jsm_tty.c

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/************************************************************************
 * Copyright 2003 Digi International (www.digi.com)
 *
 * Copyright (C) 2004 IBM Corporation. All rights reserved.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2, or (at your option)
 * any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY, EXPRESS OR IMPLIED; without even the
 * implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
 * PURPOSE.  See the GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 * Temple Place - Suite 330, Boston,
 * MA  02111-1307, USA.
 *
 * Contact Information:
 * Scott H Kilau <[email protected]>
 * Ananda Venkatarman <[email protected]>
 * Modifications:
 * 01/19/06:    changed jsm_input routine to use the dynamically allocated
 *      tty_buffer changes. Contributors: Scott Kilau and Ananda V.
 ***********************************************************************/
#include <linux/tty.h>
#include <linux/tty_flip.h>
#include <linux/serial_reg.h>
#include <linux/delay.h>    /* For udelay */
#include <linux/pci.h>
#include <linux/slab.h>

#include "jsm.h"

static DECLARE_BITMAP(linemap, MAXLINES);

static void jsm_carrier(struct jsm_channel *ch);

static inline int jsm_get_mstat(struct jsm_channel *ch)
{
    unsigned char mstat;
    unsigned result;

    jsm_printk(IOCTL, INFO, &ch->ch_bd->pci_dev, "start\n");

    mstat = (ch->ch_mostat | ch->ch_mistat);

    result = 0;

    if (mstat & UART_MCR_DTR)
        result |= TIOCM_DTR;
    if (mstat & UART_MCR_RTS)
        result |= TIOCM_RTS;
    if (mstat & UART_MSR_CTS)
        result |= TIOCM_CTS;
    if (mstat & UART_MSR_DSR)
        result |= TIOCM_DSR;
    if (mstat & UART_MSR_RI)
        result |= TIOCM_RI;
    if (mstat & UART_MSR_DCD)
        result |= TIOCM_CD;

    jsm_printk(IOCTL, INFO, &ch->ch_bd->pci_dev, "finish\n");
    return result;
}

static unsigned int jsm_tty_tx_empty(struct uart_port *port)
{
    return TIOCSER_TEMT;
}

/*
 * Return modem signals to ld.
 */
static unsigned int jsm_tty_get_mctrl(struct uart_port *port)
{
    int result;
    struct jsm_channel *channel = (struct jsm_channel *)port;

    jsm_printk(IOCTL, INFO, &channel->ch_bd->pci_dev, "start\n");

    result = jsm_get_mstat(channel);

    if (result < 0)
        return -ENXIO;

    jsm_printk(IOCTL, INFO, &channel->ch_bd->pci_dev, "finish\n");

    return result;
}

/*
 * jsm_set_modem_info()
 *
 * Set modem signals, called by ld.
 */
static void jsm_tty_set_mctrl(struct uart_port *port, unsigned int mctrl)
{
    struct jsm_channel *channel = (struct jsm_channel *)port;

    jsm_printk(IOCTL, INFO, &channel->ch_bd->pci_dev, "start\n");

    if (mctrl & TIOCM_RTS)
        channel->ch_mostat |= UART_MCR_RTS;
    else
        channel->ch_mostat &= ~UART_MCR_RTS;

    if (mctrl & TIOCM_DTR)
        channel->ch_mostat |= UART_MCR_DTR;
    else
        channel->ch_mostat &= ~UART_MCR_DTR;

    channel->ch_bd->bd_ops->assert_modem_signals(channel);

    jsm_printk(IOCTL, INFO, &channel->ch_bd->pci_dev, "finish\n");
    udelay(10);
}

/*
 * jsm_tty_write()
 *
 * Take data from the user or kernel and send it out to the FEP.
 * In here exists all the Transparent Print magic as well.
 */
static void jsm_tty_write(struct uart_port *port)
{
    struct jsm_channel *channel;
    channel = container_of(port, struct jsm_channel, uart_port);
    channel->ch_bd->bd_ops->copy_data_from_queue_to_uart(channel);
}

