source: mainline/uspace/drv/ns8250/ns8250.c@ c8dd5b1

/*
 * Copyright (c) 2010 Lenka Trochtova
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * - Redistributions of source code must retain the above copyright
 *   notice, this list of conditions and the following disclaimer.
 * - Redistributions in binary form must reproduce the above copyright
 *   notice, this list of conditions and the following disclaimer in the
 *   documentation and/or other materials provided with the distribution.
 * - The name of the author may not be used to endorse or promote products
 *   derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

/**
 * @defgroup ns8250 Serial port driver.
 * @brief HelenOS serial port driver.
 * @{
 */

/** @file
 */

#include <assert.h>
#include <stdio.h>
#include <errno.h>
#include <bool.h>
#include <fibril_synch.h>
#include <stdlib.h>
#include <str.h>
#include <ctype.h>
#include <macros.h>
#include <malloc.h>
#include <dirent.h>
#include <fcntl.h>
#include <sys/stat.h>
#include <ddi.h>
#include <libarch/ddi.h>

#include <driver.h>
#include <ops/char_dev.h>

#include <devman.h>
#include <ipc/devman.h>
#include <device/hw_res.h>
#include <ipc/serial_ctl.h>

#include "cyclic_buffer.h"

#define NAME "ns8250"

#define REG_COUNT 7
#define MAX_BAUD_RATE 115200
#define DLAB_MASK (1 << 7)

/** The number of bits of one data unit send by the serial port. */
typedef enum {
        WORD_LENGTH_5,
        WORD_LENGTH_6,
        WORD_LENGTH_7,
        WORD_LENGTH_8
} word_length_t;

/** The number of stop bits used by the serial port. */
typedef enum {
        /** Use one stop bit. */
        ONE_STOP_BIT,
        /** 1.5 stop bits for word length 5, 2 stop bits otherwise. */
        TWO_STOP_BITS
} stop_bit_t;

/** The driver data for the serial port devices. */
typedef struct ns8250_dev_data {
        /** Is there any client conntected to the device? */
        bool client_connected;
        /** The irq assigned to this device. */
        int irq;
        /** The base i/o address of the devices registers. */
        uint32_t io_addr;
        /** The i/o port used to access the serial ports registers. */
        ioport8_t *port;
        /** The buffer for incomming data. */
        cyclic_buffer_t input_buffer;
        /** The fibril mutex for synchronizing the access to the device. */
        fibril_mutex_t mutex;
} ns8250_dev_data_t;

/** Create driver data for a device.
 *
 * @return              The driver data.
 */
static ns8250_dev_data_t *create_ns8250_dev_data(void)
{
        ns8250_dev_data_t *data;
        
        data = (ns8250_dev_data_t *) malloc(sizeof(ns8250_dev_data_t));
        if (NULL != data) {
                memset(data, 0, sizeof(ns8250_dev_data_t));
                fibril_mutex_initialize(&data->mutex);
        }
        return data;
}

/** Delete driver data.
 *
 * @param data          The driver data structure.
 */
static void delete_ns8250_dev_data(ns8250_dev_data_t *data)
{
        if (data != NULL)
                free(data);
}

/** Find out if there is some incomming data available on the serial port.
 *
 * @param port          The base address of the serial port device's ports.
 * @return              True if there are data waiting to be read, false
 *                      otherwise.
 */
static bool ns8250_received(ioport8_t *port)
{
        return (pio_read_8(port + 5) & 1) != 0;
}

/** Read one byte from the serial port.
 *
 * @param port          The base address of the serial port device's ports.
 * @return              The data read.
 */
static uint8_t ns8250_read_8(ioport8_t *port)
{
        return pio_read_8(port);
}

/** Find out wheter it is possible to send data.
 *
 * @param port          The base address of the serial port device's ports.
 */
static bool is_transmit_empty(ioport8_t *port)
{
        return (pio_read_8(port + 5) & 0x20) != 0;
}

