linux/drivers/usb/serial/ark3116.c
Greg Kroah-Hartman e5b1e2062e USB: serial: make minor allocation dynamic
This moves the allocation of minor device numbers from a static array to
be dynamic, using the idr interface.  This means that you could
potentially get "gaps" in a minor number range for a single USB serial
device with multiple ports, but all should still work properly.

We remove the 'minor' field from the usb_serial structure, as it no
longer makes any sense for it (use the field in the usb_serial_port
structure if you really want to know this number), and take the fact
that we were overloading a number in this field to determine if we had
initialized the minor numbers or not, and just use a flag variable
instead.

Note, we still have the limitation of 255 USB to serial devices in the
system, as that is all we are registering with the TTY layer at this
point in time.

Tested-by: Tobias Winter <tobias@linuxdingsda.de>
Reviewed-by: Johan Hovold <jhovold@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2013-06-17 13:30:02 -07:00

793 lines
21 KiB
C

/*
* 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>
#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 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)
{
/* 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;
}
return 0;
}
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(&serial->dev->dev,
"%s using %s mode\n",
KBUILD_MODNAME,
priv->irda ? "IrDA" : "RS232");
return 0;
}
static int 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);
return 0;
}
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;
/* 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_ioctl(struct tty_struct *tty,
unsigned int cmd, unsigned long arg)
{
struct usb_serial_port *port = tty->driver_data;
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->minor;
serstruct.port = 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;
}
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)
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(&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);
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,
.attach = ark3116_attach,
.port_probe = ark3116_port_probe,
.port_remove = ark3116_port_remove,
.set_termios = ark3116_set_termios,
.init_termios = ark3116_init_termios,
.ioctl = ark3116_ioctl,
.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
* (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
*/