source: mainline/uspace/drv/char/ns8250/ns8250.c@ 7813516

/*
 * Copyright (c) 2010 Lenka Trochtova
 * Copyright (c) 2011 Jiri Svoboda
 * 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 <stdbool.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 <ddf/driver.h>
#include <ddf/interrupt.h>
#include <ddf/log.h>
#include <ops/char_dev.h>

#include <ns.h>
#include <ipc/services.h>
#include <ipc/irc.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)

/** Interrupt Enable Register definition. */
#define NS8250_IER_RXREADY      (1 << 0)
#define NS8250_IER_THRE         (1 << 1)
#define NS8250_IER_RXSTATUS     (1 << 2)
#define NS8250_IER_MODEM_STATUS (1 << 3)

/** Interrupt ID Register definition. */
#define NS8250_IID_ACTIVE       (1 << 0)
#define NS8250_IID_CAUSE_MASK 0x0e
#define NS8250_IID_CAUSE_RXSTATUS 0x06

/** FIFO Control Register definition. */
#define NS8250_FCR_FIFOENABLE   (1 << 0)
#define NS8250_FCR_RXFIFORESET  (1 << 1)
#define NS8250_FCR_TXFIFORESET  (1 << 2)
#define NS8250_FCR_DMAMODE      (1 << 3)
#define NS8250_FCR_RXTRIGGERLOW (1 << 6)
#define NS8250_FCR_RXTRIGGERHI  (1 << 7)

/** Line Control Register definition. */
#define NS8250_LCR_STOPBITS     (1 << 2)
#define NS8250_LCR_PARITY       (1 << 3)
#define NS8250_LCR_SENDBREAK    (1 << 6)
#define NS8250_LCR_DLAB         (1 << 7)

/** Modem Control Register definition. */
#define NS8250_MCR_DTR          (1 << 0)
#define NS8250_MCR_RTS          (1 << 1)
#define NS8250_MCR_OUT1         (1 << 2)
#define NS8250_MCR_OUT2         (1 << 3)
#define NS8250_MCR_LOOPBACK     (1 << 4)
#define NS8250_MCR_ALL          (0x1f)

/** Line Status Register definition. */
#define NS8250_LSR_RXREADY      (1 << 0)
#define NS8250_LSR_OE           (1 << 1)
#define NS8250_LSR_PE           (1 << 2)
#define NS8250_LSR_FE           (1 << 3)
#define NS8250_LSR_BREAK        (1 << 4)
#define NS8250_LSR_THRE         (1 << 5)
#define NS8250_LSR_TSE          (1 << 6)

/** Modem Status Register definition. */
#define NS8250_MSR_DELTACTS     (1 << 0)
#define NS8250_MSR_DELTADSR     (1 << 1)
#define NS8250_MSR_RITRAILING   (1 << 2)
#define NS8250_MSR_DELTADCD     (1 << 3)
#define NS8250_MSR_CTS          (1 << 4)
#define NS8250_MSR_DSR          (1 << 5)
#define NS8250_MSR_RI           (1 << 6)
#define NS8250_MSR_DCD          (1 << 7)
#define NS8250_MSR_SIGNALS      (NS8250_MSR_CTS | NS8250_MSR_DSR \
    | NS8250_MSR_RI | NS8250_MSR_DCD)

/** 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;

/** 8250 UART registers layout. */
typedef struct {
        ioport8_t data;         /**< Data register. */
        ioport8_t ier;          /**< Interrupt Enable Reg. */
        ioport8_t iid;          /**< Interrupt ID Reg. */
        ioport8_t lcr;          /**< Line Control Reg. */
        ioport8_t mcr;          /**< Modem Control Reg. */
        ioport8_t lsr;          /**< Line Status Reg. */
        ioport8_t msr;          /**< Modem Status Reg. */
} ns8250_regs_t;

/** The driver data for the serial port devices. */
typedef struct ns8250 {
        /** DDF device node */
        ddf_dev_t *dev;
        /** DDF function node */
        ddf_fun_t *fun;
        /** I/O registers **/
        ns8250_regs_t *regs;
        /** Are there any clients connected to the device? */
        unsigned client_connections;
        /** 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 incoming data. */
        cyclic_buffer_t input_buffer;
        /** The fibril mutex for synchronizing the access to the device. */
        fibril_mutex_t mutex;
        /** Indicates that some data has become available */
        fibril_condvar_t input_buffer_available;
        /** True if device is removed. */
        bool removed;
} ns8250_t;

