean up */
+		dev_dbg(&port->dev, "%s - urb shutting down with status: %d\n",
+			__func__, status);
+		return;
+	default:
+		dev_dbg(&port->dev, "%s - nonzero urb status received: %d\n",
+			__func__, status);
+		break;
+	case 0: /* success */
+		/* discovered this by trail and error... */
+		if ((urb->actual_length == 4) && (data[0] == 0xe8)) {
+			const __u8 id = data[1]&UART_IIR_ID;
+			dev_dbg(&port->dev, "%s: iir=%02x\n", __func__, data[1]);
+			if (id == UART_IIR_MSI) {
+				dev_dbg(&port->dev, "%s: msr=%02x\n",
+					__func__, data[3]);
+				ark3116_update_msr(port, data[3]);
+				break;
+			} else if (id == UART_IIR_RLSI) {
+				dev_dbg(&port->dev, "%s: lsr=%02x\n",
+					__func__, data[2]);
+				ark3116_update_lsr(port, data[2]);
+				break;
+			}
+		}
+		/*
+		 * Not sure what this data meant...
+		 */
+		usb_serial_debug_data(&port->dev, __func__,
+				      urb->actual_length,
+				      urb->transfer_buffer);
+		break;
+	}
+
+	result = usb_submit_urb(urb, GFP_ATOMIC);
+	if (result)
+		dev_err(&port->dev, "failed to resubmit interrupt urb: %d\n",
+			result);
+}
+
+
+/* Data comes in via the bulk (data) URB, errors/interrupts via the int URB.
+ * This means that we cannot be sure which data byte has an associated error
+ * condition, so we report an error for all data in the next bulk read.
+ *
+ * Actually, there might even be a window between the bulk data leaving the
+ * ark and reading/resetting the lsr in the read_bulk_callback where an
+ * interrupt for the next data block could come in.
+ * Without somekind of ordering on the ark, we would have to report the
+ * error for the next block of data as well...
+ * For now, let's pretend this can't happen.
+ */
+static void ark3116_process_read_urb(struct urb *urb)
+{
+	struct usb_serial_port *port = urb->context;
+	struct ark3116_private *priv = usb_get_serial_port_data(port);
+	unsigned char *data = urb->transfer_buffer;
+	char tty_flag = TTY_NORMAL;
+	unsigned long flags;
+	__u32 lsr;
+
+	/* update line status */
+	spin_lock_irqsave(&priv->status_lock, flags);
+	lsr = priv->lsr;
+	priv->lsr &= ~UART_LSR_BRK_ERROR_BITS;
+	spin_unlock_irqrestore(&priv->status_lock, flags);
+
+	if (!urb->actual_length)
+		return;
+
+	if (lsr & UART_LSR_BRK_ERROR_BITS) {
+		if (lsr & UART_LSR_BI)
+			tty_flag = TTY_BREAK;
+		else if (lsr & UART_LSR_PE)
+			tty_flag = TTY_PARITY;
+		else if (lsr & UART_LSR_FE)
+			tty_flag = TTY_FRAME;
+
+		/* overrun is special, not associated with a char */
+		if (lsr & UART_LSR_OE)
+			tty_insert_flip_char(&port->port, 0, TTY_OVERRUN);
+	}
+	tty_insert_flip_string_fixed_flag(&port->port, data, tty_flag,
+							urb->actual_length);
+	tty_flip_buffer_push(&port->port);
+}
+
+static struct usb_serial_driver ark3116_device = {
+	.driver = {
+		.owner =	THIS_MODULE,
+		.name =		"ark3116",
+	},
+	.id_table =		id_table,
+	.num_ports =		1,
+	.num_bulk_in =		1,
+	.num_bulk_out =		1,
+	.num_interrupt_in =	1,
+	.port_probe =		ark3116_port_probe,
+	.port_remove =		ark3116_port_remove,
+	.set_termios =		ark3116_set_termios,
+	.tiocmget =		ark3116_tiocmget,
+	.tiocmset =		ark3116_tiocmset,
+	.tiocmiwait =		usb_serial_generic_tiocmiwait,
+	.get_icount =		usb_serial_generic_get_icount,
+	.open =			ark3116_open,
+	.close =		ark3116_close,
+	.break_ctl = 		ark3116_break_ctl,
+	.read_int_callback = 	ark3116_read_int_callback,
+	.process_read_urb =	ark3116_process_read_urb,
+};
+
+static struct usb_serial_driver * const serial_drivers[] = {
+	&ark3116_device, NULL
+};
+
+module_usb_serial_driver(serial_drivers, id_table);
+
+MODULE_LICENSE("GPL");
+
+MODULE_AUTHOR(DRIVER_AUTHOR);
+MODULE_DESCRIPTION(DRIVER_DESC);
+
+/*
+ * The following describes what I learned from studying the old
+ * ark3116.c driver, disassembling the windows driver, and some lucky
+ * guesses. Since I do not have any datasheet or other
+ * documentation, inaccuracies are almost guaranteed.