static void jsm_tty_start_tx(struct uart_port *port)
{
    struct jsm_channel *channel = (struct jsm_channel *)port;

    jsm_printk(IOCTL, INFO, &channel->ch_bd->pci_dev, "start\n");

    channel->ch_flags &= ~(CH_STOP);
    jsm_tty_write(port);

    jsm_printk(IOCTL, INFO, &channel->ch_bd->pci_dev, "finish\n");
}

static void jsm_tty_stop_tx(struct uart_port *port)
{
    struct jsm_channel *channel = (struct jsm_channel *)port;

    jsm_printk(IOCTL, INFO, &channel->ch_bd->pci_dev, "start\n");

    channel->ch_flags |= (CH_STOP);

    jsm_printk(IOCTL, INFO, &channel->ch_bd->pci_dev, "finish\n");
}

static void jsm_tty_send_xchar(struct uart_port *port, char ch)
{
    unsigned long lock_flags;
    struct jsm_channel *channel = (struct jsm_channel *)port;
    struct ktermios *termios;

    spin_lock_irqsave(&port->lock, lock_flags);
    termios = &port->state->port.tty->termios;
    if (ch == termios->c_cc[VSTART])
        channel->ch_bd->bd_ops->send_start_character(channel);

    if (ch == termios->c_cc[VSTOP])
        channel->ch_bd->bd_ops->send_stop_character(channel);
    spin_unlock_irqrestore(&port->lock, lock_flags);
}

static void jsm_tty_stop_rx(struct uart_port *port)
{
    struct jsm_channel *channel = (struct jsm_channel *)port;

    channel->ch_bd->bd_ops->disable_receiver(channel);
}

static void jsm_tty_enable_ms(struct uart_port *port)
{
    /* Nothing needed */
}

static void jsm_tty_break(struct uart_port *port, int break_state)
{
    unsigned long lock_flags;
    struct jsm_channel *channel = (struct jsm_channel *)port;

    spin_lock_irqsave(&port->lock, lock_flags);
    if (break_state == -1)
        channel->ch_bd->bd_ops->send_break(channel);
    else
        channel->ch_bd->bd_ops->clear_break(channel, 0);

    spin_unlock_irqrestore(&port->lock, lock_flags);
}

static int jsm_tty_open(struct uart_port *port)
{
    struct jsm_board *brd;
    struct jsm_channel *channel = (struct jsm_channel *)port;
    struct ktermios *termios;

    /* Get board pointer from our array of majors we have allocated */
    brd = channel->ch_bd;

    /*
     * Allocate channel buffers for read/write/error.
     * Set flag, so we don't get trounced on.
     */
    channel->ch_flags |= (CH_OPENING);

    /* Drop locks, as malloc with GFP_KERNEL can sleep */

    if (!channel->ch_rqueue) {
        channel->ch_rqueue = kzalloc(RQUEUESIZE, GFP_KERNEL);
        if (!channel->ch_rqueue) {
            jsm_printk(INIT, ERR, &channel->ch_bd->pci_dev,
                "unable to allocate read queue buf");
            return -ENOMEM;
        }
    }
    if (!channel->ch_equeue) {
        channel->ch_equeue = kzalloc(EQUEUESIZE, GFP_KERNEL);
        if (!channel->ch_equeue) {
            jsm_printk(INIT, ERR, &channel->ch_bd->pci_dev,
                "unable to allocate error queue buf");
            return -ENOMEM;
        }
    }

    channel->ch_flags &= ~(CH_OPENING);
    /*
     * Initialize if neither terminal is open.
     */
    jsm_printk(OPEN, INFO, &channel->ch_bd->pci_dev,
        "jsm_open: initializing channel in open...\n");

