/*      $OpenBSD: z8530tty.c,v 1.32 2020/01/09 14:35:19 mpi Exp $       */
/*      $NetBSD: z8530tty.c,v 1.77 2001/05/30 15:24:24 lukem Exp $      */

/*-
 * Copyright (c) 1993, 1994, 1995, 1996, 1997, 1998, 1999
 *      Charles M. Hannum.  All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. 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.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *      This product includes software developed by Charles M. Hannum.
 * 4. 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.
 */

/*
 * Copyright (c) 1994 Gordon W. Ross
 * Copyright (c) 1992, 1993
 *      The Regents of the University of California.  All rights reserved.
 *
 * This software was developed by the Computer Systems Engineering group
 * at Lawrence Berkeley Laboratory under DARPA contract BG 91-66 and
 * contributed to Berkeley.
 *
 * All advertising materials mentioning features or use of this software
 * must display the following acknowledgement:
 *      This product includes software developed by the University of
 *      California, Lawrence Berkeley Laboratory.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. 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.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``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 REGENTS OR CONTRIBUTORS 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.
 *
 *      @(#)zs.c        8.1 (Berkeley) 7/19/93
 */

/*
 * Zilog Z8530 Dual UART driver (tty interface)
 *
 * This is the "slave" driver that will be attached to
 * the "zsc" driver for plain "tty" async. serial lines.
 *
 * Credits, history:
 *
 * The original version of this code was the sparc/dev/zs.c driver
 * as distributed with the Berkeley 4.4 Lite release.  Since then,
 * Gordon Ross reorganized the code into the current parent/child
 * driver scheme, separating the Sun keyboard and mouse support
 * into independent child drivers.
 *
 * RTS/CTS flow-control support was a collaboration of:
 *      Gordon Ross <gwr@NetBSD.org>,
 *      Bill Studenmund <wrstuden@loki.stanford.edu>
 *      Ian Dall <Ian.Dall@dsto.defence.gov.au>
 *
 * The driver was massively overhauled in November 1997 by Charles Hannum,
 * fixing *many* bugs, and substantially improving performance.
 */

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/proc.h>
#include <sys/device.h>
#include <sys/conf.h>
#include <sys/fcntl.h>
#include <sys/ioctl.h>
#include <sys/malloc.h>
#include <sys/tty.h>
#include <sys/time.h>
#include <sys/kernel.h>
#include <sys/syslog.h>

#include <dev/ic/z8530reg.h>
#include <machine/z8530var.h>

#include <dev/cons.h>

/*
 * Allow the MD var.h to override the default CFLAG so that
 * console messages during boot come out with correct parity.
 */
#ifndef ZSTTY_DEF_CFLAG
#define ZSTTY_DEF_CFLAG TTYDEF_CFLAG
#endif

/*
 * How many input characters we can buffer.
 * The port-specific var.h may override this.
 * Note: must be a power of two!
 */
#ifndef ZSTTY_RING_SIZE
#define ZSTTY_RING_SIZE 2048
#endif

struct cfdriver zstty_cd = {
        NULL, "zstty", DV_TTY
};

/*
 * Make this an option variable one can patch.
 * But be warned:  this must be a power of 2!
 */
u_int zstty_rbuf_size = ZSTTY_RING_SIZE;

/* Stop input when 3/4 of the ring is full; restart when only 1/4 is full. */
u_int zstty_rbuf_hiwat = (ZSTTY_RING_SIZE * 1) / 4;
u_int zstty_rbuf_lowat = (ZSTTY_RING_SIZE * 3) / 4;

struct zstty_softc {
        struct  device zst_dev;         /* required first: base device */
        struct  tty *zst_tty;
        struct  zs_chanstate *zst_cs;

        struct timeout zst_diag_ch;

        u_int zst_overflows,
              zst_floods,
              zst_errors;

        int zst_hwflags,        /* see z8530var.h */
            zst_swflags;        /* TIOCFLAG_SOFTCAR, ... <ttycom.h> */

        u_int zst_r_hiwat,
              zst_r_lowat;
        uint8_t *volatile zst_rbget,
                *volatile zst_rbput;
        volatile u_int zst_rbavail;
        uint8_t *zst_rbuf,
                *zst_ebuf;

        /*
         * The transmit byte count and address are used for pseudo-DMA
         * output in the hardware interrupt code.  PDMA can be suspended
         * to get pending changes done; heldtbc is used for this.  It can
         * also be stopped for ^S; this sets TS_TTSTOP in tp->t_state.
         */
        uint8_t *zst_tba;               /* transmit buffer address */
        u_int zst_tbc,                  /* transmit byte count */
              zst_heldtbc;              /* held tbc while xmission stopped */

        /* Flags to communicate with zstty_softint() */
        volatile uint8_t zst_rx_flags,  /* receiver blocked */
#define RX_TTY_BLOCKED          0x01
#define RX_TTY_OVERFLOWED       0x02
#define RX_IBUF_BLOCKED         0x04
#define RX_IBUF_OVERFLOWED      0x08
#define RX_ANY_BLOCK            0x0f
                        zst_tx_busy,    /* working on an output chunk */
                        zst_tx_done,    /* done with one output chunk */
                        zst_tx_stopped, /* H/W level stop (lost CTS) */
                        zst_st_check,   /* got a status interrupt */
                        zst_rx_ready;

        /* PPS signal on DCD, with or without inkernel clock disciplining */
        uint8_t  zst_ppsmask;                   /* pps signal mask */
        uint8_t  zst_ppsassert;                 /* pps leading edge */
        uint8_t  zst_ppsclear;                  /* pps trailing edge */
};

/* Definition of the driver for autoconfig. */
int     zstty_match(struct device *, void *, void *);
void    zstty_attach(struct device *, struct device *, void *);

const struct cfattach zstty_ca = {
        sizeof(struct zstty_softc), zstty_match, zstty_attach
};

cdev_decl(zs);

struct zsops zsops_tty;

void zs_shutdown(struct zstty_softc *);
void    zsstart(struct tty *);
int     zsparam(struct tty *, struct termios *);
void zs_modem(struct zstty_softc *, int);
void tiocm_to_zs(struct zstty_softc *, u_long, int);
int  zs_to_tiocm(struct zstty_softc *);
int    zshwiflow(struct tty *, int);
void  zs_hwiflow(struct zstty_softc *);
void zs_maskintr(struct zstty_softc *);

struct zstty_softc *zs_device_lookup(struct cfdriver *, int);

