/*
* 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.
*
* This program is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License as published by the
* Free Software Foundation; either version 2 of the License, or (at your
* option) any later version.
*/
#include <linux/kernel.h>
#include <linux/init.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>
static bool debug;
/*
* Version information
*/
#define DRIVER_VERSION "v0.7"
#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 (1*HZ)
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 {
wait_queue_head_t delta_msr_wait;
struct async_icount icount;
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 contol 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);
return result;
}
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 < 0)
return result;
else
return buf[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_attach(struct usb_serial *serial)
{
struct usb_serial_port *port = serial->port[0];
struct ark3116_private *priv;
/* make sure we have our end-points */
if ((serial->num_bulk_in == 0) ||
(serial->num_bulk_out == 0) ||
(serial->num_interrupt_in == 0)) {
dev_err(&serial->dev->dev,
"%s - missing endpoint - "
"bulk in: %d, bulk out: %d, int in %d\n",
KBUILD_MODNAME,
serial->num_bulk_in,
serial->num_bulk_out,
serial->num_interrupt_in);
return -EINVAL;
}
priv = kzalloc(sizeof(struct ark3116_private),
GFP_KERNEL);
if (!priv)
return -ENOMEM;
init_waitqueue_head(&priv->delta_msr_wait);
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(&serial->dev->dev,
"%s using %s mode\n",
KBUILD_MODNAME,
priv->irda ? "IrDA" : "RS232");
return 0;
}
static void ark3116_release(struct usb_serial *serial)
{
struct usb_serial_port *port = serial->port[0];
struct ark3116_private *priv = usb_get_serial_port_data(port);
/* device is closed, so URBs and DMA should be down */
usb_set_serial_port_data(port, NULL);
mutex_destroy(&priv->hw_lock);
kfree(priv);
}
static void ark3116_init_termios(struct tty_struct *tty)
{
struct ktermios *termios = tty->termios;
*termios = tty_std_termios;
termios->c_cflag = B9600 | CS8
| CREAD | HUPCL | CLOCAL;
termios->c_ispeed = 9600;
termios->c_ospeed = 9600;
}
static void ark3116_set_termios(struct tty_struct *tty,
struct usb_serial_port *port,
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 */
switch (cflag & CSIZE) {
case CS5:
lcr = UART_LCR_WLEN5;
break;
case CS6:
lcr = UART_LCR_WLEN6;
break;
case CS7:
lcr = UART_LCR_WLEN7;
break;
default:
case CS8:
lcr = UART_LCR_WLEN8;
break;
}
if (cflag & CSTOPB)
lcr |= UART_LCR_STOP;
if (cflag & PARENB)
lcr |= UART_LCR_PARITY;
if (!(cflag & PARODD))
lcr |= UART_LCR_EPAR;
#ifdef CMSPAR
if (cflag & CMSPAR)
lcr |= UART_LCR_SPAR;
#endif
/* 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(&serial->dev->dev,
"%s: don't know how to do software flow control\n",
KBUILD_MODNAME);
}
/* 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;
if (serial->dev) {
/* disable DMA */
ark3116_write_reg(serial, UART_FCR, 0);
/* deactivate interrupts */
ark3116_write_reg(serial, UART_IER, 0);
usb_serial_generic_close(port);
if (serial->num_interrupt_in)
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_out;
}
/* remove any data still left: also clears error state */
ark3116_read_reg(serial, UART_RX, buf);
/* read modem status */
priv->msr = ark3116_read_reg(serial, UART_MSR, buf);
/* read line status */
priv->lsr = ark3116_read_reg(serial, UART_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);
ark3116_close(port);
goto err_out;
}
/* 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);
err_out:
kfree(buf);
return result;
}
static int ark3116_get_icount(struct tty_struct *tty,
