Reduce timeout frequency from `hz' to 0 if no ports are open or to 1 if

no ports are active, provided there are no polled ports and no
`LOSESOUTINTS' ports.  Do a little more in the interrupt handler instead.
This is a little less efficient if there are are many active ports but
a little more efficient otherwise.  Polled ports are ones with no irq
specified (as before).  `LOSESOUTINTS' ports are ones with 0x08 set in
their config flags.  Unless this flag is set, it will now take up to one
second to recover from lost output interrupts, if any.  Some 8250s and
16450s lose output interrupts.

Improve output buffering: copy the clist buffer to 2 linear buffers if
necessary and possible instead of to 1.  Handle an arbitrary queue of
buffers in the interrupt handler.  Check for waking up sleepers after
copying characters out of the clist buffer instead of before.

Delay translation of TIOCM_DTR to MCR_DTR etc. so that the top level
routines are more machine independent.

Fix bogus device register in unused code.

1 files changed, 236 insertions, 142 deletions

diff --git a/sys/dev/sio/sio.c b/sys/dev/sio/sio.c
index 4ae58cd..50719aa 100644
--- a/sys/dev/sio/sio.c
+++ b/sys/dev/sio/sio.c
@@ -31,7 +31,7 @@
  * SUCH DAMAGE.
  *
  *	from: @(#)com.c	7.5 (Berkeley) 5/16/91
- *	$Id: sio.c,v 1.98 1995/05/11 19:26:19 rgrimes Exp $
+ *	$Id: sio.c,v 1.99 1995/05/30 08:03:06 rgrimes Exp $
  */
 
 #include "sio.h"
@@ -74,7 +74,8 @@
 #define	TSA_CARR_ON(tp)		((void *)&(tp)->t_rawq)
 #define	TSA_OCOMPLETE(tp)	((void *)&(tp)->t_outq)
 #define	TSA_OLOWAT(tp)		((void *)&(tp)->t_outq)
-void
+static	void	termioschars	__P((struct termios *t));
+static void
 termioschars(t)
 	struct termios *t;
 {
@@ -103,6 +104,7 @@ termioschars(t)
 #define	COM_NOTAST4(dev)	((dev)->id_flags & 0x04)
 #endif /* COM_MULTIPORT */
 
+#define	COM_LOSESOUTINTS(dev)	((dev)->id_flags & 0x08)
 #define	COM_NOFIFO(dev)		((dev)->id_flags & 0x02)
 #define	COM_VERBOSE(dev)	((dev)->id_flags & 0x80)
 
@@ -127,7 +129,8 @@ termioschars(t)
  * off the low bits.
  *
  * The following com and tty flags correspond closely:
- *	CS_BUSY		= TS_BUSY (maintained by comstart() and comflush())
+ *	CS_BUSY		= TS_BUSY (maintained by comstart(), siopoll() and
+ *				   siostop())
  *	CS_TTGO		= ~TS_TTSTOP (maintained by comstart() and siostop())
  *	CS_CTS_OFLOW	= CCTS_OFLOW (maintained by comparam())
  *	CS_RTS_IFLOW	= CRTS_IFLOW (maintained by comparam())
@@ -160,6 +163,14 @@ static	char const * const	error_desc[] = {
 typedef u_int	Port_t;		/* hardware port */
 typedef u_char	bool_t;		/* boolean */
 
+/* queue of linear buffers */
+struct lbq {
+	u_char	*l_head;	/* next char to process */
+	u_char	*l_tail;	/* one past the last char to process */
+	struct lbq *l_next;	/* next in queue */
+	bool_t	l_queued;	/* nonzero if queued */
+};
+
 /* com device structure */
 struct com_s {
 	u_char	state;		/* miscellaneous flag bits */
@@ -169,12 +180,14 @@ struct com_s {
 	u_char	ftl_init;	/* ftl_max for next open() */
 	u_char	ftl_max;	/* maximum ftl for curent open() */
 	bool_t	hasfifo;	/* nonzero for 16550 UARTs */
+	bool_t	loses_outints;	/* nonzero if device loses output interrupts */
 	u_char	mcr_image;	/* copy of value written to MCR */
 #ifdef COM_MULTIPORT
 	bool_t	multiport;	/* is this unit part of a multiport device? */
 #endif /* COM_MULTIPORT */
 	bool_t	no_irq;		/* nonzero if irq is not attached */
 	bool_t	poll;		/* nonzero if polling is required */
+	bool_t	poll_output;	/* nonzero if polling for output is required */
 	int	unit;		/* unit	number */
 	int	dtr_wait;	/* time to hold DTR down on close (* 1/hz) */
 	u_int	tx_fifo_size;
@@ -195,8 +208,8 @@ struct com_s {
 	u_char	*ihighwater;	/* threshold in input buffer */
 	u_char	*iptr;		/* next free spot in input buffer */
 