/** Obtain soft-state structure from device node */
static ns8250_t *dev_ns8250(ddf_dev_t *dev)
{
        return ddf_dev_data_get(dev);
}

/** Obtain soft-state structure from function node */
static ns8250_t *fun_ns8250(ddf_fun_t *fun)
{
        return dev_ns8250(ddf_fun_get_dev(fun));
}

/** Find out if there is some incoming 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(ns8250_regs_t *regs)
{
        return (pio_read_8(&regs->lsr) & NS8250_LSR_RXREADY) != 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(ns8250_regs_t *regs)
{
        return pio_read_8(&regs->data);
}

/** 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(ns8250_regs_t *regs)
{
        return (pio_read_8(&regs->lsr) & NS8250_LSR_THRE) != 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(ns8250_regs_t *regs, uint8_t c)
{
        while (!is_transmit_empty(regs))
                ;
        
        pio_write_8(&regs->data, c);
}

/** Read data from the serial port device.
 *
 * @param fun           The serial port function
 * @param buf           The output 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(ddf_fun_t *fun, char *buf, size_t count)
{
        ns8250_t *ns = fun_ns8250(fun);
        int ret = 0;
        
        if (count == 0) return 0;
        
        fibril_mutex_lock(&ns->mutex);
        while (buf_is_empty(&ns->input_buffer))
                fibril_condvar_wait(&ns->input_buffer_available, &ns->mutex);
        while (!buf_is_empty(&ns->input_buffer) && (size_t)ret < count) {
                buf[ret] = (char)buf_pop_front(&ns->input_buffer);
                ret++;
        }
        fibril_mutex_unlock(&ns->mutex);
        
        return ret;
}

/** Write a character to the serial port.
 *
 * @param ns            Serial port device
 * @param c             The character to be written
 */
static inline void ns8250_putchar(ns8250_t *ns, uint8_t c)
{
        fibril_mutex_lock(&ns->mutex);
        ns8250_write_8(ns->regs, c);
        fibril_mutex_unlock(&ns->mutex);
}

/** Write data to the serial port.
 *
 * @param fun           The serial port function
 * @param buf           The data to be written
 * @param count         The number of bytes to be written
 * @return              Zero on success
 */
static int ns8250_write(ddf_fun_t *fun, char *buf, size_t count)
{
        ns8250_t *ns = fun_ns8250(fun);
        size_t idx;
        
        for (idx = 0; idx < count; idx++)
                ns8250_putchar(ns, (uint8_t) buf[idx]);
        
        return count;
}

static ddf_dev_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_dev_add(ddf_dev_t *dev);
static int ns8250_dev_remove(ddf_dev_t *dev);

/** The serial port device driver's standard operations. */
static driver_ops_t ns8250_ops = {
        .dev_add = &ns8250_dev_add,
        .dev_remove = &ns8250_dev_remove
};

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

/** Clean up the serial port soft-state
 *
 * @param ns            Serial port device
 */
static void ns8250_dev_cleanup(ns8250_t *ns)
{
}

/** Enable the i/o ports of the device.
 *
 * @param ns            Serial port device
 * @return              True on success, false otherwise
 */
static bool ns8250_pio_enable(ns8250_t *ns)
{
        ddf_msg(LVL_DEBUG, "ns8250_pio_enable %s", ddf_dev_get_name(ns->dev));
        
        /* Gain control over port's registers. */
        if (pio_enable((void *)(uintptr_t) ns->io_addr, REG_COUNT,
            (void **) &ns->port)) {
                ddf_msg(LVL_ERROR, "Cannot map the port %#" PRIx32
                    " for device %s.", ns->io_addr, ddf_dev_get_name(ns->dev));
                return false;
        }

        ns->regs = (ns8250_regs_t *)ns->port;
        
        return true;
}

/** Probe the serial port device for its presence.
 *
 * @param ns            Serial port device
 * @return              True if the device is present, false otherwise
 */
static bool ns8250_dev_probe(ns8250_t *ns)
{
        ddf_msg(LVL_DEBUG, "ns8250_dev_probe %s", ddf_dev_get_name(ns->dev));
        
        bool res = true;
        uint8_t olddata;
        
        olddata = pio_read_8(&ns->regs->mcr);
        