struct serial_icounter_struct *icount)
{
struct usb_serial_port *port = tty->driver_data;
struct ark3116_private *priv = usb_get_serial_port_data(port);
struct async_icount cnow = priv->icount;
icount->cts = cnow.cts;
icount->dsr = cnow.dsr;
icount->rng = cnow.rng;
icount->dcd = cnow.dcd;
icount->rx = cnow.rx;
icount->tx = cnow.tx;
icount->frame = cnow.frame;
icount->overrun = cnow.overrun;
icount->parity = cnow.parity;
icount->brk = cnow.brk;
icount->buf_overrun = cnow.buf_overrun;
return 0;
}
static int ark3116_ioctl(struct tty_struct *tty,
unsigned int cmd, unsigned long arg)
{
struct usb_serial_port *port = tty->driver_data;
struct ark3116_private *priv = usb_get_serial_port_data(port);
struct serial_struct serstruct;
void __user *user_arg = (void __user *)arg;
switch (cmd) {
case TIOCGSERIAL:
/* XXX: Some of these values are probably wrong. */
memset(&serstruct, 0, sizeof(serstruct));
serstruct.type = PORT_16654;
serstruct.line = port->serial->minor;
serstruct.port = port->number;
serstruct.custom_divisor = 0;
serstruct.baud_base = 460800;
if (copy_to_user(user_arg, &serstruct, sizeof(serstruct)))
return -EFAULT;
return 0;
case TIOCSSERIAL:
if (copy_from_user(&serstruct, user_arg, sizeof(serstruct)))
return -EFAULT;
return 0;
case TIOCMIWAIT:
for (;;) {
struct async_icount prev = priv->icount;
interruptible_sleep_on(&priv->delta_msr_wait);
/* see if a signal did it */
if (signal_pending(current))
return -ERESTARTSYS;
if ((prev.rng == priv->icount.rng) &&
(prev.dsr == priv->icount.dsr) &&
(prev.dcd == priv->icount.dcd) &&
(prev.cts == priv->icount.cts))
return -EIO;
if ((arg & TIOCM_RNG &&
(prev.rng != priv->icount.rng)) ||
(arg & TIOCM_DSR &&
(prev.dsr != priv->icount.dsr)) ||
(arg & TIOCM_CD &&
(prev.dcd != priv->icount.dcd)) ||
(arg & TIOCM_CTS &&
(prev.cts != priv->icount.cts)))
return 0;
}
break;
}
return -ENOIOCTLCMD;
}
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)
priv->icount.cts++;
if (msr & UART_MSR_DDSR)
priv->icount.dsr++;
if (msr & UART_MSR_DDCD)
priv->icount.dcd++;
if (msr & UART_MSR_TERI)
priv->icount.rng++;
wake_up_interruptible(&priv->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)
priv->icount.brk++;
if (lsr & UART_LSR_FE)
priv->icount.frame++;
if (lsr & UART_LSR_PE)
priv->icount.parity++;
if (lsr & UART_LSR_OE)
priv->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(debug, &port->dev,
__func__,
urb->actual_length,
urb->transfer_buffer);
break;
}
result = usb_submit_urb(urb, GFP_ATOMIC);
if (result)
dev_err(&urb->dev->dev,
"%s - Error %d submitting interrupt urb\n",
__func__, result);
}
/* Data comes in via the bulk (data) URB, erors/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);
struct tty_struct *tty;
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;
tty = tty_port_tty_get(&port->port);
if (!tty)
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(tty, 0, TTY_OVERRUN);
}
tty_insert_flip_string_fixed_flag(tty, data, tty_flag,
urb->actual_length);
tty_flip_buffer_push(tty);
tty_kref_put(tty);
}
static struct usb_serial_driver ark3116_device = {
.driver = {
.owner = THIS_MODULE,
.name = "ark3116",
},
.id_table = id_table,
.num_ports = 1,
.attach = ark3116_attach,
.release = ark3116_release,
.set_termios = ark3116_set_termios,
.init_termios = ark3116_init_termios,
.ioctl = ark3116_ioctl,
.tiocmget = ark3116_tiocmget,
.tiocmset = ark3116_tiocmset,
.get_icount = ark3116_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);
module_param(debug, bool, S_IRUGO | S_IWUSR);
MODULE_PARM_DESC(debug, "Enable debug");
/*
* 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
* (http://lkml.org/lkml/2009/7/26/56), 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
*/