/* Low-level routines. */
void zstty_rxint(struct zs_chanstate *);
void zstty_stint(struct zs_chanstate *, int);
void zstty_txint(struct zs_chanstate *);
void zstty_softint(struct zs_chanstate *);
void zstty_diag(void *);

#define ZSUNIT(x)       (minor(x) & 0x7f)
#define ZSDIALOUT(x)    (minor(x) & 0x80)

struct zstty_softc *
zs_device_lookup(struct cfdriver *cf, int unit)
{
        return (struct zstty_softc *)device_lookup(cf, unit);
}

/*
 * zstty_match: how is this zs channel configured?
 */
int
zstty_match(struct device *parent, void *vcf, void *aux)
{
        struct cfdata *cf = vcf;
        struct zsc_attach_args *args = aux;

        /* Exact match is better than wildcard. */
        if (cf->cf_loc[0] == args->channel)
                return 2;

        /* This driver accepts wildcard. */
        if (cf->cf_loc[0] == -1)
                return 1;

        return 0;
}

void
zstty_attach(struct device *parent, struct device *self, void *aux)
{
        struct zsc_softc *zsc = (struct zsc_softc *)parent;
        struct zstty_softc *zst = (struct zstty_softc *)self;
        struct cfdata *cf = self->dv_cfdata;
        struct zsc_attach_args *args = aux;
        struct zs_chanstate *cs;
        struct tty *tp;
        int channel, s, tty_unit;
        dev_t dev;
        const char *i, *o;
        int dtr_on;
        int resetbit;

        timeout_set(&zst->zst_diag_ch, zstty_diag, zst);

        tty_unit = zst->zst_dev.dv_unit;
        channel = args->channel;
        cs = zsc->zsc_cs[channel];
        cs->cs_private = zst;
        cs->cs_ops = &zsops_tty;

        zst->zst_cs = cs;
        zst->zst_swflags = cf->cf_flags;        /* softcar, etc. */
        zst->zst_hwflags = args->hwflags;
        dev = makedev(zs_major, tty_unit);

        if (zst->zst_swflags)
                printf(" flags 0x%x", zst->zst_swflags);

        if (ISSET(zst->zst_hwflags, ZS_HWFLAG_NO_DCD))
                SET(zst->zst_swflags, TIOCFLAG_SOFTCAR);

        /*
         * Check whether we serve as a console device.
         * XXX - split console input/output channels aren't
         *       supported yet on /dev/console
         */
        i = o = NULL;
        if ((zst->zst_hwflags & ZS_HWFLAG_CONSOLE_INPUT) != 0) {
                i = " input";
                if ((args->hwflags & ZS_HWFLAG_USE_CONSDEV) != 0) {
                        args->consdev->cn_dev = dev;
                        cn_tab->cn_pollc = args->consdev->cn_pollc;
                        cn_tab->cn_getc = args->consdev->cn_getc;
                }
                cn_tab->cn_dev = dev;
        }
        if ((zst->zst_hwflags & ZS_HWFLAG_CONSOLE_OUTPUT) != 0) {
                o = " output";
                if ((args->hwflags & ZS_HWFLAG_USE_CONSDEV) != 0) {
                        cn_tab->cn_putc = args->consdev->cn_putc;
                }
                cn_tab->cn_dev = dev;
        }
        if (i != NULL || o != NULL) {
                printf(": console%s", i ? (o ? "" : i) : o);
        }

#if defined(__sparc64__)
        if (strcmp(args->type, "keyboard") == 0 ||
            strcmp(args->type, "mouse") == 0)
                printf(": %s", args->type);
#endif

        printf("\n");

        tp = ttymalloc(0);
        tp->t_dev = dev;
        tp->t_oproc = zsstart;
        tp->t_param = zsparam;
        tp->t_hwiflow = zshwiflow;

        zst->zst_tty = tp;
        zst->zst_rbuf = mallocarray(zstty_rbuf_size, 2, M_DEVBUF, M_WAITOK);
        zst->zst_ebuf = zst->zst_rbuf + (zstty_rbuf_size * 2);
        /* Disable the high water mark. */
        zst->zst_r_hiwat = 0;
        zst->zst_r_lowat = 0;
        zst->zst_rbget = zst->zst_rbput = zst->zst_rbuf;
        zst->zst_rbavail = zstty_rbuf_size;

        /* if there are no enable/disable functions, assume the device
           is always enabled */
        if (!cs->enable)
                cs->enabled = 1;

        /*
         * Hardware init
         */
        dtr_on = 0;
        resetbit = 0;
        if (ISSET(zst->zst_hwflags, ZS_HWFLAG_CONSOLE)) {
                /* Call zsparam similar to open. */
                struct termios t;

                /* Wait a while for previous console output to complete */
                DELAY(10000);

                /* Setup the "new" parameters in t. */
                t.c_ispeed = 0;
                t.c_ospeed = cs->cs_defspeed;
                t.c_cflag = cs->cs_defcflag;

                s = splzs();

                /*
                 * Turn on receiver and status interrupts.
                 * We defer the actual write of the register to zsparam(),
                 * but we must make sure status interrupts are turned on by
                 * the time zsparam() reads the initial rr0 state.
                 */
                SET(cs->cs_preg[1], ZSWR1_RIE | ZSWR1_TIE | ZSWR1_SIE);

                splx(s);

                /* Make sure zsparam will see changes. */
                tp->t_ospeed = 0;
                (void)zsparam(tp, &t);

                /* Make sure DTR is on now. */
                dtr_on = 1;
        } else if (!ISSET(zst->zst_hwflags, ZS_HWFLAG_NORESET)) {
                /* Not the console; may need reset. */
                resetbit = (channel == 0) ? ZSWR9_A_RESET : ZSWR9_B_RESET;
        }

        s = splzs();
        if (resetbit)
                zs_write_reg(cs, 9, resetbit);
        zs_modem(zst, dtr_on);
        splx(s);
}


/*
 * Return pointer to our tty.
 */
struct tty *
zstty(dev_t dev)
{
        struct zstty_softc *zst = zs_device_lookup(&zstty_cd, ZSUNIT(dev));

        return (zst->zst_tty);
}


void
zs_shutdown(struct zstty_softc *zst)
{
        struct zs_chanstate *cs = zst->zst_cs;
        struct tty *tp = zst->zst_tty;
        int s;

        s = splzs();

        /* If we were asserting flow control, then deassert it. */
        SET(zst->zst_rx_flags, RX_IBUF_BLOCKED);
        zs_hwiflow(zst);