    /*
     * Flush input queues.
     */
    channel->ch_r_head = channel->ch_r_tail = 0;
    channel->ch_e_head = channel->ch_e_tail = 0;

    brd->bd_ops->flush_uart_write(channel);
    brd->bd_ops->flush_uart_read(channel);

    channel->ch_flags = 0;
    channel->ch_cached_lsr = 0;
    channel->ch_stops_sent = 0;

    termios = &port->state->port.tty->termios;
    channel->ch_c_cflag = termios->c_cflag;
    channel->ch_c_iflag = termios->c_iflag;
    channel->ch_c_oflag = termios->c_oflag;
    channel->ch_c_lflag = termios->c_lflag;
    channel->ch_startc  = termios->c_cc[VSTART];
    channel->ch_stopc   = termios->c_cc[VSTOP];

    /* Tell UART to init itself */
    brd->bd_ops->uart_init(channel);

    /*
     * Run param in case we changed anything
     */
    brd->bd_ops->param(channel);

    jsm_carrier(channel);

    channel->ch_open_count++;

    jsm_printk(OPEN, INFO, &channel->ch_bd->pci_dev, "finish\n");
    return 0;
}

static void jsm_tty_close(struct uart_port *port)
{
    struct jsm_board *bd;
    struct ktermios *ts;
    struct jsm_channel *channel = (struct jsm_channel *)port;

    jsm_printk(CLOSE, INFO, &channel->ch_bd->pci_dev, "start\n");

    bd = channel->ch_bd;
    ts = &port->state->port.tty->termios;

    channel->ch_flags &= ~(CH_STOPI);

    channel->ch_open_count--;

    /*
     * If we have HUPCL set, lower DTR and RTS
     */
    if (channel->ch_c_cflag & HUPCL) {
        jsm_printk(CLOSE, INFO, &channel->ch_bd->pci_dev,
            "Close. HUPCL set, dropping DTR/RTS\n");

        /* Drop RTS/DTR */
        channel->ch_mostat &= ~(UART_MCR_DTR | UART_MCR_RTS);
        bd->bd_ops->assert_modem_signals(channel);
    }

    /* Turn off UART interrupts for this port */
    channel->ch_bd->bd_ops->uart_off(channel);

    jsm_printk(CLOSE, INFO, &channel->ch_bd->pci_dev, "finish\n");
}

static void jsm_tty_set_termios(struct uart_port *port,
                 struct ktermios *termios,
                 struct ktermios *old_termios)
{
    unsigned long lock_flags;
    struct jsm_channel *channel = (struct jsm_channel *)port;

    spin_lock_irqsave(&port->lock, lock_flags);
    channel->ch_c_cflag = termios->c_cflag;
    channel->ch_c_iflag = termios->c_iflag;
    channel->ch_c_oflag = termios->c_oflag;
    channel->ch_c_lflag = termios->c_lflag;
    channel->ch_startc  = termios->c_cc[VSTART];
    channel->ch_stopc   = termios->c_cc[VSTOP];

    channel->ch_bd->bd_ops->param(channel);
    jsm_carrier(channel);
    spin_unlock_irqrestore(&port->lock, lock_flags);
}

static const char *jsm_tty_type(struct uart_port *port)
{
    return "jsm";
}

static void jsm_tty_release_port(struct uart_port *port)
{
}

static int jsm_tty_request_port(struct uart_port *port)
{
    return 0;
}

static void jsm_config_port(struct uart_port *port, int flags)
{
    port->type = PORT_JSM;
}

static struct uart_ops jsm_ops = {
    .tx_empty   = jsm_tty_tx_empty,
    .set_mctrl  = jsm_tty_set_mctrl,
    .get_mctrl  = jsm_tty_get_mctrl,
    .stop_tx    = jsm_tty_stop_tx,
    .start_tx   = jsm_tty_start_tx,
    .send_xchar = jsm_tty_send_xchar,
    .stop_rx    = jsm_tty_stop_rx,
    .enable_ms  = jsm_tty_enable_ms,
    .break_ctl  = jsm_tty_break,
    .startup    = jsm_tty_open,
    .shutdown   = jsm_tty_close,
    .set_termios    = jsm_tty_set_termios,
    .type       = jsm_tty_type,
    .release_port   = jsm_tty_release_port,
    .request_port   = jsm_tty_request_port,
    .config_port    = jsm_config_port,
};