        pio_write_8(&ns->regs->mcr, NS8250_MCR_LOOPBACK);
        if (pio_read_8(&ns->regs->msr) & NS8250_MSR_SIGNALS)
                res = false;
        
        pio_write_8(&ns->regs->mcr, NS8250_MCR_ALL);
        if ((pio_read_8(&ns->regs->msr) & NS8250_MSR_SIGNALS) 
            != NS8250_MSR_SIGNALS)
                res = false;
        
        pio_write_8(&ns->regs->mcr, olddata);
        
        if (!res) {
                ddf_msg(LVL_DEBUG, "Device %s is not present.",
                    ddf_dev_get_name(ns->dev));
        }
        
        return res;
}

/** Initialize serial port device.
 *
 * @param ns            Serial port device
 * @return              Zero on success, negative error number otherwise
 */
static int ns8250_dev_initialize(ns8250_t *ns)
{
        async_sess_t *parent_sess;
        int ret = EOK;
        
        ddf_msg(LVL_DEBUG, "ns8250_dev_initialize %s", ddf_dev_get_name(ns->dev));
        
        hw_resource_list_t hw_resources;
        memset(&hw_resources, 0, sizeof(hw_resource_list_t));
        
        /* Connect to the parent's driver. */
        parent_sess = ddf_dev_parent_sess_create(ns->dev, EXCHANGE_SERIALIZE);
        if (parent_sess == NULL) {
                ddf_msg(LVL_ERROR, "Failed to connect to parent driver of "
                    "device %s.", ddf_dev_get_name(ns->dev));
                ret = ENOENT;
                goto failed;
        }
        
        /* Get hw resources. */
        ret = hw_res_get_resource_list(parent_sess, &hw_resources);
        if (ret != EOK) {
                ddf_msg(LVL_ERROR, "Failed to get HW resources for device "
                    "%s.", ddf_dev_get_name(ns->dev));
                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:
                        ns->irq = res->res.interrupt.irq;
                        irq = true;
                        ddf_msg(LVL_NOTE, "Device %s was assigned irq = 0x%x.",
                            ddf_dev_get_name(ns->dev), ns->irq);
                        break;
                        
                case IO_RANGE:
                        ns->io_addr = res->res.io_range.address;
                        if (res->res.io_range.size < REG_COUNT) {
                                ddf_msg(LVL_ERROR, "I/O range assigned to "
                                    "device %s is too small.", ddf_dev_get_name(ns->dev));
                                ret = ELIMIT;
                                goto failed;
                        }
                        ioport = true;
                        ddf_msg(LVL_NOTE, "Device %s was assigned I/O address = "
                            "0x%x.", ddf_dev_get_name(ns->dev), ns->io_addr);
                        break;
                        
                default:
                        break;
                }
        }
        
        if (!irq || !ioport) {
                ddf_msg(LVL_ERROR, "Missing HW resource(s) for device %s.",
                    ddf_dev_get_name(ns->dev));
                ret = ENOENT;
                goto failed;
        }
        
        hw_res_clean_resource_list(&hw_resources);
        return ret;
        
failed:
        ns8250_dev_cleanup(ns);
        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(ns8250_regs_t *regs)
{
        /* Interrupt when data received. */
        pio_write_8(&regs->ier, NS8250_IER_RXREADY | NS8250_IER_RXSTATUS);
        pio_write_8(&regs->mcr, NS8250_MCR_DTR | NS8250_MCR_RTS 
            | NS8250_MCR_OUT2);
}

/** 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(ns8250_regs_t *regs)
{
        pio_write_8(&regs->ier, 0x0);   /* Disable all interrupts. */
}

/** Enable interrupts for the serial port device.
 *
 * @param ns            Serial port device
 * @return              Zero on success, negative error number otherwise
 */
static int ns8250_interrupt_enable(ns8250_t *ns)
{
        /*
         * Enable interrupt using IRC service.
         * TODO: This is a temporary solution until the device framework
         * takes care of this itself.
         */
        async_sess_t *irc_sess = service_connect_blocking(EXCHANGE_SERIALIZE,
            SERVICE_IRC, 0, 0);
        if (!irc_sess) {
                return EIO;
        }

        async_exch_t *exch = async_exchange_begin(irc_sess);
        if (!exch) {
                return EIO;
        }
        async_msg_1(exch, IRC_ENABLE_INTERRUPT, ns->irq);
        async_exchange_end(exch);

