source: mainline/uspace/drv/char/ns8250/ns8250.c@ f08da1c

/*
 * Copyright (c) 2010 Lenka Trochtova
 * Copyright (c) 2017 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.
 */

/**
 * @addtogroup ns8250
 * @{
 */

/** @file
 */

#include <assert.h>
#include <stdio.h>
#include <errno.h>
#include <str_error.h>
#include <stdbool.h>
#include <fibril_synch.h>
#include <stdlib.h>
#include <str.h>
#include <ctype.h>
#include <macros.h>
#include <stdlib.h>
#include <dirent.h>
#include <ddi.h>

#include <ddf/driver.h>
#include <ddf/interrupt.h>
#include <ddf/log.h>
#include <io/chardev_srv.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;
        /** Character device service */
        chardev_srvs_t cds;
        /** Parent session */
        async_sess_t *parent_sess;
        /** 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;
        /** IRQ capability handle */
        cap_irq_handle_t irq_handle;
        /** The base i/o address of the devices registers. */
        uintptr_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));
}

/** Obtain soft-state structure from chardev srv */
static ns8250_t *srv_ns8250(chardev_srv_t *srv)
{
        return (ns8250_t *)srv->srvs->sarg;
}

/** 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 srv           Server-side connection data
 * @param buf           The output buffer for read data.
 * @param count         The number of bytes to be read.
 * @param nread         Place to store number of bytes actually read
 * @param flags         @c chardev_f_nonblock not to block waiting for data
 *                      even if no data is available
 *
 * @return              EOK on success or non-zero error code
 */
static errno_t ns8250_read(chardev_srv_t *srv, void *buf, size_t count, size_t *nread,
    chardev_flags_t flags)
{
        ns8250_t *ns = srv_ns8250(srv);
        char *bp = (char *) buf;
        size_t pos = 0;

        if (count == 0) {
                *nread = 0;
                return EOK;
        }

        fibril_mutex_lock(&ns->mutex);
        while ((flags & chardev_f_none) == 0 &&
            buf_is_empty(&ns->input_buffer))
                fibril_condvar_wait(&ns->input_buffer_available, &ns->mutex);
        while (!buf_is_empty(&ns->input_buffer) && pos < count) {
                bp[pos] = (char)buf_pop_front(&ns->input_buffer);
                pos++;
        }
        fibril_mutex_unlock(&ns->mutex);

        *nread = pos;
        return EOK;
}

/** 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 srv           Server-side connection data
 * @param buf           The data to be written
 * @param count         The number of bytes to be written
 * @param nwritten      Place to store number of bytes successfully written
 * @return              EOK on success or non-zero error code
 */
static errno_t ns8250_write(chardev_srv_t *srv, const void *buf, size_t count,
    size_t *nwritten)
{
        ns8250_t *ns = srv_ns8250(srv);
        size_t idx;
        uint8_t *bp = (uint8_t *) buf;

        for (idx = 0; idx < count; idx++)
                ns8250_putchar(ns, bp[idx]);

        *nwritten = count;
        return EOK;
}

static errno_t ns8250_open(chardev_srvs_t *, chardev_srv_t *);
static errno_t ns8250_close(chardev_srv_t *);
static void ns8250_default_handler(chardev_srv_t *, ipc_call_t *);

/** The character interface's callbacks. */
static chardev_ops_t ns8250_chardev_ops = {
        .open = ns8250_open,
        .close = ns8250_close,
        .read = ns8250_read,
        .write = ns8250_write,
        .def_handler = ns8250_default_handler
};

static void ns8250_char_conn(ipc_call_t *, void *);

static errno_t ns8250_dev_add(ddf_dev_t *dev);
static errno_t 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 *) ns->io_addr, REG_COUNT,
            (void **) &ns->port)) {
                ddf_msg(LVL_ERROR, "Cannot map the port %#" PRIxn
                    " 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, error number otherwise
 */
static errno_t ns8250_dev_initialize(ns8250_t *ns)
{
        errno_t 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));