/*
 * jsm_tty_init()
 *
 * Init the tty subsystem.  Called once per board after board has been
 * downloaded and init'ed.
 */
int __devinit jsm_tty_init(struct jsm_board *brd)
{
    int i;
    void __iomem *vaddr;
    struct jsm_channel *ch;

    if (!brd)
        return -ENXIO;

    jsm_printk(INIT, INFO, &brd->pci_dev, "start\n");

    /*
     * Initialize board structure elements.
     */

    brd->nasync = brd->maxports;

    /*
     * Allocate channel memory that might not have been allocated
     * when the driver was first loaded.
     */
    for (i = 0; i < brd->nasync; i++) {
        if (!brd->channels[i]) {

            /*
             * Okay to malloc with GFP_KERNEL, we are not at
             * interrupt context, and there are no locks held.
             */
            brd->channels[i] = kzalloc(sizeof(struct jsm_channel), GFP_KERNEL);
            if (!brd->channels[i]) {
                jsm_printk(CORE, ERR, &brd->pci_dev,
                    "%s:%d Unable to allocate memory for channel struct\n",
                             __FILE__, __LINE__);
            }
        }
    }

    ch = brd->channels[0];
    vaddr = brd->re_map_membase;

    /* Set up channel variables */
    for (i = 0; i < brd->nasync; i++, ch = brd->channels[i]) {

        if (!brd->channels[i])
            continue;

        spin_lock_init(&ch->ch_lock);

        if (brd->bd_uart_offset == 0x200)
            ch->ch_neo_uart =  vaddr + (brd->bd_uart_offset * i);

        ch->ch_bd = brd;
        ch->ch_portnum = i;

        /* .25 second delay */
        ch->ch_close_delay = 250;

        init_waitqueue_head(&ch->ch_flags_wait);
    }

    jsm_printk(INIT, INFO, &brd->pci_dev, "finish\n");
    return 0;
}

int jsm_uart_port_init(struct jsm_board *brd)
{
    int i, rc;
    unsigned int line;
    struct jsm_channel *ch;

    if (!brd)
        return -ENXIO;

    jsm_printk(INIT, INFO, &brd->pci_dev, "start\n");

    /*
     * Initialize board structure elements.
     */

    brd->nasync = brd->maxports;

    /* Set up channel variables */
    for (i = 0; i < brd->nasync; i++, ch = brd->channels[i]) {

        if (!brd->channels[i])
            continue;

        brd->channels[i]->uart_port.irq = brd->irq;
        brd->channels[i]->uart_port.uartclk = 14745600;
        brd->channels[i]->uart_port.type = PORT_JSM;
        brd->channels[i]->uart_port.iotype = UPIO_MEM;
        brd->channels[i]->uart_port.membase = brd->re_map_membase;
        brd->channels[i]->uart_port.fifosize = 16;
        brd->channels[i]->uart_port.ops = &jsm_ops;
        line = find_first_zero_bit(linemap, MAXLINES);
        if (line >= MAXLINES) {
            printk(KERN_INFO "jsm: linemap is full, added device failed\n");
            continue;
        } else
            set_bit(line, linemap);
        brd->channels[i]->uart_port.line = line;
        rc = uart_add_one_port (&jsm_uart_driver, &brd->channels[i]->uart_port);
        if (rc){
            printk(KERN_INFO "jsm: Port %d failed. Aborting...\n", i);
            return rc;
        }
        else
            printk(KERN_INFO "jsm: Port %d added\n", i);
    }

    jsm_printk(INIT, INFO, &brd->pci_dev, "finish\n");
    return 0;
}

int jsm_remove_uart_port(struct jsm_board *brd)
{
    int i;
    struct jsm_channel *ch;

    if (!brd)
        return -ENXIO;

    jsm_printk(INIT, INFO, &brd->pci_dev, "start\n");