        /* Clear any break condition set with TIOCSBRK. */
        zs_break(cs, 0);

        /* Turn off PPS capture on last close. */
        zst->zst_ppsmask = 0;

        /*
         * Hang up if necessary.  Wait a bit, so the other side has time to
         * notice even if we immediately open the port again.
         */
        if (ISSET(tp->t_cflag, HUPCL) || ISSET(tp->t_state, TS_WOPEN)) {
                zs_modem(zst, 0);
                /* hold low for 1 second */
                tsleep_nsec(cs, TTIPRI, ttclos, SEC_TO_NSEC(1));
        }

        /* Turn off interrupts if not the console. */
        if (!ISSET(zst->zst_hwflags, ZS_HWFLAG_CONSOLE)) {
                CLR(cs->cs_preg[1], ZSWR1_RIE | ZSWR1_TIE | ZSWR1_SIE);
                cs->cs_creg[1] = cs->cs_preg[1];
                zs_write_reg(cs, 1, cs->cs_creg[1]);
        }

        /* Call the power management hook. */
        if (cs->disable) {
#ifdef DIAGNOSTIC
                if (!cs->enabled)
                        panic("%s: not enabled?", __func__);
#endif
                (*cs->disable)(zst->zst_cs);
        }

        splx(s);
}

/*
 * Open a zs serial (tty) port.
 */
int
zsopen(dev_t dev, int flags, int mode, struct proc *p)
{
        struct zstty_softc *zst;
        struct zs_chanstate *cs;
        struct tty *tp;
        int s;
#if IPL_ZS != IPL_TTY
        int s2;
#endif
        int error;

        zst = zs_device_lookup(&zstty_cd, ZSUNIT(dev));
        if (zst == NULL)
                return (ENXIO);

        tp = zst->zst_tty;
        cs = zst->zst_cs;

        /* If KGDB took the line, then tp==NULL */
        if (tp == NULL)
                return (EBUSY);

        if (ISSET(tp->t_state, TS_ISOPEN) &&
            ISSET(tp->t_state, TS_XCLUDE) &&
            suser(p) != 0)
                return (EBUSY);

        s = spltty();

        /*
         * Do the following iff this is a first open.
         */
        if (!ISSET(tp->t_state, TS_ISOPEN)) {
                struct termios t;

                tp->t_dev = dev;

                /* Call the power management hook. */
                if (cs->enable) {
                        if ((*cs->enable)(cs)) {
                                splx(s);
                                printf("%s: device enable failed\n",
                                    zst->zst_dev.dv_xname);
                                return (EIO);
                        }
                }

                /*
                 * Initialize the termios status to the defaults.  Add in the
                 * sticky bits from TIOCSFLAGS.
                 */
                t.c_ispeed = 0;
                t.c_ospeed = cs->cs_defspeed;
                t.c_cflag = cs->cs_defcflag;
                if (ISSET(zst->zst_swflags, TIOCFLAG_CLOCAL))
                        SET(t.c_cflag, CLOCAL);
                if (ISSET(zst->zst_swflags, TIOCFLAG_CRTSCTS))
                        SET(t.c_cflag, CRTSCTS);
                if (ISSET(zst->zst_swflags, TIOCFLAG_MDMBUF))
                        SET(t.c_cflag, MDMBUF);

#if IPL_ZS != IPL_TTY
                s2 = splzs();
#endif

                /*
                 * Turn on receiver and status interrupts.
                 * We defer the actual write of the register to zsparam(),
                 * but we must make sure status interrupts are turned on by
                 * the time zsparam() reads the initial rr0 state.
                 */
                SET(cs->cs_preg[1], ZSWR1_RIE | ZSWR1_TIE | ZSWR1_SIE);

                /* Clear PPS capture state on first open. */
                zst->zst_ppsmask = 0;

#if IPL_ZS != IPL_TTY
                splx(s2);
#endif

                /* Make sure zsparam will see changes. */
                tp->t_ospeed = 0;
                (void)zsparam(tp, &t);

                /*
                 * Note: zsparam has done: cflag, ispeed, ospeed
                 * so we just need to do: iflag, oflag, lflag, cc
                 * For "raw" mode, just leave all zeros.
                 */
                if (!ISSET(zst->zst_hwflags, ZS_HWFLAG_RAW)) {
                        tp->t_iflag = TTYDEF_IFLAG;
                        tp->t_oflag = TTYDEF_OFLAG;
                        tp->t_lflag = TTYDEF_LFLAG;
                } else {
                        tp->t_iflag = 0;
                        tp->t_oflag = 0;
                        tp->t_lflag = 0;
                }
                ttychars(tp);
                ttsetwater(tp);

                if (ZSDIALOUT(dev))
                        SET(tp->t_state, TS_CARR_ON);
                else
                        CLR(tp->t_state, TS_CARR_ON);

#if IPL_ZS != IPL_TTY
                s2 = splzs();
#endif

                /* Clear the input ring, and unblock. */
                zst->zst_rbget = zst->zst_rbput = zst->zst_rbuf;
                zst->zst_rbavail = zstty_rbuf_size;
                zs_iflush(cs);
                CLR(zst->zst_rx_flags, RX_ANY_BLOCK);
                zs_hwiflow(zst);

#if IPL_ZS != IPL_TTY
                splx(s2);
#endif
        }

        if (ZSDIALOUT(dev)) {
                if (ISSET(tp->t_state, TS_ISOPEN)) {
                        /* someone already is dialed in... */
                        splx(s);
                        return EBUSY;
                }
                cs->cs_cua = 1;
        }

        error = 0;
        /* wait for carrier if necessary */
        if (ISSET(flags, O_NONBLOCK)) {
                if (!ZSDIALOUT(dev) && cs->cs_cua) {
                        /* Opening TTY non-blocking... but the CUA is busy */
                        error = EBUSY;
                }
        } else
          while (cs->cs_cua ||
            (!ISSET(tp->t_cflag, CLOCAL) && !ISSET(tp->t_state, TS_CARR_ON))) {
                int rr0;

                error = 0;
                SET(tp->t_state, TS_WOPEN);

                if (!ZSDIALOUT(dev) && !cs->cs_cua) {
                        /*
                         * Turn on DTR.  We must always do this on non-CUA
                         * devices, even if carrier is not present, because
                         * otherwise we'd have to use TIOCSDTR immediately
                         * after setting CLOCAL, which applications do not
                         * expect.  We always assert DTR while the device is
                         * open unless explicitly requested to deassert it.
                         */
#if IPL_ZS != IPL_TTY
                        s2 = splzs();
#endif
                        zs_modem(zst, 1);
                        rr0 = zs_read_csr(cs);
#if IPL_ZS != IPL_TTY
                        splx(s2);
#endif