        /* Get hw resources. */
        ret = hw_res_get_resource_list(ns->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%#" PRIxn ".", 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, error number otherwise
 */
static errno_t ns8250_interrupt_enable(ns8250_t *ns)
{
        /* Enable interrupt using IRC service. */
        errno_t rc = hw_res_enable_interrupt(ns->parent_sess, ns->irq);
        if (rc != EOK)
                return EIO;

        /* 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, error number otherwise (EINVAL
 *                      if the specified baud_rate is not valid).
 */
static errno_t 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 errno_t 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(ipc_call_t *icall, ddf_dev_t *dev)
{
        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);
        hw_res_clear_interrupt(ns->parent_sess, ns->irq);
}

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

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

/** The dev_add callback method of the serial port driver.
 *
 * Probe and initialize the newly added device.
 *
 * @param dev           The serial port device.
 */
static errno_t 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;
        bool bound = false;
        errno_t 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;

        ns->parent_sess = ddf_dev_parent_sess_get(ns->dev);
        if (ns->parent_sess == NULL) {
                ddf_msg(LVL_ERROR, "Failed to connect to parent driver of "
                    "device %s.", ddf_dev_get_name(ns->dev));
                rc = EIO;
                goto fail;
        }

        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. */
        ns->irq_handle = CAP_NIL;
        rc = ns8250_register_interrupt_handler(ns, &ns->irq_handle);
        if (rc != 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 = "
                    "%s.", str_error_name(rc));
                goto fail;
        }

        fun = ddf_fun_create(dev, fun_exposed, "a");
        if (fun == NULL) {
                ddf_msg(LVL_ERROR, "Failed creating function.");
                goto fail;
        }

        ddf_fun_set_conn_handler(fun, ns8250_char_conn);

        chardev_srvs_init(&ns->cds);
        ns->cds.ops = &ns8250_chardev_ops;
        ns->cds.sarg = ns;

        rc = ddf_fun_bind(fun);
        if (rc != EOK) {
                ddf_msg(LVL_ERROR, "Failed binding function.");
                goto fail;
        }

        bound = true;
        ns->fun = fun;

        rc = ddf_fun_add_to_category(fun, "serial");
        if (rc != EOK) {
                ddf_msg(LVL_ERROR, "Error adding function to category 'serial'.");
                goto fail;
        }

        ddf_msg(LVL_NOTE, "Device %s successfully initialized.",
            ddf_dev_get_name(dev));

        return EOK;
fail:
        if (bound)
                ddf_fun_unbind(fun);
        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 errno_t ns8250_dev_remove(ddf_dev_t *dev)
{
        ns8250_t *ns = dev_ns8250(dev);
        errno_t 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 srvs          Service structure
 * @param srv           Server-side connection structure
 */
static errno_t ns8250_open(chardev_srvs_t *srvs, chardev_srv_t *srv)
{
        ns8250_t *ns = srv_ns8250(srv);
        errno_t 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 srv           Server-side connection structure
 */
static errno_t ns8250_close(chardev_srv_t *srv)
{
        ns8250_t *data = srv_ns8250(srv);

        fibril_mutex_lock(&data->mutex);

        assert(data->client_connections > 0);

        if (!(--data->client_connections))
                buf_clear(&data->input_buffer);

        fibril_mutex_unlock(&data->mutex);

        return EOK;
}

/** 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 errno_t 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;
        errno_t 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(chardev_srv_t *srv, ipc_call_t *call)
{
        ns8250_t *ns8250 = srv_ns8250(srv);
        sysarg_t method = IPC_GET_IMETHOD(*call);
        errno_t ret;
        unsigned int baud_rate, parity, word_length, stop_bits;

        switch (method) {
        case SERIAL_GET_COM_PROPS:
                ns8250_get_props(ns8250->dev, &baud_rate, &parity, &word_length,
                    &stop_bits);
                async_answer_4(call, 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(ns8250->dev, baud_rate, parity, word_length,
                    stop_bits);
                async_answer_0(call, ret);
                break;

        default:
                async_answer_0(call, ENOTSUP);
        }
}

void ns8250_char_conn(ipc_call_t *icall, void *arg)
{
        ns8250_t *ns8250 = fun_ns8250((ddf_fun_t *)arg);

        chardev_conn(icall, &ns8250->cds);
}

/** 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);
}

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

/**
 * @}
 */