/** Write one character on the serial port.
 *
 * @param port          The base address of the serial port device's ports.
 * @param c             The character to be written to the serial port device.
 */
static void ns8250_write_8(ioport8_t *port, uint8_t c)
{
        while (!is_transmit_empty(port))
                ;
        
        pio_write_8(port, c);
}

/** Read data from the serial port device.
 *
 * @param dev           The serial port device.
 * @param buf           The ouput buffer for read data.
 * @param count         The number of bytes to be read.
 *
 * @return              The number of bytes actually read on success, negative
 *                      error number otherwise.
 */
static int ns8250_read(device_t *dev, char *buf, size_t count)
{
        int ret = EOK;
        ns8250_dev_data_t *data = (ns8250_dev_data_t *) dev->driver_data;
        
        fibril_mutex_lock(&data->mutex);
        while (!buf_is_empty(&data->input_buffer) && (size_t)ret < count) {
                buf[ret] = (char)buf_pop_front(&data->input_buffer);
                ret++;
        }
        fibril_mutex_unlock(&data->mutex);
        
        return ret;
}

/** Write a character to the serial port.
 *
 * @param data          The serial port device's driver data.
 * @param c             The character to be written.
 */
static inline void ns8250_putchar(ns8250_dev_data_t *data, uint8_t c)
{
        fibril_mutex_lock(&data->mutex);
        ns8250_write_8(data->port, c);
        fibril_mutex_unlock(&data->mutex);
}

/** Write data to the serial port.
 *
 * @param dev           The serial port device.
 * @param buf           The data to be written.
 * @param count         The number of bytes to be written.
 * @return              Zero on success.
 */
static int ns8250_write(device_t *dev, char *buf, size_t count) 
{
        ns8250_dev_data_t *data = (ns8250_dev_data_t *) dev->driver_data;
        size_t idx;
        
        for (idx = 0; idx < count; idx++)
                ns8250_putchar(data, (uint8_t) buf[idx]);
        
        return 0;
}

static device_ops_t ns8250_dev_ops;

/** The character interface's callbacks. */
static char_dev_ops_t ns8250_char_dev_ops = {
        .read = &ns8250_read,
        .write = &ns8250_write
};

static int ns8250_add_device(device_t *dev);

/** The serial port device driver's standard operations. */
static driver_ops_t ns8250_ops = {
        .add_device = &ns8250_add_device
};

/** The serial port device driver structure. */
static driver_t ns8250_driver = {
        .name = NAME,
        .driver_ops = &ns8250_ops
};

/** Clean up the serial port device structure.
 *
 * @param dev           The device structure.
 */
static void ns8250_dev_cleanup(device_t *dev)
{
        if (dev->driver_data != NULL) {
                delete_ns8250_dev_data((ns8250_dev_data_t*) dev->driver_data);
                dev->driver_data = NULL;
        }
        
        if (dev->parent_phone > 0) {
                async_hangup(dev->parent_phone);
                dev->parent_phone = 0;
        }
}

/** Enable the i/o ports of the device.
 *
 * @param dev           The serial port device.
 * @return              True on success, false otherwise.
 */
static bool ns8250_pio_enable(device_t *dev)
{
        printf(NAME ": ns8250_pio_enable %s\n", dev->name);
        
        ns8250_dev_data_t *data = (ns8250_dev_data_t *)dev->driver_data;
        