                        /* loop, turning on the device, until carrier present */
                        if (ISSET(rr0, ZSRR0_DCD) ||
                            ISSET(zst->zst_swflags, TIOCFLAG_SOFTCAR))
                                SET(tp->t_state, TS_CARR_ON);
                }

                if ((ISSET(tp->t_cflag, CLOCAL) ||
                    ISSET(tp->t_state, TS_CARR_ON)) && !cs->cs_cua)
                        break;

                error = ttysleep(tp, (caddr_t)&tp->t_rawq, TTIPRI | PCATCH,
                    ttopen);

                if (!ZSDIALOUT(dev) && cs->cs_cua && error == EINTR) {
                        error = 0;
                        continue;
                }

                if (error) {
                        if (!ISSET(tp->t_state, TS_ISOPEN)) {
#if IPL_ZS != IPL_TTY
                                s2 = splzs();
#endif
                                zs_modem(zst, 0);
#if IPL_ZS != IPL_TTY
                                splx(s2);
#endif
                                CLR(tp->t_state, TS_WOPEN);
                                ttwakeup(tp);
                        }
                        if (ZSDIALOUT(dev))
                                cs->cs_cua = 0;
                        CLR(tp->t_state, TS_WOPEN);
                        break;
                }
                if (!ZSDIALOUT(dev) && cs->cs_cua)
                        continue;
        }

        splx(s);

        if (error == 0)
                error = ((*linesw[tp->t_line].l_open)(dev, tp, p));
        if (error)
                goto bad;

        return (0);

bad:
        if (!ISSET(tp->t_state, TS_ISOPEN)) {
                /*
                 * We failed to open the device, and nobody else had it opened.
                 * Clean up the state as appropriate.
                 */
                zs_shutdown(zst);
        }

        return (error);
}

/*
 * Close a zs serial port.
 */
int
zsclose(dev_t dev, int flags, int mode, struct proc *p)
{
        struct zstty_softc *zst = zs_device_lookup(&zstty_cd, ZSUNIT(dev));
        struct zs_chanstate *cs = zst->zst_cs;
        struct tty *tp = zst->zst_tty;
        int s;

        /* XXX This is for cons.c. */
        if (!ISSET(tp->t_state, TS_ISOPEN))
                return 0;

        (*linesw[tp->t_line].l_close)(tp, flags, p);

        s = spltty();
        cs->cs_cua = 0;
        ttyclose(tp);
        splx(s);

        if (!ISSET(tp->t_state, TS_ISOPEN)) {
                /*
                 * Although we got a last close, the device may still be in
                 * use; e.g. if this was the dialout node, and there are still
                 * processes waiting for carrier on the non-dialout node.
                 */
                zs_shutdown(zst);
        }

        return (0);
}

/*
 * Read/write zs serial port.
 */
int
zsread(dev_t dev, struct uio *uio, int flags)
{
        struct zstty_softc *zst = zs_device_lookup(&zstty_cd, ZSUNIT(dev));
        struct tty *tp = zst->zst_tty;

        return (*linesw[tp->t_line].l_read)(tp, uio, flags);
}

int
zswrite(dev_t dev, struct uio *uio, int flags)
{
        struct zstty_softc *zst = zs_device_lookup(&zstty_cd, ZSUNIT(dev));
        struct tty *tp = zst->zst_tty;

        return (*linesw[tp->t_line].l_write)(tp, uio, flags);
}

int
zsioctl(dev_t dev, u_long cmd, caddr_t data, int flag, struct proc *p)
{
        struct zstty_softc *zst = zs_device_lookup(&zstty_cd, ZSUNIT(dev));
        struct zs_chanstate *cs = zst->zst_cs;
        struct tty *tp = zst->zst_tty;
        int error;
        int s;

        error = (*linesw[tp->t_line].l_ioctl)(tp, cmd, data, flag, p);
        if (error >= 0)
                return (error);

        error = ttioctl(tp, cmd, data, flag, p);
        if (error >= 0)
                return (error);

#ifdef  ZS_MD_IOCTL
        error = ZS_MD_IOCTL;
        if (error >= 0)
                return (error);
#endif  /* ZS_MD_IOCTL */

        error = 0;

        s = splzs();

        switch (cmd) {
        case TIOCSBRK:
                zs_break(cs, 1);
                break;

        case TIOCCBRK:
                zs_break(cs, 0);
                break;

        case TIOCGFLAGS:
                *(int *)data = zst->zst_swflags;
                break;

        case TIOCSFLAGS:
                error = suser(p);
                if (error)
                        break;
                zst->zst_swflags = *(int *)data;
                if (ISSET(zst->zst_hwflags, ZS_HWFLAG_NO_DCD))
                        SET(zst->zst_swflags, TIOCFLAG_SOFTCAR);
                break;

        case TIOCSDTR:
                zs_modem(zst, 1);
                break;

        case TIOCCDTR:
                zs_modem(zst, 0);
                break;

        case TIOCMSET:
        case TIOCMBIS:
        case TIOCMBIC:
                tiocm_to_zs(zst, cmd, *(int *)data);
                break;

        case TIOCMGET:
                *(int *)data = zs_to_tiocm(zst);
                break;

        default:
                error = ENOTTY;
                break;
        }

        splx(s);

        return (error);
}

/*
 * Start or restart transmission.
 */
void
zsstart(struct tty *tp)
{
        struct zstty_softc *zst = zs_device_lookup(&zstty_cd, ZSUNIT(tp->t_dev));
        struct zs_chanstate *cs = zst->zst_cs;
        u_char *tba;
        int tbc, rr0;
        int s;

        s = spltty();
        if (ISSET(tp->t_state, TS_BUSY | TS_TIMEOUT | TS_TTSTOP))
                goto out;
        if (zst->zst_tx_stopped)
                goto out;

        ttwakeupwr(tp);
        if (tp->t_outq.c_cc == 0)
                goto out;

        /* Grab the first contiguous region of buffer space. */
        tba = tp->t_outq.c_cf;
        tbc = ndqb(&tp->t_outq, 0);