    /*
     * Initialize board structure elements.
     */

    brd->nasync = brd->maxports;

    /* Set up channel variables */
    for (i = 0; i < brd->nasync; i++) {

        if (!brd->channels[i])
            continue;

        ch = brd->channels[i];

        clear_bit(ch->uart_port.line, linemap);
        uart_remove_one_port(&jsm_uart_driver, &brd->channels[i]->uart_port);
    }

    jsm_printk(INIT, INFO, &brd->pci_dev, "finish\n");
    return 0;
}

void jsm_input(struct jsm_channel *ch)
{
    struct jsm_board *bd;
    struct tty_struct *tp;
    u32 rmask;
    u16 head;
    u16 tail;
    int data_len;
    unsigned long lock_flags;
    int len = 0;
    int n = 0;
    int s = 0;
    int i = 0;

    jsm_printk(READ, INFO, &ch->ch_bd->pci_dev, "start\n");

    if (!ch)
        return;

    tp = ch->uart_port.state->port.tty;

    bd = ch->ch_bd;
    if(!bd)
        return;

    spin_lock_irqsave(&ch->ch_lock, lock_flags);

    /*
     *Figure the number of characters in the buffer.
     *Exit immediately if none.
     */

    rmask = RQUEUEMASK;

    head = ch->ch_r_head & rmask;
    tail = ch->ch_r_tail & rmask;

    data_len = (head - tail) & rmask;
    if (data_len == 0) {
        spin_unlock_irqrestore(&ch->ch_lock, lock_flags);
        return;
    }

    jsm_printk(READ, INFO, &ch->ch_bd->pci_dev, "start\n");

    /*
     *If the device is not open, or CREAD is off, flush
     *input data and return immediately.
     */
    if (!tp ||
        !(tp->termios.c_cflag & CREAD) ) {

        jsm_printk(READ, INFO, &ch->ch_bd->pci_dev,
            "input. dropping %d bytes on port %d...\n", data_len, ch->ch_portnum);
        ch->ch_r_head = tail;

        /* Force queue flow control to be released, if needed */
        jsm_check_queue_flow_control(ch);

        spin_unlock_irqrestore(&ch->ch_lock, lock_flags);
        return;
    }

    /*
     * If we are throttled, simply don't read any data.
     */
    if (ch->ch_flags & CH_STOPI) {
        spin_unlock_irqrestore(&ch->ch_lock, lock_flags);
        jsm_printk(READ, INFO, &ch->ch_bd->pci_dev,
            "Port %d throttled, not reading any data. head: %x tail: %x\n",
            ch->ch_portnum, head, tail);
        return;
    }

    jsm_printk(READ, INFO, &ch->ch_bd->pci_dev, "start 2\n");

    if (data_len <= 0) {
        spin_unlock_irqrestore(&ch->ch_lock, lock_flags);
        jsm_printk(READ, INFO, &ch->ch_bd->pci_dev, "jsm_input 1\n");
        return;
    }

    len = tty_buffer_request_room(tp, data_len);
    n = len;

    /*
     * n now contains the most amount of data we can copy,
     * bounded either by the flip buffer size or the amount
     * of data the card actually has pending...
     */
    while (n) {
        s = ((head >= tail) ? head : RQUEUESIZE) - tail;
        s = min(s, n);

        if (s <= 0)
            break;