-	u_char	*obufend;	/* end of output buffer */
-	u_char	*optr;		/* next char to output */
+	struct lbq	obufq;	/* head of queue of output buffers */
+	struct lbq	obufs[2];	/* output buffers */
 
 	Port_t	data_port;	/* i/o ports */
 	Port_t	int_id_port;
@@ -232,9 +245,11 @@ struct com_s {
 	u_char	ibuf2[2 * RS_IBUFSIZE];
 
 	/*
-	 * Output buffer.  Someday we should avoid copying.  Twice.
+	 * Data area for output buffers.  Someday we should build the output
+	 * buffer queue without copying data.
 	 */
-	u_char	obuf[256];
+	u_char	obuf1[256];
+	u_char	obuf2[256];
 };
 
 /*
@@ -264,17 +279,17 @@ struct tty *siodevtotty	__P((dev_t dev));
 
 static	int	sioattach	__P((struct isa_device *dev));
 static	timeout_t siodtrwakeup;
-static	void	comflush	__P((struct com_s *com));
 static	void	comhardclose	__P((struct com_s *com));
 static	void	siointr1	__P((struct com_s *com));
-static	void	commctl		__P((struct com_s *com, int bits, int how));
+static	int	commctl		__P((struct com_s *com, int bits, int how));
 static	int	comparam	__P((struct tty *tp, struct termios *t));
 static	int	sioprobe	__P((struct isa_device *dev));
 static	void	sioregisterdev	__P((struct isa_device *id));
+static	void	siosettimeout	__P((void));
 static	void	comstart	__P((struct tty *tp));
 static	timeout_t comwakeup;
-static	int	tiocm_xxx2mcr	__P((int tiocm_xxx));
-static	void	disc_optim	__P((struct tty	*tp, struct termios *t,	struct com_s *com));
+static	void	disc_optim	__P((struct tty	*tp, struct termios *t,
+				     struct com_s *com));
 
 #ifdef DSI_SOFT_MODEM
 static  int 	LoadSoftModem   __P((int unit,int base_io, u_long size, u_char *ptr));
@@ -301,12 +316,13 @@ static	int	comconsole = CONUNIT;
 static	speed_t	comdefaultrate = TTYDEF_SPEED;
 static	u_int	com_events;	/* input chars + weighted output completions */
 static	int	commajor;
+static	int	sio_timeout;
+static	int	sio_timeouts_until_log;
 #if 0 /* XXX TK2.0 */
-struct tty	*sio_tty[NSIO];
+static struct tty	*sio_tty[NSIO];
 #else
-/* must be not static, used by pstat -t */
-struct tty	sio_tty[NSIO];
-int             nsio_tty = NSIO;
+static struct tty	sio_tty[NSIO];
+static	int	nsio_tty = NSIO;
 #endif
 
 #ifdef KGDB
@@ -562,7 +578,6 @@ sioattach(isdp)
 	struct isa_device	*isdp;
 {
 	struct com_s	*com;
-	static bool_t	comwakeup_started = FALSE;
 	Port_t		iobase;
 	int		s;
 	int		unit;
@@ -590,11 +605,15 @@ sioattach(isdp)
 	com->unit = unit;
 	com->cfcr_image = CFCR_8BITS;
 	com->dtr_wait = 3 * hz;
+	com->loses_outints = COM_LOSESOUTINTS(isdp) != 0;
 	com->no_irq = isdp->id_irq == 0;
 	com->tx_fifo_size = 1;
 	com->iptr = com->ibuf = com->ibuf1;
 	com->ibufend = com->ibuf1 + RS_IBUFSIZE;
 	com->ihighwater = com->ibuf1 + RS_IHIGHWATER;
+	com->obufs[0].l_head = com->obuf1;
+	com->obufs[1].l_head = com->obuf2;
+
 	com->iobase = iobase;
 	com->data_port = iobase + com_data;
 	com->int_id_port = iobase + com_iir;
@@ -728,7 +747,7 @@ determined_type: ;
 			outb(iobase + com_dlbl, divisor & 0xFF);
 			outb(iobase + com_dlbh, (u_int) divisor >> 8);
 			outb(iobase + com_cfcr, CFCR_8BITS);
-			outb(com->modem_status_port,
+			outb(com->modem_ctl_port,
 			     com->mcr_image |= MCR_DTR | MCR_RTS);
 