#if IPL_ZS != IPL_TTY
        (void)splzs();
#endif

        zst->zst_tba = tba;
        zst->zst_tbc = tbc;
        SET(tp->t_state, TS_BUSY);
        zst->zst_tx_busy = 1;

        do {
                rr0 = zs_read_csr(cs);
                if ((rr0 & ZSRR0_TX_READY) == 0)
                        break;

                zs_write_data(cs, *zst->zst_tba);
                zst->zst_tbc--;
                zst->zst_tba++;
        } while (zst->zst_tbc > 0);

out:
        splx(s);
}

/*
 * Stop output, e.g., for ^S or output flush.
 */
int
zsstop(struct tty *tp, int flag)
{
        struct zstty_softc *zst = zs_device_lookup(&zstty_cd, ZSUNIT(tp->t_dev));
        int s;

        s = splzs();
        if (ISSET(tp->t_state, TS_BUSY)) {
                /* Stop transmitting at the next chunk. */
                zst->zst_tbc = 0;
                zst->zst_heldtbc = 0;
                if (!ISSET(tp->t_state, TS_TTSTOP))
                        SET(tp->t_state, TS_FLUSH);
        }
        splx(s);
        return 0;
}

/*
 * Set ZS tty parameters from termios.
 * XXX - Should just copy the whole termios after
 * making sure all the changes could be done.
 */
int
zsparam(struct tty *tp, struct termios *t)
{
        struct zstty_softc *zst = zs_device_lookup(&zstty_cd, ZSUNIT(tp->t_dev));
        struct zs_chanstate *cs = zst->zst_cs;
        int ospeed;
        tcflag_t cflag;
        uint8_t tmp3, tmp4, tmp5;
        int s, error;

        ospeed = t->c_ospeed;
        cflag = t->c_cflag;

        /* Check requested parameters. */
        if (ospeed < 0)
                return (EINVAL);
        if (t->c_ispeed && t->c_ispeed != ospeed)
                return (EINVAL);

        /*
         * For the console, always force CLOCAL and !HUPCL, so that the port
         * is always active.
         */
        if (ISSET(zst->zst_swflags, TIOCFLAG_SOFTCAR) ||
            ISSET(zst->zst_hwflags, ZS_HWFLAG_CONSOLE)) {
                SET(cflag, CLOCAL);
                CLR(cflag, HUPCL);
        }

        /*
         * Only whack the UART when params change.
         * Some callers need to clear tp->t_ospeed
         * to make sure initialization gets done.
         */
        if (tp->t_ospeed == ospeed &&
            tp->t_cflag == cflag)
                return (0);

        /*
         * Call MD functions to deal with changed
         * clock modes or H/W flow control modes.
         * The BRG divisor is set now. (reg 12,13)
         */
        error = zs_set_speed(cs, ospeed);
        if (error)
                return (error);
        error = zs_set_modes(cs, cflag);
        if (error)
                return (error);

        /*
         * Block interrupts so that state will not
         * be altered until we are done setting it up.
         *
         * Initial values in cs_preg are set before
         * our attach routine is called.  The master
         * interrupt enable is handled by zsc.c
         *
         */
        s = splzs();

        /*
         * Recalculate which status ints to enable.
         */
        zs_maskintr(zst);

        /* Recompute character size bits. */
        tmp3 = cs->cs_preg[3];
        tmp5 = cs->cs_preg[5];
        CLR(tmp3, ZSWR3_RXSIZE);
        CLR(tmp5, ZSWR5_TXSIZE);
        switch (ISSET(cflag, CSIZE)) {
        case CS5:
                SET(tmp3, ZSWR3_RX_5);
                SET(tmp5, ZSWR5_TX_5);
                break;
        case CS6:
                SET(tmp3, ZSWR3_RX_6);
                SET(tmp5, ZSWR5_TX_6);
                break;
        case CS7:
                SET(tmp3, ZSWR3_RX_7);
                SET(tmp5, ZSWR5_TX_7);
                break;
        case CS8:
                SET(tmp3, ZSWR3_RX_8);
                SET(tmp5, ZSWR5_TX_8);
                break;
        }
        cs->cs_preg[3] = tmp3;
        cs->cs_preg[5] = tmp5;

        /*
         * Recompute the stop bits and parity bits.  Note that
         * zs_set_speed() may have set clock selection bits etc.
         * in wr4, so those must preserved.
         */
        tmp4 = cs->cs_preg[4];
        CLR(tmp4, ZSWR4_SBMASK | ZSWR4_PARMASK);
        if (ISSET(cflag, CSTOPB))
                SET(tmp4, ZSWR4_TWOSB);
        else
                SET(tmp4, ZSWR4_ONESB);
        if (!ISSET(cflag, PARODD))
                SET(tmp4, ZSWR4_EVENP);
        if (ISSET(cflag, PARENB))
                SET(tmp4, ZSWR4_PARENB);
        cs->cs_preg[4] = tmp4;

        /* And copy to tty. */
        tp->t_ispeed = 0;
        tp->t_ospeed = ospeed;
        tp->t_cflag = cflag;

        /*
         * If nothing is being transmitted, set up new current values,
         * else mark them as pending.
         */
        if (!cs->cs_heldchange) {
                if (zst->zst_tx_busy) {
                        zst->zst_heldtbc = zst->zst_tbc;
                        zst->zst_tbc = 0;
                        cs->cs_heldchange = 1;
                } else
                        zs_loadchannelregs(cs);
        }

        /*
         * If hardware flow control is disabled, turn off the buffer water
         * marks and unblock any soft flow control state.  Otherwise, enable
         * the water marks.
         */
        if (!ISSET(cflag, CHWFLOW)) {
                zst->zst_r_hiwat = 0;
                zst->zst_r_lowat = 0;
                if (ISSET(zst->zst_rx_flags, RX_TTY_OVERFLOWED)) {
                        CLR(zst->zst_rx_flags, RX_TTY_OVERFLOWED);
                        zst->zst_rx_ready = 1;
                        cs->cs_softreq = 1;
                }
                if (ISSET(zst->zst_rx_flags, RX_TTY_BLOCKED|RX_IBUF_BLOCKED)) {
                        CLR(zst->zst_rx_flags, RX_TTY_BLOCKED|RX_IBUF_BLOCKED);
                        zs_hwiflow(zst);
                }
        } else {
                zst->zst_r_hiwat = zstty_rbuf_hiwat;
                zst->zst_r_lowat = zstty_rbuf_lowat;
        }