        /* Gain control over port's registers. */
        if (pio_enable((void *)(uintptr_t) data->io_addr, REG_COUNT,
            (void **) &data->port)) {
                printf(NAME ": error - cannot gain the port %#" PRIx32 " for device "
                    "%s.\n", data->io_addr, dev->name);
                return false;
        }
        
        return true;
}

/** Probe the serial port device for its presence.
 *
 * @param dev           The serial port device.
 * @return              True if the device is present, false otherwise.
 */
static bool ns8250_dev_probe(device_t *dev)
{
        printf(NAME ": ns8250_dev_probe %s\n", dev->name);
        
        ns8250_dev_data_t *data = (ns8250_dev_data_t *) dev->driver_data;
        ioport8_t *port_addr = data->port;
        bool res = true;
        uint8_t olddata;
        
        olddata = pio_read_8(port_addr + 4);
        
        pio_write_8(port_addr + 4, 0x10);
        if (pio_read_8(port_addr + 6) & 0xf0)
                res = false;
        
        pio_write_8(port_addr + 4, 0x1f);
        if ((pio_read_8(port_addr + 6) & 0xf0) != 0xf0)
                res = false;
        
        pio_write_8(port_addr + 4, olddata);
        
        if (!res)
                printf(NAME ": device %s is not present.\n", dev->name);
        
        return res;
}

/** Initialize serial port device.
 *
 * @param dev           The serial port device.
 * @return              Zero on success, negative error number otherwise.
 */
static int ns8250_dev_initialize(device_t *dev)
{
        printf(NAME ": ns8250_dev_initialize %s\n", dev->name);
        
        int ret = EOK;
        
        hw_resource_list_t hw_resources;
        memset(&hw_resources, 0, sizeof(hw_resource_list_t));
        
        /* Allocate driver data for the device. */
        ns8250_dev_data_t *data = create_ns8250_dev_data();
        if (data == NULL)
                return ENOMEM;
        dev->driver_data = data;
        
        /* Connect to the parent's driver. */
        dev->parent_phone = devman_parent_device_connect(dev->handle,
            IPC_FLAG_BLOCKING);
        if (dev->parent_phone < 0) {
                printf(NAME ": failed to connect to the parent driver of the "
                    "device %s.\n", dev->name);
                ret = dev->parent_phone;
                goto failed;
        }
        
        /* Get hw resources. */
        ret = hw_res_get_resource_list(dev->parent_phone, &hw_resources);
        if (ret != EOK) {
                printf(NAME ": failed to get hw resources for the device "
                    "%s.\n", dev->name);
                goto failed;
        }
        
        size_t i;
        hw_resource_t *res;
        bool irq = false;
        bool ioport = false;
        
        for (i = 0; i < hw_resources.count; i++) {
                res = &hw_resources.resources[i];
                switch (res->type) {
                case INTERRUPT:
                        data->irq = res->res.interrupt.irq;
                        irq = true;
                        printf(NAME ": the %s device was asigned irq = 0x%x.\n",
                            dev->name, data->irq);
                        break;
                        
                case IO_RANGE:
                        data->io_addr = res->res.io_range.address;
                        if (res->res.io_range.size < REG_COUNT) {
                                printf(NAME ": i/o range assigned to the device "
                                    "%s is too small.\n", dev->name);
                                ret = ELIMIT;
                                goto failed;
                        }
                        ioport = true;
                        printf(NAME ": the %s device was asigned i/o address = "
                            "0x%x.\n", dev->name, data->io_addr);
                        break;
                        
                default:
                        break;
                }
        }
        
        if (!irq || !ioport) {
                printf(NAME ": missing hw resource(s) for the device %s.\n",
                    dev->name);
                ret = ENOENT;
                goto failed;
        }
        
        hw_res_clean_resource_list(&hw_resources);
        return ret;
        
failed:
        ns8250_dev_cleanup(dev);
        hw_res_clean_resource_list(&hw_resources);
        return ret;
}

/** Enable interrupts on the serial port device.
 *
 * Interrupt when data is received.
 *
 * @param port          The base address of the serial port device's ports.
 */
static inline void ns8250_port_interrupts_enable(ioport8_t *port)
{       
        pio_write_8(port + 1, 0x1);     /* Interrupt when data received. */
        pio_write_8(port + 4, 0xB);
}