        /* Read LSR to clear possible previous LSR interrupt */
        pio_read_8(&ns->regs->lsr);

        /* Enable interrupt on the serial port. */
        ns8250_port_interrupts_enable(ns->regs);
        
        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(ns8250_regs_t *regs)
{
        uint8_t val = pio_read_8(&regs->lcr);
        pio_write_8(&regs->lcr, val | NS8250_LCR_DLAB);
}

/** Clear Divisor Latch Access Bit.
 *
 * @param port          The base address of the serial port device's ports.
 */
static inline void clear_dlab(ns8250_regs_t *regs)
{
        uint8_t val = pio_read_8(&regs->lcr);
        pio_write_8(&regs->lcr, val & (~NS8250_LCR_DLAB));
}

/** 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(ns8250_regs_t *regs, unsigned int baud_rate)
{
        uint16_t divisor;
        uint8_t div_low, div_high;
        
        if (baud_rate < 50 || MAX_BAUD_RATE % baud_rate != 0) {
                ddf_msg(LVL_ERROR, "Invalid baud rate %d requested.",
                    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(regs);
        
        /* Set divisor low byte. */
        pio_write_8(&regs->data, div_low);
        /* Set divisor high byte. */
        pio_write_8(&regs->ier, div_high);
        
        clear_dlab(regs);
        
        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(ns8250_regs_t *regs)
{
        uint16_t divisor;
        uint8_t div_low, div_high;
        
        /* Enable DLAB to be able to access baud rate divisor. */
        enable_dlab(regs);
        
        /* Get divisor low byte. */
        div_low = pio_read_8(&regs->data);
        /* Get divisor high byte. */
        div_high = pio_read_8(&regs->ier);
        
        clear_dlab(regs);
        
        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(ns8250_regs_t *regs, unsigned int *parity,
    unsigned int *word_length, unsigned int *stop_bits)
{
        uint8_t val;
        
        val = pio_read_8(&regs->lcr);
        *parity = ((val >> NS8250_LCR_PARITY) & 7);
        
        /* Silence warnings */
        *word_length = 0;

        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 >> NS8250_LCR_STOPBITS) & 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(ns8250_regs_t *regs, 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 << NS8250_LCR_STOPBITS;
                break;
        case 2:
                val |= TWO_STOP_BITS << NS8250_LCR_STOPBITS;
                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 << NS8250_LCR_PARITY;
                break;
        default:
                return EINVAL;
        }
        
        pio_write_8(&regs->lcr, val);
        
        return EOK;
}

/** Initialize the serial port device.
 *
 * Set the default parameters of the serial communication.
 *
 * @param ns            Serial port device
 */
static void ns8250_initialize_port(ns8250_t *ns)
{
        /* Disable interrupts. */
        ns8250_port_interrupts_disable(ns->regs);
        /* Set baud rate. */
        ns8250_port_set_baud_rate(ns->regs, 38400);
        /* 8 bits, no parity, two stop bits. */
        ns8250_port_set_com_props(ns->regs, SERIAL_NO_PARITY, 8, 2);
        /*
         * Enable FIFO, clear them, with 4-byte threshold for greater
         * reliability.
         */
        pio_write_8(&ns->regs->iid, NS8250_FCR_FIFOENABLE
            | NS8250_FCR_RXFIFORESET | NS8250_FCR_TXFIFORESET
            | NS8250_FCR_RXTRIGGERLOW);
        /*
         * RTS/DSR set (Request to Send and Data Terminal Ready lines enabled),
         * Aux Output2 set - needed for interrupts.
         */
        pio_write_8(&ns->regs->mcr, NS8250_MCR_DTR | NS8250_MCR_RTS
            | NS8250_MCR_OUT2);
}

/** Deinitialize the serial port device.
 *
 * @param ns            Serial port device
 */
static void ns8250_port_cleanup(ns8250_t *ns)
{
        /* Disable FIFO */
        pio_write_8(&ns->regs->iid, 0x00);
        /* Disable DTR, RTS, OUT1, OUT2 (int. enable) */
        pio_write_8(&ns->regs->mcr, 0x00);
        /* Disable all interrupts from the port */
        ns8250_port_interrupts_disable(ns->regs);
}