            /*
             * If conditions are such that ld needs to see all
             * UART errors, we will have to walk each character
             * and error byte and send them to the buffer one at
             * a time.
             */

        if (I_PARMRK(tp) || I_BRKINT(tp) || I_INPCK(tp)) {
            for (i = 0; i < s; i++) {
                /*
                 * Give the Linux ld the flags in the
                 * format it likes.
                 */
                if (*(ch->ch_equeue +tail +i) & UART_LSR_BI)
                    tty_insert_flip_char(tp, *(ch->ch_rqueue +tail +i),  TTY_BREAK);
                else if (*(ch->ch_equeue +tail +i) & UART_LSR_PE)
                    tty_insert_flip_char(tp, *(ch->ch_rqueue +tail +i), TTY_PARITY);
                else if (*(ch->ch_equeue +tail +i) & UART_LSR_FE)
                    tty_insert_flip_char(tp, *(ch->ch_rqueue +tail +i), TTY_FRAME);
                else
                    tty_insert_flip_char(tp, *(ch->ch_rqueue +tail +i), TTY_NORMAL);
            }
        } else {
            tty_insert_flip_string(tp, ch->ch_rqueue + tail, s) ;
        }
        tail += s;
        n -= s;
        /* Flip queue if needed */
        tail &= rmask;
    }

    ch->ch_r_tail = tail & rmask;
    ch->ch_e_tail = tail & rmask;
    jsm_check_queue_flow_control(ch);
    spin_unlock_irqrestore(&ch->ch_lock, lock_flags);

    /* Tell the tty layer its okay to "eat" the data now */
    tty_flip_buffer_push(tp);

    jsm_printk(IOCTL, INFO, &ch->ch_bd->pci_dev, "finish\n");
}

static void jsm_carrier(struct jsm_channel *ch)
{
    struct jsm_board *bd;

    int virt_carrier = 0;
    int phys_carrier = 0;

    jsm_printk(CARR, INFO, &ch->ch_bd->pci_dev, "start\n");
    if (!ch)
        return;

    bd = ch->ch_bd;

    if (!bd)
        return;

    if (ch->ch_mistat & UART_MSR_DCD) {
        jsm_printk(CARR, INFO, &ch->ch_bd->pci_dev,
            "mistat: %x D_CD: %x\n", ch->ch_mistat, ch->ch_mistat & UART_MSR_DCD);
        phys_carrier = 1;
    }

    if (ch->ch_c_cflag & CLOCAL)
        virt_carrier = 1;

    jsm_printk(CARR, INFO, &ch->ch_bd->pci_dev,
        "DCD: physical: %d virt: %d\n", phys_carrier, virt_carrier);

    /*
     * Test for a VIRTUAL carrier transition to HIGH.
     */
    if (((ch->ch_flags & CH_FCAR) == 0) && (virt_carrier == 1)) {

        /*
         * When carrier rises, wake any threads waiting
         * for carrier in the open routine.
         */

        jsm_printk(CARR, INFO, &ch->ch_bd->pci_dev,
            "carrier: virt DCD rose\n");

        if (waitqueue_active(&(ch->ch_flags_wait)))
            wake_up_interruptible(&ch->ch_flags_wait);
    }

    /*
     * Test for a PHYSICAL carrier transition to HIGH.
     */
    if (((ch->ch_flags & CH_CD) == 0) && (phys_carrier == 1)) {

        /*
         * When carrier rises, wake any threads waiting
         * for carrier in the open routine.
         */

        jsm_printk(CARR, INFO, &ch->ch_bd->pci_dev,
            "carrier: physical DCD rose\n");

        if (waitqueue_active(&(ch->ch_flags_wait)))
            wake_up_interruptible(&ch->ch_flags_wait);
    }

    /*
     *  Test for a PHYSICAL transition to low, so long as we aren't
     *  currently ignoring physical transitions (which is what "virtual
     *  carrier" indicates).
     *
     *  The transition of the virtual carrier to low really doesn't
     *  matter... it really only means "ignore carrier state", not
     *  "make pretend that carrier is there".
     */
    if ((virt_carrier == 0) && ((ch->ch_flags & CH_CD) != 0)
            && (phys_carrier == 0)) {
        /*
         *  When carrier drops:
         *
         *  Drop carrier on all open units.
         *
         *  Flush queues, waking up any task waiting in the
         *  line discipline.
         *
         *  Send a hangup to the control terminal.
         *
         *  Enable all select calls.
         */
        if (waitqueue_active(&(ch->ch_flags_wait)))
            wake_up_interruptible(&ch->ch_flags_wait);
    }