 			if (kgdb_debug_init) {
@@ -747,14 +766,9 @@ determined_type: ;
 	s = spltty();
 	com_addr(unit) = com;
 	splx(s);
-	if (!comwakeup_started) {
-		comwakeup((void *)NULL);
-		comwakeup_started = TRUE;
-	}
 	return (1);
 }
 
-/* ARGSUSED */
 int
 sioopen(dev, flag, mode, p)
 	dev_t		dev;
@@ -832,9 +846,10 @@ open_top:
 		tp->t_dev = dev;
 		tp->t_termios = mynor & CALLOUT_MASK
 				? com->it_out : com->it_in;
-		commctl(com, MCR_DTR | MCR_RTS, DMSET);
+		(void)commctl(com, TIOCM_DTR | TIOCM_RTS, DMSET);
 		com->ftl_max = com->ftl_init;
 		com->poll = com->no_irq;
+		com->poll_output = com->loses_outints;
 		++com->wopeners;
 		error = comparam(tp, &tp->t_termios);
 		--com->wopeners;
@@ -873,8 +888,8 @@ open_top:
 		disable_intr();
 		(void) inb(com->line_status_port);
 		(void) inb(com->data_port);
-			com->prev_modem_status =
-			com->last_modem_status = inb(com->modem_status_port);
+		com->prev_modem_status = com->last_modem_status
+		    = inb(com->modem_status_port);
 		outb(iobase + com_ier, IER_ERXRDY | IER_ETXRDY | IER_ERLS
 				       | IER_EMSC);
 		enable_intr();
@@ -884,6 +899,13 @@ open_top:
 		 * callin opens get woken up and resume sleeping on "siobi"
 		 * instead of "siodcd".
 		 */
+		/*
+		 * XXX `mynor & CALLOUT_MASK' should be
+		 * `tp->t_cflag & (SOFT_CARRIER | TRAPDOOR_CARRIER) where
+		 * TRAPDOOR_CARRIER is the default initial state for callout
+		 * devices and SOFT_CARRIER is like CLOCAL except it hides
+		 * the true carrier.
+		 */
 		if (com->prev_modem_status & MSR_DCD || mynor & CALLOUT_MASK)
 			(*linesw[tp->t_line].l_modem)(tp, 1);
 	}
@@ -900,9 +922,10 @@ open_top:
 		goto open_top;
 	}
 	error =	(*linesw[tp->t_line].l_open)(dev, tp);
-	disc_optim(tp, &(tp->t_termios), com);
+	disc_optim(tp, &tp->t_termios, com);
 	if (tp->t_state & TS_ISOPEN && mynor & CALLOUT_MASK)
 		com->active_out = TRUE;
+	siosettimeout();
 out:
 	splx(s);
 	if (!(tp->t_state & TS_ISOPEN) && com->wopeners == 0)
@@ -910,7 +933,6 @@ out:
 	return (error);
 }
 