/** Read the data from the serial port device and store them to the input
 * buffer.
 *
 * @param ns            Serial port device
 */
static void ns8250_read_from_device(ns8250_t *ns)
{
        ns8250_regs_t *regs = ns->regs;
        bool cont = true;
        
        fibril_mutex_lock(&ns->mutex);
        while (cont) {
                cont = ns8250_received(regs);
                if (cont) {
                        uint8_t val = ns8250_read_8(regs);
                        
                        if (ns->client_connections > 0) {
                                bool buf_was_empty = buf_is_empty(&ns->input_buffer);
                                if (!buf_push_back(&ns->input_buffer, val)) {
                                        ddf_msg(LVL_WARN, "Buffer overflow on "
                                            "%s.", ddf_dev_get_name(ns->dev));
                                        break;
                                } else {
                                        ddf_msg(LVL_DEBUG2, "Character %c saved "
                                            "to the buffer of %s.",
                                            val, ddf_dev_get_name(ns->dev));
                                        if (buf_was_empty)
                                                fibril_condvar_broadcast(&ns->input_buffer_available);
                                }
                        }
                }
        }
        fibril_mutex_unlock(&ns->mutex);
        fibril_yield();
}

/** The interrupt handler.
 *
 * The serial port is initialized to interrupt when some data come or line
 * status register changes, so the interrupt is handled by reading the incoming
 * data and reading the line status register.
 *
 * @param dev           The serial port device.
 */
static inline void ns8250_interrupt_handler(ddf_dev_t *dev, ipc_callid_t iid,
    ipc_call_t *icall)
{
        ns8250_t *ns = dev_ns8250(dev);

        uint8_t iir = pio_read_8(&ns->regs->iid);
        if ((iir & NS8250_IID_CAUSE_MASK) == NS8250_IID_CAUSE_RXSTATUS) {
                uint8_t lsr = pio_read_8(&ns->regs->lsr);
                if (lsr & NS8250_LSR_OE) {
                        ddf_msg(LVL_WARN, "Overrun error on %s", ddf_dev_get_name(ns->dev));
                }
        }
        
        ns8250_read_from_device(ns);
}

/** Register the interrupt handler for the device.
 *
 * @param ns            Serial port device
 */
static inline int ns8250_register_interrupt_handler(ns8250_t *ns)
{
        return register_interrupt_handler(ns->dev, ns->irq,
            ns8250_interrupt_handler, NULL);
}

/** Unregister the interrupt handler for the device.
 *
 * @param ns            Serial port device
 */
static inline int ns8250_unregister_interrupt_handler(ns8250_t *ns)
{
        return unregister_interrupt_handler(ns->dev, ns->irq);
}

/** The dev_add callback method of the serial port driver.
 *
 * Probe and initialize the newly added device.
 *
 * @param dev           The serial port device.
 */
static int ns8250_dev_add(ddf_dev_t *dev)
{
        ns8250_t *ns = NULL;
        ddf_fun_t *fun = NULL;
        bool need_cleanup = false;
        bool need_unreg_intr_handler = false;
        int rc;
        
        ddf_msg(LVL_DEBUG, "ns8250_dev_add %s (handle = %d)",
            ddf_dev_get_name(dev), (int) ddf_dev_get_handle(dev));
        
        /* Allocate soft-state for the device */
        ns = ddf_dev_data_alloc(dev, sizeof(ns8250_t));
        if (ns == NULL) {
                rc = ENOMEM;
                goto fail;
        }
        
        fibril_mutex_initialize(&ns->mutex);
        fibril_condvar_initialize(&ns->input_buffer_available);
        ns->dev = dev;
        
        rc = ns8250_dev_initialize(ns);
        if (rc != EOK)
                goto fail;
        
        need_cleanup = true;
        
        if (!ns8250_pio_enable(ns)) {
                rc = EADDRNOTAVAIL;
                goto fail;
        }
        
        /* Find out whether the device is present. */
        if (!ns8250_dev_probe(ns)) {
                rc = ENOENT;
                goto fail;
        }
        
        /* Serial port initialization (baud rate etc.). */
        ns8250_initialize_port(ns);
        
        /* Register interrupt handler. */
        if (ns8250_register_interrupt_handler(ns) != EOK) {
                ddf_msg(LVL_ERROR, "Failed to register interrupt handler.");
                rc = EADDRNOTAVAIL;
                goto fail;
        }
        need_unreg_intr_handler = true;
        