        /*
         * Force a recheck of the hardware carrier and flow control status,
         * since we may have changed which bits we're looking at.
         */
        zstty_stint(cs, 1);

        splx(s);

        /*
         * If hardware flow control is disabled, unblock any hard flow control
         * state.
         */
        if (!ISSET(cflag, CHWFLOW)) {
                if (zst->zst_tx_stopped) {
                        zst->zst_tx_stopped = 0;
                        zsstart(tp);
                }
        }

        zstty_softint(cs);

        return (0);
}

/*
 * Compute interrupt enable bits and set in the pending bits. Called both
 * in zsparam() and when PPS (pulse per second timing) state changes.
 * Must be called at splzs().
 */
void
zs_maskintr(struct zstty_softc *zst)
{
        struct zs_chanstate *cs = zst->zst_cs;
        uint8_t tmp15;

        cs->cs_rr0_mask = cs->cs_rr0_cts | cs->cs_rr0_dcd;
        if (zst->zst_ppsmask != 0)
                cs->cs_rr0_mask |= cs->cs_rr0_pps;
        tmp15 = cs->cs_preg[15];
        if (ISSET(cs->cs_rr0_mask, ZSRR0_DCD))
                SET(tmp15, ZSWR15_DCD_IE);
        else
                CLR(tmp15, ZSWR15_DCD_IE);
        if (ISSET(cs->cs_rr0_mask, ZSRR0_CTS))
                SET(tmp15, ZSWR15_CTS_IE);
        else
                CLR(tmp15, ZSWR15_CTS_IE);
        cs->cs_preg[15] = tmp15;
}


/*
 * Raise or lower modem control (DTR/RTS) signals.  If a character is
 * in transmission, the change is deferred.
 * Called at splzs().
 */
void
zs_modem(struct zstty_softc *zst, int onoff)
{
        struct zs_chanstate *cs = zst->zst_cs, *ccs;

        if (cs->cs_wr5_dtr == 0)
                return;

        ccs = (cs->cs_ctl_chan != NULL ? cs->cs_ctl_chan : cs);

        if (onoff)
                SET(ccs->cs_preg[5], cs->cs_wr5_dtr);
        else
                CLR(ccs->cs_preg[5], cs->cs_wr5_dtr);

        if (!cs->cs_heldchange) {
                if (zst->zst_tx_busy) {
                        zst->zst_heldtbc = zst->zst_tbc;
                        zst->zst_tbc = 0;
                        cs->cs_heldchange = 1;
                } else
                        zs_loadchannelregs(cs);
        }
}

/*
 * Set modem bits.
 * Called at splzs().
 */
void
tiocm_to_zs(struct zstty_softc *zst, u_long how, int ttybits)
{
        struct zs_chanstate *cs = zst->zst_cs, *ccs;
        uint8_t zsbits;

        ccs = (cs->cs_ctl_chan != NULL ? cs->cs_ctl_chan : cs);

        zsbits = 0;
        if (ISSET(ttybits, TIOCM_DTR))
                SET(zsbits, ZSWR5_DTR);
        if (ISSET(ttybits, TIOCM_RTS))
                SET(zsbits, ZSWR5_RTS);

        switch (how) {
        case TIOCMBIC:
                CLR(ccs->cs_preg[5], zsbits);
                break;

        case TIOCMBIS:
                SET(ccs->cs_preg[5], zsbits);
                break;

        case TIOCMSET:
                CLR(ccs->cs_preg[5], ZSWR5_RTS | ZSWR5_DTR);
                SET(ccs->cs_preg[5], zsbits);
                break;
        }

        if (!cs->cs_heldchange) {
                if (zst->zst_tx_busy) {
                        zst->zst_heldtbc = zst->zst_tbc;
                        zst->zst_tbc = 0;
                        cs->cs_heldchange = 1;
                } else
                        zs_loadchannelregs(cs);
        }
}

/*
 * Get modem bits.
 * Called at splzs().
 */
int
zs_to_tiocm(struct zstty_softc *zst)
{
        struct zs_chanstate *cs = zst->zst_cs, *ccs;
        uint8_t zsbits;
        int ttybits = 0;

        ccs = (cs->cs_ctl_chan != NULL ? cs->cs_ctl_chan : cs);

        zsbits = ccs->cs_preg[5];
        if (ISSET(zsbits, ZSWR5_DTR))
                SET(ttybits, TIOCM_DTR);
        if (ISSET(zsbits, ZSWR5_RTS))
                SET(ttybits, TIOCM_RTS);

        zsbits = cs->cs_rr0;
        if (ISSET(zsbits, ZSRR0_DCD))
                SET(ttybits, TIOCM_CD);
        if (ISSET(zsbits, ZSRR0_CTS))
                SET(ttybits, TIOCM_CTS);

        return (ttybits);
}

/*
 * Try to block or unblock input using hardware flow-control.
 * This is called by kern/tty.c if MDMBUF|CRTSCTS is set, and
 * if this function returns non-zero, the TS_TBLOCK flag will
 * be set or cleared according to the "block" arg passed.
 */
int
zshwiflow(struct tty *tp, int block)
{
        struct zstty_softc *zst = zs_device_lookup(&zstty_cd, ZSUNIT(tp->t_dev));
        struct zs_chanstate *cs = zst->zst_cs;
        int s;

        if (cs->cs_wr5_rts == 0)
                return (0);

        s = splzs();
        if (block) {
                if (!ISSET(zst->zst_rx_flags, RX_TTY_BLOCKED)) {
                        SET(zst->zst_rx_flags, RX_TTY_BLOCKED);
                        zs_hwiflow(zst);
                }
        } else {
                if (ISSET(zst->zst_rx_flags, RX_TTY_OVERFLOWED)) {
                        CLR(zst->zst_rx_flags, RX_TTY_OVERFLOWED);
                        zst->zst_rx_ready = 1;
                        cs->cs_softreq = 1;
                }
                if (ISSET(zst->zst_rx_flags, RX_TTY_BLOCKED)) {
                        CLR(zst->zst_rx_flags, RX_TTY_BLOCKED);
                        zs_hwiflow(zst);
                }
        }
        splx(s);
        return (1);
}