-/*ARGSUSED*/
 int
 sioclose(dev, flag, mode, p)
 	dev_t		dev;
@@ -930,10 +952,11 @@ sioclose(dev, flag, mode, p)
 	tp = com->tp;
 	s = spltty();
 	(*linesw[tp->t_line].l_close)(tp, flag);
-	disc_optim(tp, &(tp->t_termios), com);
+	disc_optim(tp, &tp->t_termios, com);
 	siostop(tp, FREAD | FWRITE);
 	comhardclose(com);
 	ttyclose(tp);
+	siosettimeout();
 	splx(s);
 	return (0);
 }
@@ -951,6 +974,7 @@ comhardclose(com)
 	iobase = com->iobase;
 	s = spltty();
 	com->poll = FALSE;
+	com->poll_output = FALSE;
 	com->do_timestamp = 0;
 	outb(iobase + com_cfcr, com->cfcr_image &= ~CFCR_SBREAK);
 #ifdef KGDB
@@ -972,7 +996,7 @@ comhardclose(com)
 		       && !(com->prev_modem_status & MSR_DCD)
 		       && !(com->it_in.c_cflag & CLOCAL)
 		    || !(tp->t_state & TS_ISOPEN)) {
-			commctl(com, MCR_RTS, DMSET);
+			(void)commctl(com, TIOCM_DTR, DMBIC);
 			if (com->dtr_wait != 0) {
 				timeout(siodtrwakeup, com, com->dtr_wait);
 				com->state |= CS_DTR_OFF;
@@ -1097,7 +1121,7 @@ siointr(unit)
 
 static void
 siointr1(com)
-	struct com_s *com;
+	struct com_s	*com;
 {
 	u_char	line_status;
 	u_char	modem_status;
@@ -1165,6 +1189,7 @@ siointr1(com)
 				CE_RECORD(com, CE_INTERRUPT_BUF_OVERFLOW);
 			else {
 				++com_events;
+				schedsofttty();
 #if 0 /* for testing input latency vs efficiency */
 if (com->iptr - com->ibuf == 8)
 	setsofttty();
@@ -1179,7 +1204,7 @@ if (com->iptr - com->ibuf == 8)
 				if (line_status & LSR_OE)
 					CE_RECORD(com, CE_OVERRUN);
 			}
-		cont:
+cont:
 			/*
 			 * "& 0x7F" is to avoid the gcc-1.40 generating a slow
 			 * jump from the top of the loop to here
@@ -1214,12 +1239,12 @@ if (com->iptr - com->ibuf == 8)
 
 		/* output queued and everything ready? */
 		if (line_status & LSR_TXRDY
-		    && com->state >= (CS_ODEVREADY | CS_BUSY | CS_TTGO)) {
-			ioptr = com->optr;
+		    && com->state >= (CS_BUSY | CS_TTGO | CS_ODEVREADY)) {
+			ioptr = com->obufq.l_head;
 			if (com->tx_fifo_size > 1) {
 				u_int	ocount;
 
-				ocount = com->obufend - ioptr;
+				ocount = com->obufq.l_tail - ioptr;
 				if (ocount > com->tx_fifo_size)
 					ocount = com->tx_fifo_size;
 				com->bytes_out += ocount;
@@ -1230,12 +1255,26 @@ if (com->iptr - com->ibuf == 8)
 				outb(com->data_port, *ioptr++);
 				++com->bytes_out;
 			}
-			com->optr = ioptr;
-			if (ioptr >= com->obufend) {
-				/* output just completed */
-				com_events += LOTS_OF_EVENTS;
-				com->state ^= (CS_ODONE | CS_BUSY);
-				setsofttty();	/* handle at high level ASAP */
+			com->obufq.l_head = ioptr;
+			if (ioptr >= com->obufq.l_tail) {
+				struct lbq	*qp;
+
+				qp = com->obufq.l_next;
+				qp->l_queued = FALSE;
+				qp = qp->l_next;
+				if (qp != NULL) {
+					com->obufq.l_head = qp->l_head;
+					com->obufq.l_tail = qp->l_tail;
+					com->obufq.l_next = qp;
+				} else {
+					/* output just completed */
+					com->state &= ~CS_BUSY;
+				}
+				if (!(com->state & CS_ODONE)) {
+					com_events += LOTS_OF_EVENTS;
+					com->state |= CS_ODONE;
+					setsofttty();	/* handle at high level ASAP */
+				}
 			}
 		}
 