        /* Enable interrupt. */
        rc = ns8250_interrupt_enable(ns);
        if (rc != EOK) {
                ddf_msg(LVL_ERROR, "Failed to enable the interrupt. Error code = "
                    "%d.", rc);
                goto fail;
        }
        
        fun = ddf_fun_create(dev, fun_exposed, "a");
        if (fun == NULL) {
                ddf_msg(LVL_ERROR, "Failed creating function.");
                goto fail;
        }
        
        /* Set device operations. */
        ddf_fun_set_ops(fun, &ns8250_dev_ops);
        rc = ddf_fun_bind(fun);
        if (rc != EOK) {
                ddf_msg(LVL_ERROR, "Failed binding function.");
                goto fail;
        }

        ns->fun = fun;
        
        ddf_fun_add_to_category(fun, "serial");
        
        ddf_msg(LVL_NOTE, "Device %s successfully initialized.",
            ddf_dev_get_name(dev));
        
        return EOK;
fail:
        if (fun != NULL)
                ddf_fun_destroy(fun);
        if (need_unreg_intr_handler)
                ns8250_unregister_interrupt_handler(ns);
        if (need_cleanup)
                ns8250_dev_cleanup(ns);
        return rc;
}

static int ns8250_dev_remove(ddf_dev_t *dev)
{
        ns8250_t *ns = dev_ns8250(dev);
        int rc;
        
        fibril_mutex_lock(&ns->mutex);
        if (ns->client_connections > 0) {
                fibril_mutex_unlock(&ns->mutex);
                return EBUSY;
        }
        ns->removed = true;
        fibril_mutex_unlock(&ns->mutex);
        
        rc = ddf_fun_unbind(ns->fun);
        if (rc != EOK) {
                ddf_msg(LVL_ERROR, "Failed to unbind function.");
                return rc;
        }
        
        ddf_fun_destroy(ns->fun);
        
        ns8250_port_cleanup(ns);
        ns8250_unregister_interrupt_handler(ns);
        ns8250_dev_cleanup(ns);
        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(ddf_fun_t *fun)
{
        ns8250_t *ns = fun_ns8250(fun);
        int res;
        
        fibril_mutex_lock(&ns->mutex);
        if (ns->removed) {
                res = ENXIO;
        } else {
                res = EOK;
                ns->client_connections++;
        }
        fibril_mutex_unlock(&ns->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(ddf_fun_t *fun)
{
        ns8250_t *data = fun_ns8250(fun);
        
        fibril_mutex_lock(&data->mutex);
        
        assert(data->client_connections > 0);
        
        if (!(--data->client_connections))
                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(ddf_dev_t *dev, unsigned int *baud_rate, unsigned int *parity,
    unsigned int *word_length, unsigned int* stop_bits)
{
        ns8250_t *data = dev_ns8250(dev);
        ns8250_regs_t *regs = data->regs;
        
        fibril_mutex_lock(&data->mutex);
        ns8250_port_interrupts_disable(regs);
        *baud_rate = ns8250_port_get_baud_rate(regs);
        ns8250_port_get_com_props(regs, parity, word_length, stop_bits);
        ns8250_port_interrupts_enable(regs);
        fibril_mutex_unlock(&data->mutex);
        
        ddf_msg(LVL_DEBUG, "ns8250_get_props: baud rate %d, parity 0x%x, word "
            "length %d, stop bits %d", *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(ddf_dev_t *dev, unsigned int baud_rate,
    unsigned int parity, unsigned int word_length, unsigned int stop_bits)
{
        ddf_msg(LVL_DEBUG, "ns8250_set_props: baud rate %d, parity 0x%x, word "
            "length %d, stop bits %d", baud_rate, parity, word_length,
            stop_bits);
        
        ns8250_t *data = dev_ns8250(dev);
        ns8250_regs_t *regs = data->regs;
        int ret;
        
        fibril_mutex_lock(&data->mutex);
        ns8250_port_interrupts_disable(regs);
        ret = ns8250_port_set_baud_rate(regs, baud_rate);
        if (ret == EOK)
                ret = ns8250_port_set_com_props(regs, parity, word_length, stop_bits);
        ns8250_port_interrupts_enable(regs);
        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(ddf_fun_t *fun, 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(ddf_fun_get_dev(fun), &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(ddf_fun_get_dev(fun), 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)
{
        ddf_log_init(NAME);
        
        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 ddf_driver_main(&ns8250_driver);
}

/**
 * @}
 */