/*
 * Internal version of zshwiflow
 * Called at splzs()
 */
void
zs_hwiflow(struct zstty_softc *zst)
{
        struct zs_chanstate *cs = zst->zst_cs, *ccs;

        if (cs->cs_wr5_rts == 0)
                return;

        ccs = (cs->cs_ctl_chan != NULL ? cs->cs_ctl_chan : cs);

        if (ISSET(zst->zst_rx_flags, RX_ANY_BLOCK)) {
                CLR(ccs->cs_preg[5], cs->cs_wr5_rts);
                CLR(ccs->cs_creg[5], cs->cs_wr5_rts);
        } else {
                SET(ccs->cs_preg[5], cs->cs_wr5_rts);
                SET(ccs->cs_creg[5], cs->cs_wr5_rts);
        }
        zs_write_reg(ccs, 5, ccs->cs_creg[5]);
}


/****************************************************************
 * Interface to the lower layer (zscc)
 ****************************************************************/

void zstty_rxsoft(struct zstty_softc *, struct tty *);
void zstty_txsoft(struct zstty_softc *, struct tty *);
void zstty_stsoft(struct zstty_softc *, struct tty *);
void zstty_diag(void *);

/*
 * Receiver Ready interrupt.
 * Called at splzs().
 */
void
zstty_rxint(struct zs_chanstate *cs)
{
        struct zstty_softc *zst = cs->cs_private;
        uint8_t *put, *end;
        u_int cc;
        uint8_t rr0, rr1, c;

        end = zst->zst_ebuf;
        put = zst->zst_rbput;
        cc = zst->zst_rbavail;

        while (cc > 0) {
                /*
                 * First read the status, because reading the received char
                 * destroys the status of this char.
                 */
                rr1 = zs_read_reg(cs, 1);
                c = zs_read_data(cs);

                if (ISSET(rr1, ZSRR1_FE | ZSRR1_DO | ZSRR1_PE)) {
                        /* Clear the receive error. */
                        zs_write_csr(cs, ZSWR0_RESET_ERRORS);
                }

                put[0] = c;
                put[1] = rr1;
                put += 2;
                if (put >= end)
                        put = zst->zst_rbuf;
                cc--;

                rr0 = zs_read_csr(cs);
                if (!ISSET(rr0, ZSRR0_RX_READY))
                        break;
        }

        /*
         * Current string of incoming characters ended because
         * no more data was available or we ran out of space.
         * Schedule a receive event if any data was received.
         * If we're out of space, turn off receive interrupts.
         */
        zst->zst_rbput = put;
        zst->zst_rbavail = cc;
        if (!ISSET(zst->zst_rx_flags, RX_TTY_OVERFLOWED)) {
                zst->zst_rx_ready = 1;
                cs->cs_softreq = 1;
        }

        /*
         * See if we are in danger of overflowing a buffer. If
         * so, use hardware flow control to ease the pressure.
         */
        if (!ISSET(zst->zst_rx_flags, RX_IBUF_BLOCKED) &&
            cc < zst->zst_r_hiwat) {
                SET(zst->zst_rx_flags, RX_IBUF_BLOCKED);
                zs_hwiflow(zst);
        }

        /*
         * If we're out of space, disable receive interrupts
         * until the queue has drained a bit.
         */
        if (!cc) {
                SET(zst->zst_rx_flags, RX_IBUF_OVERFLOWED);
                CLR(cs->cs_preg[1], ZSWR1_RIE);
                cs->cs_creg[1] = cs->cs_preg[1];
                zs_write_reg(cs, 1, cs->cs_creg[1]);
        }
}

/*
 * Transmitter Ready interrupt.
 * Called at splzs().
 */
void
zstty_txint(struct zs_chanstate *cs)
{
        struct zstty_softc *zst = cs->cs_private;
        int rr0;

        zs_write_csr(cs, ZSWR0_RESET_TXINT);

        /*
         * If we've delayed a parameter change, do it now, and restart
         * output.
         */
        if (cs->cs_heldchange) {
                zs_loadchannelregs(cs);
                cs->cs_heldchange = 0;
                zst->zst_tbc = zst->zst_heldtbc;
                zst->zst_heldtbc = 0;
        }

        while (zst->zst_tbc > 0) {
                rr0 = zs_read_csr(cs);
                if ((rr0 & ZSRR0_TX_READY) == 0)
                        break;

                zs_write_data(cs, *zst->zst_tba);
                zst->zst_tbc--;
                zst->zst_tba++;
        }

        if (zst->zst_tbc == 0) {
                if (zst->zst_tx_busy) {
                        zst->zst_tx_busy = 0;
                        zst->zst_tx_done = 1;
                        cs->cs_softreq = 1;
                }
        }
}

#ifdef DDB
#include <ddb/db_var.h>
#define DB_CONSOLE      db_console
#else
#define DB_CONSOLE      0
#endif

/*
 * Status Change interrupt.
 * Called at splzs().
 */
void
zstty_stint(struct zs_chanstate *cs, int force)
{
        struct zstty_softc *zst = cs->cs_private;
        struct tty *tp = zst->zst_tty;
        uint8_t rr0, delta;

        rr0 = zs_read_csr(cs);
        zs_write_csr(cs, ZSWR0_RESET_STATUS);

        /*
         * Check here for console break, so that we can abort
         * even when interrupts are locking up the machine.
         */
        if ((zst->zst_hwflags & ZS_HWFLAG_CONSOLE_INPUT) &&
            ISSET(rr0, ZSRR0_BREAK) && DB_CONSOLE)
                zs_abort(cs);

        if (!force)
                delta = rr0 ^ cs->cs_rr0;
        else
                delta = cs->cs_rr0_mask;

        ttytstamp(tp, cs->cs_rr0 & ZSRR0_CTS, rr0 & ZSRR0_CTS,
            cs->cs_rr0 & ZSRR0_DCD, rr0 & ZSRR0_DCD);

        cs->cs_rr0 = rr0;

        if (ISSET(delta, cs->cs_rr0_mask)) {
                SET(cs->cs_rr0_delta, delta);