    /*
     *  Make sure that our cached values reflect the current reality.
     */
    if (virt_carrier == 1)
        ch->ch_flags |= CH_FCAR;
    else
        ch->ch_flags &= ~CH_FCAR;

    if (phys_carrier == 1)
        ch->ch_flags |= CH_CD;
    else
        ch->ch_flags &= ~CH_CD;
}


void jsm_check_queue_flow_control(struct jsm_channel *ch)
{
    struct board_ops *bd_ops = ch->ch_bd->bd_ops;
    int qleft;

    /* Store how much space we have left in the queue */
    if ((qleft = ch->ch_r_tail - ch->ch_r_head - 1) < 0)
        qleft += RQUEUEMASK + 1;

    /*
     * Check to see if we should enforce flow control on our queue because
     * the ld (or user) isn't reading data out of our queue fast enuf.
     *
     * NOTE: This is done based on what the current flow control of the
     * port is set for.
     *
     * 1) HWFLOW (RTS) - Turn off the UART's Receive interrupt.
     *  This will cause the UART's FIFO to back up, and force
     *  the RTS signal to be dropped.
     * 2) SWFLOW (IXOFF) - Keep trying to send a stop character to
     *  the other side, in hopes it will stop sending data to us.
     * 3) NONE - Nothing we can do.  We will simply drop any extra data
     *  that gets sent into us when the queue fills up.
     */
    if (qleft < 256) {
        /* HWFLOW */
        if (ch->ch_c_cflag & CRTSCTS) {
            if(!(ch->ch_flags & CH_RECEIVER_OFF)) {
                bd_ops->disable_receiver(ch);
                ch->ch_flags |= (CH_RECEIVER_OFF);
                jsm_printk(READ, INFO, &ch->ch_bd->pci_dev,
                    "Internal queue hit hilevel mark (%d)! Turning off interrupts.\n",
                    qleft);
            }
        }
        /* SWFLOW */
        else if (ch->ch_c_iflag & IXOFF) {
            if (ch->ch_stops_sent <= MAX_STOPS_SENT) {
                bd_ops->send_stop_character(ch);
                ch->ch_stops_sent++;
                jsm_printk(READ, INFO, &ch->ch_bd->pci_dev,
                    "Sending stop char! Times sent: %x\n", ch->ch_stops_sent);
            }
        }
    }

    /*
     * Check to see if we should unenforce flow control because
     * ld (or user) finally read enuf data out of our queue.
     *
     * NOTE: This is done based on what the current flow control of the
     * port is set for.
     *
     * 1) HWFLOW (RTS) - Turn back on the UART's Receive interrupt.
     *  This will cause the UART's FIFO to raise RTS back up,
     *  which will allow the other side to start sending data again.
     * 2) SWFLOW (IXOFF) - Send a start character to
     *  the other side, so it will start sending data to us again.
     * 3) NONE - Do nothing. Since we didn't do anything to turn off the
     *  other side, we don't need to do anything now.
     */
    if (qleft > (RQUEUESIZE / 2)) {
        /* HWFLOW */
        if (ch->ch_c_cflag & CRTSCTS) {
            if (ch->ch_flags & CH_RECEIVER_OFF) {
                bd_ops->enable_receiver(ch);
                ch->ch_flags &= ~(CH_RECEIVER_OFF);
                jsm_printk(READ, INFO, &ch->ch_bd->pci_dev,
                    "Internal queue hit lowlevel mark (%d)! Turning on interrupts.\n",
                    qleft);
            }
        }
        /* SWFLOW */
        else if (ch->ch_c_iflag & IXOFF && ch->ch_stops_sent) {
            ch->ch_stops_sent = 0;
            bd_ops->send_start_character(ch);
            jsm_printk(READ, INFO, &ch->ch_bd->pci_dev, "Sending start char!\n");
        }
    }
}