/** Disable interrupts on the serial port device.
 *
 * @param port          The base address of the serial port device's ports.
 */
static inline void ns8250_port_interrupts_disable(ioport8_t *port)
{
        pio_write_8(port + 1, 0x0);     /* Disable all interrupts. */
}

/** Enable interrupts for the serial port device.
 *
 * @param dev           The device.
 * @return              Zero on success, negative error number otherwise.
 */
static int ns8250_interrupt_enable(device_t *dev)
{
        ns8250_dev_data_t *data = (ns8250_dev_data_t *) dev->driver_data;
        
        /* Enable interrupt on the serial port. */
        ns8250_port_interrupts_enable(data->port);
        
        return EOK;
}

/** Set Divisor Latch Access Bit.
 *
 * When the Divisor Latch Access Bit is set, it is possible to set baud rate of
 * the serial port device.
 *
 * @param port          The base address of the serial port device's ports.
 */
static inline void enable_dlab(ioport8_t *port)
{
        uint8_t val = pio_read_8(port + 3);
        pio_write_8(port + 3, val | DLAB_MASK);
}

/** Clear Divisor Latch Access Bit.
 *
 * @param port          The base address of the serial port device's ports.
 */
static inline void clear_dlab(ioport8_t *port)
{
        uint8_t val = pio_read_8(port + 3);
        pio_write_8(port + 3, val & (~DLAB_MASK));
}

/** Set baud rate of the serial communication on the serial device.
 *
 * @param port          The base address of the serial port device's ports.
 * @param baud_rate     The baud rate to be used by the device.
 * @return              Zero on success, negative error number otherwise (EINVAL
 *                      if the specified baud_rate is not valid).
 */
static int ns8250_port_set_baud_rate(ioport8_t *port, unsigned int baud_rate)
{
        uint16_t divisor;
        uint8_t div_low, div_high;
        
        if (baud_rate < 50 || MAX_BAUD_RATE % baud_rate != 0) {
                printf(NAME ": error - somebody tried to set invalid baud rate "
                    "%d\n", baud_rate);
                return EINVAL;
        }
        
        divisor = MAX_BAUD_RATE / baud_rate;
        div_low = (uint8_t)divisor;
        div_high = (uint8_t)(divisor >> 8);
        
        /* Enable DLAB to be able to access baud rate divisor. */
        enable_dlab(port);
        
        /* Set divisor low byte. */
        pio_write_8(port + 0, div_low);
        /* Set divisor high byte. */
        pio_write_8(port + 1, div_high);
        
        clear_dlab(port);
        
        return EOK;
}

/** Get baud rate used by the serial port device.
 *
 * @param port          The base address of the serial port device's ports.
 * @param baud_rate     The ouput parameter to which the baud rate is stored.
 */
static unsigned int ns8250_port_get_baud_rate(ioport8_t *port)
{
        uint16_t divisor;
        uint8_t div_low, div_high;
        
        /* Enable DLAB to be able to access baud rate divisor. */
        enable_dlab(port);
        
        /* Get divisor low byte. */
        div_low = pio_read_8(port + 0);
        /* Get divisor high byte. */
        div_high = pio_read_8(port + 1);
        
        clear_dlab(port);
        
        divisor = (div_high << 8) | div_low;
        return MAX_BAUD_RATE / divisor;
}

/** Get the parameters of the serial communication set on the serial port
 * device.
 *
 * @param parity        The parity used.
 * @param word_length   The length of one data unit in bits.
 * @param stop_bits     The number of stop bits used (one or two).
 */
static void ns8250_port_get_com_props(ioport8_t *port, unsigned int *parity,
    unsigned int *word_length, unsigned int *stop_bits)
{
        uint8_t val;
        
        val = pio_read_8(port + 3);
        *parity = ((val >> 3) & 7);
        
        switch (val & 3) {
        case WORD_LENGTH_5:
                *word_length = 5;
                break;
        case WORD_LENGTH_6:
                *word_length = 6;
                break;
        case WORD_LENGTH_7:
                *word_length = 7;
                break;
        case WORD_LENGTH_8:
                *word_length = 8;
                break;
        }
        
        if ((val >> 2) & 1)
                *stop_bits = 2;
        else
                *stop_bits = 1;
}