                /*
                 * Stop output immediately if we lose the output
                 * flow control signal or carrier detect.
                 */
                if (ISSET(~rr0, cs->cs_rr0_mask)) {
                        zst->zst_tbc = 0;
                        zst->zst_heldtbc = 0;
                }

                zst->zst_st_check = 1;
                cs->cs_softreq = 1;
        }
}

void
zstty_diag(void *arg)
{
        struct zstty_softc *zst = arg;
        int overflows, floods;
        int s;

        s = splzs();
        overflows = zst->zst_overflows;
        zst->zst_overflows = 0;
        floods = zst->zst_floods;
        zst->zst_floods = 0;
        zst->zst_errors = 0;
        splx(s);

        log(LOG_WARNING, "%s: %d silo overflow%s, %d ibuf flood%s\n",
            zst->zst_dev.dv_xname,
            overflows, overflows == 1 ? "" : "s",
            floods, floods == 1 ? "" : "s");
}

void
zstty_rxsoft(struct zstty_softc *zst, struct tty *tp)
{
        struct zs_chanstate *cs = zst->zst_cs;
        int (*rint)(int, struct tty *) = linesw[tp->t_line].l_rint;
        uint8_t *get, *end;
        u_int cc, scc;
        uint8_t rr1;
        int code;
        int s;

        end = zst->zst_ebuf;
        get = zst->zst_rbget;
        scc = cc = zstty_rbuf_size - zst->zst_rbavail;

        if (cc == zstty_rbuf_size) {
                zst->zst_floods++;
                if (zst->zst_errors++ == 0)
                        timeout_add_sec(&zst->zst_diag_ch, 60);
        }

        /* If not yet open, drop the entire buffer content here */
        if (!ISSET(tp->t_state, TS_ISOPEN)) {
                get += cc << 1;
                if (get >= end)
                        get -= zstty_rbuf_size << 1;
                cc = 0;
        }
        while (cc) {
                code = get[0];
                rr1 = get[1];
                if (ISSET(rr1, ZSRR1_DO | ZSRR1_FE | ZSRR1_PE)) {
                        if (ISSET(rr1, ZSRR1_DO)) {
                                zst->zst_overflows++;
                                if (zst->zst_errors++ == 0)
                                        timeout_add_sec(&zst->zst_diag_ch, 60);
                        }
                        if (ISSET(rr1, ZSRR1_FE))
                                SET(code, TTY_FE);
                        if (ISSET(rr1, ZSRR1_PE))
                                SET(code, TTY_PE);
                }
                if ((*rint)(code, tp) == -1) {
                        /*
                         * The line discipline's buffer is out of space.
                         */
                        if (!ISSET(zst->zst_rx_flags, RX_TTY_BLOCKED)) {
                                /*
                                 * We're either not using flow control, or the
                                 * line discipline didn't tell us to block for
                                 * some reason.  Either way, we have no way to
                                 * know when there's more space available, so
                                 * just drop the rest of the data.
                                 */
                                get += cc << 1;
                                if (get >= end)
                                        get -= zstty_rbuf_size << 1;
                                cc = 0;
                        } else {
                                /*
                                 * Don't schedule any more receive processing
                                 * until the line discipline tells us there's
                                 * space available (through comhwiflow()).
                                 * Leave the rest of the data in the input
                                 * buffer.
                                 */
                                SET(zst->zst_rx_flags, RX_TTY_OVERFLOWED);
                        }
                        break;
                }
                get += 2;
                if (get >= end)
                        get = zst->zst_rbuf;
                cc--;
        }

        if (cc != scc) {
                zst->zst_rbget = get;
                s = splzs();
                cc = zst->zst_rbavail += scc - cc;
                /* Buffers should be ok again, release possible block. */
                if (cc >= zst->zst_r_lowat) {
                        if (ISSET(zst->zst_rx_flags, RX_IBUF_OVERFLOWED)) {
                                CLR(zst->zst_rx_flags, RX_IBUF_OVERFLOWED);
                                SET(cs->cs_preg[1], ZSWR1_RIE);
                                cs->cs_creg[1] = cs->cs_preg[1];
                                zs_write_reg(cs, 1, cs->cs_creg[1]);
                        }
                        if (ISSET(zst->zst_rx_flags, RX_IBUF_BLOCKED)) {
                                CLR(zst->zst_rx_flags, RX_IBUF_BLOCKED);
                                zs_hwiflow(zst);
                        }
                }
                splx(s);
        }
}

void
zstty_txsoft(struct zstty_softc *zst, struct tty *tp)
{
        int s;

        CLR(tp->t_state, TS_BUSY);
        if (ISSET(tp->t_state, TS_FLUSH))
                CLR(tp->t_state, TS_FLUSH);
        else {
                s = splzs();
                ndflush(&tp->t_outq, (int)(zst->zst_tba - tp->t_outq.c_cf));
                splx(s);
        }
        (*linesw[tp->t_line].l_start)(tp);
}

void
zstty_stsoft(struct zstty_softc *zst, struct tty *tp)
{
        struct zs_chanstate *cs = zst->zst_cs;
        uint8_t rr0, delta;
        int s;

        s = splzs();
        rr0 = cs->cs_rr0;
        delta = cs->cs_rr0_delta;
        cs->cs_rr0_delta = 0;
        splx(s);

        if (ISSET(delta, cs->cs_rr0_dcd)) {
                /*
                 * Inform the tty layer that carrier detect changed.
                 */
                (void)(*linesw[tp->t_line].l_modem)(tp, ISSET(rr0, ZSRR0_DCD));
        }

        if (ISSET(delta, cs->cs_rr0_cts)) {
                /* Block or unblock output according to flow control. */
                if (ISSET(rr0, cs->cs_rr0_cts)) {
                        zst->zst_tx_stopped = 0;
                        (*linesw[tp->t_line].l_start)(tp);
                } else {
                        zst->zst_tx_stopped = 1;
                }
        }
}

/*
 * Software interrupt.  Called at zssoft
 *
 * The main job to be done here is to empty the input ring
 * by passing its contents up to the tty layer.  The ring is
 * always emptied during this operation, therefore the ring
 * must not be larger than the space after "high water" in
 * the tty layer, or the tty layer might drop our input.
 *
 * Note: an "input blockage" condition is assumed to exist if
 * EITHER the TS_TBLOCK flag or zst_rx_blocked flag is set.
 */
void
zstty_softint(struct zs_chanstate *cs)
{
        struct zstty_softc *zst = cs->cs_private;
        struct tty *tp = zst->zst_tty;
        int s;

        s = spltty();

        if (zst->zst_rx_ready) {
                zst->zst_rx_ready = 0;
                zstty_rxsoft(zst, tp);
        }

        if (zst->zst_st_check) {
                zst->zst_st_check = 0;
                zstty_stsoft(zst, tp);
        }

        if (zst->zst_tx_done) {
                zst->zst_tx_done = 0;
                zstty_txsoft(zst, tp);
        }

        splx(s);
}

struct zsops zsops_tty = {
        zstty_rxint,    /* receive char available */
        zstty_stint,    /* external/status */
        zstty_txint,    /* xmit buffer empty */
        zstty_softint,  /* process software interrupt */
};