+ *
+ * Some specs for the ARK3116 can be found here:
+ * http://web.archive.org/web/20060318000438/
+ *   www.arkmicro.com/en/products/view.php?id=10
+ * On that page, 2 GPIO pins are mentioned: I assume these are the
+ * OUT1 and OUT2 pins of the UART, so I added support for those
+ * through the MCR. Since the pins are not available on my hardware,
+ * I could not verify this.
+ * Also, it states there is "on-chip hardware flow control". I have
+ * discovered how to enable that. Unfortunately, I do not know how to
+ * enable XON/XOFF (software) flow control, which would need support
+ * from the chip as well to work. Because of the wording on the web
+ * page there is a real possibility the chip simply does not support
+ * software flow control.
+ *
+ * I got my ark3116 as part of a mobile phone adapter cable. On the
+ * PCB, the following numbered contacts are present:
+ *
+ *  1:- +5V
+ *  2:o DTR
+ *  3:i RX
+ *  4:i DCD
+ *  5:o RTS
+ *  6:o TX
+ *  7:i RI
+ *  8:i DSR
+ * 10:- 0V
+ * 11:i CTS
+ *
+ * On my chip, all signals seem to be 3.3V, but 5V tolerant. But that
+ * may be different for the one you have ;-).
+ *
+ * The windows driver limits the registers to 0-F, so I assume there
+ * are actually 16 present on the device.
+ *
+ * On an UART interrupt, 4 bytes of data come in on the interrupt
+ * endpoint. The bytes are 0xe8 IIR LSR MSR.
+ *
+ * The baudrate seems to be generated from the 12MHz crystal, using
+ * 4-times subsampling. So quot=12e6/(4*baud). Also see description
+ * of register E.
+ *
+ * Registers 0-7:
+ * These seem to be the same as for a regular 16450. The FCR is set
+ * to UART_FCR_DMA_SELECT (0x8), I guess to enable transfers between
+ * the UART and the USB bridge/DMA engine.
+ *
+ * Register 8:
+ * By trial and error, I found out that bit 0 enables hardware CTS,
+ * stopping TX when CTS is +5V. Bit 1 does the same for RTS, making
+ * RTS +5V when the 3116 cannot transfer the data to the USB bus
+ * (verified by disabling the reading URB). Note that as far as I can
+ * tell, the windows driver does NOT use this, so there might be some
+ * hardware bug or something.
+ *
+ * According to a patch provided here
+ * https://lore.kernel.org/lkml/200907261419.50702.linux@rainbow-software.org
+ * the ARK3116 can also be used as an IrDA dongle. Since I do not have
+ * such a thing, I could not investigate that aspect. However, I can
+ * speculate ;-).
+ *
+ * - IrDA encodes data differently than RS232. Most likely, one of
+ *   the bits in registers 9..E enables the IR ENDEC (encoder/decoder).
+ * - Depending on the IR transceiver, the input and output need to be
+ *   inverted, so there are probably bits for that as well.
+ * - IrDA is half-duplex, so there should be a bit for selecting that.
+ *
+ * This still leaves at least two registers unaccounted for. Perhaps
+ * The chip can do XON/XOFF or CRC in HW?
+ *
+ * Register 9:
+ * Set to 0x00 for IrDA, when the baudrate is initialised.
+ *
+ * Register A:
+ * Set to 0x01 for IrDA, at init.
+ *
+ * Register B:
+ * Set to 0x01 for IrDA, 0x00 for RS232, at init.
+ *
+ * Register C:
+ * Set to 00 for IrDA, at init.
+ *
+ * Register D:
+ * Set to 0x41 for IrDA, at init.
+ *
+ * Register E:
+ * Somekind of baudrate override. The windows driver seems to set
+ * this to 0x00 for normal baudrates, 0x01 for 460800, 0x02 for 921600.
+ * Since 460800 and 921600 cannot be obtained by dividing 3MHz by an integer,
+ * it could be somekind of subdivisor thingy.
+ * However,it does not seem to do anything: selecting 921600 (divisor 3,
+ * reg E=2), still gets 1 MHz. I also checked if registers 9, C or F would
+ * work, but they don't.
+ *
+ * Register F: unknown
+ */