/** Set the parameters of the serial communication on the serial port device.
 *
 * @param parity        The parity to be used.
 * @param word_length   The length of one data unit in bits.
 * @param stop_bits     The number of stop bits used (one or two).
 * @return              Zero on success, EINVAL if some of the specified values
 *                      is invalid.
 */
static int ns8250_port_set_com_props(ioport8_t *port, unsigned int parity,
    unsigned int word_length, unsigned int stop_bits)
{
        uint8_t val;
        
        switch (word_length) {
        case 5:
                val = WORD_LENGTH_5;
                break;
        case 6:
                val = WORD_LENGTH_6;
                break;
        case 7:
                val = WORD_LENGTH_7;
                break;
        case 8:
                val = WORD_LENGTH_8;
                break;
        default:
                return EINVAL;
        }
        
        switch (stop_bits) {
        case 1:
                val |= ONE_STOP_BIT << 2;
                break;
        case 2:
                val |= TWO_STOP_BITS << 2;
                break;
        default:
                return EINVAL;
        }
        
        switch (parity) {
        case SERIAL_NO_PARITY:
        case SERIAL_ODD_PARITY:
        case SERIAL_EVEN_PARITY:
        case SERIAL_MARK_PARITY:
        case SERIAL_SPACE_PARITY:
                val |= parity << 3;
                break;
        default:
                return EINVAL;
        }
        
        pio_write_8(port + 3, val);
        
        return EOK;
}

/** Initialize the serial port device.
 *
 * Set the default parameters of the serial communication.
 *
 * @param dev           The serial port device.
 */
static void ns8250_initialize_port(device_t *dev)
{
        ns8250_dev_data_t *data = (ns8250_dev_data_t *)dev->driver_data;
        ioport8_t *port = data->port;
        
        /* Disable interrupts. */
        ns8250_port_interrupts_disable(port);
        /* Set baud rate. */
        ns8250_port_set_baud_rate(port, 38400);
        /* 8 bits, no parity, two stop bits. */
        ns8250_port_set_com_props(port, SERIAL_NO_PARITY, 8, 2);
        /* Enable FIFO, clear them, with 14-byte threshold. */
        pio_write_8(port + 2, 0xC7);
        /*
         * RTS/DSR set (Request to Send and Data Terminal Ready lines enabled),
         * Aux Output2 set - needed for interrupts.
         */
        pio_write_8(port + 4, 0x0B);
}

/** Read the data from the serial port device and store them to the input
 * buffer.
 *
 * @param dev           The serial port device.
 */
static void ns8250_read_from_device(device_t *dev)
{
        ns8250_dev_data_t *data = (ns8250_dev_data_t *) dev->driver_data;
        ioport8_t *port = data->port;
        bool cont = true;
        
        while (cont) {
                fibril_mutex_lock(&data->mutex);
                
                cont = ns8250_received(port);
                if (cont) {
                        uint8_t val = ns8250_read_8(port);
                        
                        if (data->client_connected) {
                                if (!buf_push_back(&data->input_buffer, val)) {
                                        printf(NAME ": buffer overflow on "
                                            "%s.\n", dev->name);
                                } else {
                                        printf(NAME ": the character %c saved "
                                            "to the buffer of %s.\n",
                                            val, dev->name);
                                }
                        }
                }
                
                fibril_mutex_unlock(&data->mutex);
                fibril_yield();
        }
}

/** The interrupt handler.
 *
 * The serial port is initialized to interrupt when some data come, so the
 * interrupt is handled by reading the incomming data.
 *
 * @param dev           The serial port device.
 */
static inline void ns8250_interrupt_handler(device_t *dev, ipc_callid_t iid,
    ipc_call_t *icall)
{
        ns8250_read_from_device(dev);
}

/** Register the interrupt handler for the device.
 *
 * @param dev           The serial port device.
 */
static inline int ns8250_register_interrupt_handler(device_t *dev)
{
        ns8250_dev_data_t *data = (ns8250_dev_data_t *) dev->driver_data;
        
        return register_interrupt_handler(dev, data->irq,
            ns8250_interrupt_handler, NULL);
}

/** Unregister the interrupt handler for the device.
 *
 * @param dev           The serial port device.
 */
static inline int ns8250_unregister_interrupt_handler(device_t *dev)
{
        ns8250_dev_data_t *data = (ns8250_dev_data_t *) dev->driver_data;
        
        return unregister_interrupt_handler(dev, data->irq);
}

/** The add_device callback method of the serial port driver.
 *
 * Probe and initialize the newly added device.
 *
 * @param dev           The serial port device.
 */
static int ns8250_add_device(device_t *dev)
{
        printf(NAME ": ns8250_add_device %s (handle = %d)\n",
            dev->name, (int) dev->handle);
        
        int res = ns8250_dev_initialize(dev);
        if (res != EOK)
                return res;
        
        if (!ns8250_pio_enable(dev)) {
                ns8250_dev_cleanup(dev);
                return EADDRNOTAVAIL;
        }
        
        /* Find out whether the device is present. */
        if (!ns8250_dev_probe(dev)) {
                ns8250_dev_cleanup(dev);
                return ENOENT;
        }
        
        /* Serial port initialization (baud rate etc.). */
        ns8250_initialize_port(dev);
        
        /* Register interrupt handler. */
        if (ns8250_register_interrupt_handler(dev) != EOK) {
                printf(NAME ": failed to register interrupt handler.\n");
                ns8250_dev_cleanup(dev);
                return res;
        }
        
        /* Enable interrupt. */
        res = ns8250_interrupt_enable(dev);
        if (res != EOK) {
                printf(NAME ": failed to enable the interrupt. Error code = "
                    "%d.\n", res);
                ns8250_dev_cleanup(dev);
                ns8250_unregister_interrupt_handler(dev);
                return res;
        }
        
        /* Set device operations. */
        dev->ops = &ns8250_dev_ops;
        
        add_device_to_class(dev, "serial");
        
        printf(NAME ": the %s device has been successfully initialized.\n",
            dev->name);
        
        return EOK;
}

/** Open the device.
 *
 * This is a callback function called when a client tries to connect to the
 * device.
 *
 * @param dev           The device.
 */
static int ns8250_open(device_t *dev)
{
        ns8250_dev_data_t *data = (ns8250_dev_data_t *) dev->driver_data;
        int res;
        
        fibril_mutex_lock(&data->mutex);
        if (data->client_connected) {
                res = ELIMIT;
        } else {
                res = EOK;
                data->client_connected = true;
        }
        fibril_mutex_unlock(&data->mutex);

        return res;
}

/** Close the device.
 *
 * This is a callback function called when a client tries to disconnect from
 * the device.
 *
 * @param dev           The device.
 */
static void ns8250_close(device_t *dev)
{
        ns8250_dev_data_t *data = (ns8250_dev_data_t *) dev->driver_data;
        
        fibril_mutex_lock(&data->mutex);
        
        assert(data->client_connected);
        
        data->client_connected = false;
        buf_clear(&data->input_buffer);
        
        fibril_mutex_unlock(&data->mutex);
}

/** Get parameters of the serial communication which are set to the specified
 * device.
 *
 * @param dev           The serial port device.
 * @param baud_rate     The baud rate used by the device.
 * @param parity        The type of parity used by the device.
 * @param word_length   The size of one data unit in bits.
 * @param stop_bits     The number of stop bits used.
 */
static void
ns8250_get_props(device_t *dev, unsigned int *baud_rate, unsigned int *parity,
    unsigned int *word_length, unsigned int* stop_bits)
{
        ns8250_dev_data_t *data = (ns8250_dev_data_t *) dev->driver_data;
        ioport8_t *port = data->port;
        
        fibril_mutex_lock(&data->mutex);
        ns8250_port_interrupts_disable(port);
        *baud_rate = ns8250_port_get_baud_rate(port);
        ns8250_port_get_com_props(port, parity, word_length, stop_bits);
        ns8250_port_interrupts_enable(port);
        fibril_mutex_unlock(&data->mutex);
        
        printf(NAME ": ns8250_get_props: baud rate %d, parity 0x%x, word "
            "length %d, stop bits %d\n", *baud_rate, *parity, *word_length,
            *stop_bits);
}

/** Set parameters of the serial communication to the specified serial port
 * device.
 *
 * @param dev           The serial port device.
 * @param baud_rate     The baud rate to be used by the device.
 * @param parity        The type of parity to be used by the device.
 * @param word_length   The size of one data unit in bits.
 * @param stop_bits     The number of stop bits to be used.
 */
static int ns8250_set_props(device_t *dev, unsigned int baud_rate,
    unsigned int parity, unsigned int word_length, unsigned int stop_bits)
{
        printf(NAME ": ns8250_set_props: baud rate %d, parity 0x%x, word "
            "length %d, stop bits %d\n", baud_rate, parity, word_length,
            stop_bits);
        
        ns8250_dev_data_t *data = (ns8250_dev_data_t *) dev->driver_data;
        ioport8_t *port = data->port;
        int ret;
        
        fibril_mutex_lock(&data->mutex);
        ns8250_port_interrupts_disable(port);
        ret = ns8250_port_set_baud_rate(port, baud_rate);
        if (ret == EOK)
                ret = ns8250_port_set_com_props(port, parity, word_length, stop_bits);
        ns8250_port_interrupts_enable(port);
        fibril_mutex_unlock(&data->mutex);
        
        return ret;
}

/** Default handler for client requests which are not handled by the standard
 * interfaces.
 *
 * Configure the parameters of the serial communication.
 */
static void ns8250_default_handler(device_t *dev, ipc_callid_t callid,
    ipc_call_t *call)
{
        sysarg_t method = IPC_GET_IMETHOD(*call);
        int ret;
        unsigned int baud_rate, parity, word_length, stop_bits;
        
        switch (method) {
        case SERIAL_GET_COM_PROPS:
                ns8250_get_props(dev, &baud_rate, &parity, &word_length,
                    &stop_bits);
                async_answer_4(callid, EOK, baud_rate, parity, word_length,
                    stop_bits);
                break;
                
        case SERIAL_SET_COM_PROPS:
                baud_rate = IPC_GET_ARG1(*call);
                parity = IPC_GET_ARG2(*call);
                word_length = IPC_GET_ARG3(*call);
                stop_bits = IPC_GET_ARG4(*call);
                ret = ns8250_set_props(dev, baud_rate, parity, word_length,
                    stop_bits);
                async_answer_0(callid, ret);
                break;
                
        default:
                async_answer_0(callid, ENOTSUP);
        }
}

/** Initialize the serial port driver.
 *
 * Initialize device operations structures with callback methods for handling
 * client requests to the serial port devices.
 */
static void ns8250_init(void)
{
        ns8250_dev_ops.open = &ns8250_open;
        ns8250_dev_ops.close = &ns8250_close;
        
        ns8250_dev_ops.interfaces[CHAR_DEV_IFACE] = &ns8250_char_dev_ops;
        ns8250_dev_ops.default_handler = &ns8250_default_handler;
}

int main(int argc, char *argv[])
{
        printf(NAME ": HelenOS serial port driver\n");
        ns8250_init();
        return driver_main(&ns8250_driver);
}

/**
 * @}
 */