@@ -1247,20 +1286,6 @@ if (com->iptr - com->ibuf == 8)
 	}
 }
 
-static int
-tiocm_xxx2mcr(tiocm_xxx)
-	int	tiocm_xxx;
-{
-	int	mcr;
-
-	mcr = 0;
-	if (tiocm_xxx & TIOCM_DTR)
-		mcr |= MCR_DTR;
-	if (tiocm_xxx & TIOCM_RTS)
-		mcr |= MCR_RTS;
-	return (mcr);
-}
-
 int
 sioioctl(dev, cmd, data, flag, p)
 	dev_t		dev;
@@ -1272,11 +1297,8 @@ sioioctl(dev, cmd, data, flag, p)
 	struct com_s	*com;
 	int		error;
 	Port_t		iobase;
-	int		mcr;
-	int		msr;
 	int		mynor;
 	int		s;
-	int		tiocm_xxx;
 	struct tty	*tp;
 #if defined(COMPAT_43) || defined(COMPAT_SUNOS)
 	int		oldcmd;
@@ -1384,7 +1406,7 @@ sioioctl(dev, cmd, data, flag, p)
 		return (error);
 	s = spltty();
 	error = ttioctl(tp, cmd, data, flag);
-	disc_optim(tp, &(tp->t_termios), com);
+	disc_optim(tp, &tp->t_termios, com);
 	if (error >= 0) {
 		splx(s);
 		return (error);
@@ -1397,42 +1419,22 @@ sioioctl(dev, cmd, data, flag, p)
 		outb(iobase + com_cfcr, com->cfcr_image &= ~CFCR_SBREAK);
 		break;
 	case TIOCSDTR:
-		commctl(com, MCR_DTR, DMBIS);
+		(void)commctl(com, TIOCM_DTR, DMBIS);
 		break;
 	case TIOCCDTR:
-		commctl(com, MCR_DTR, DMBIC);
+		(void)commctl(com, TIOCM_DTR, DMBIC);
 		break;
 	case TIOCMSET:
-		commctl(com, tiocm_xxx2mcr(*(int *)data), DMSET);
+		(void)commctl(com, *(int *)data, DMSET);
 		break;
 	case TIOCMBIS:
-		commctl(com, tiocm_xxx2mcr(*(int *)data), DMBIS);
+		(void)commctl(com, *(int *)data, DMBIS);
 		break;
 	case TIOCMBIC:
-		commctl(com, tiocm_xxx2mcr(*(int *)data), DMBIC);
+		(void)commctl(com, *(int *)data, DMBIC);
 		break;
 	case TIOCMGET:
-		tiocm_xxx = TIOCM_LE;	/* XXX - always enabled while open */
-		mcr = com->mcr_image;
-		if (mcr & MCR_DTR)
-			tiocm_xxx |= TIOCM_DTR;
-		if (mcr & MCR_RTS)
-			tiocm_xxx |= TIOCM_RTS;
-		msr = com->prev_modem_status;
-		if (msr & MSR_CTS)
-			tiocm_xxx |= TIOCM_CTS;
-		if (msr & MSR_DCD)
-			tiocm_xxx |= TIOCM_CD;
-		if (msr & MSR_DSR)
-			tiocm_xxx |= TIOCM_DSR;
-		/*
-		 * XXX - MSR_RI is naturally volatile, and we make MSR_TERI
-		 * more volatile by reading the modem status a lot.  Perhaps
-		 * we should latch both bits until the status is read here.
-		 */
-		if (msr & (MSR_RI | MSR_TERI))
-			tiocm_xxx |= TIOCM_RI;
-		*(int *)data = tiocm_xxx;
+		*(int *)data = commctl(com, 0, DMGET);
 		break;
 	case TIOCMSDTRWAIT:
 		/* must be root since the wait applies to following logins */
@@ -1458,19 +1460,6 @@ sioioctl(dev, cmd, data, flag, p)
 	return (0);
 }
 
-/* cancel pending output */
-static void
-comflush(com)
-	struct com_s	*com;
-{
-	disable_intr();
-	if (com->state & CS_ODONE)
-		com_events -= LOTS_OF_EVENTS;
-	com->state &= ~(CS_ODONE | CS_BUSY);
-	enable_intr();
-	com->tp->t_state &= ~TS_BUSY;
-}
-
 void
 siopoll()
 {
@@ -1565,7 +1554,12 @@ repeat:
 					(tp, com->prev_modem_status & MSR_DCD);
 		}
 		if (com->state & CS_ODONE) {
-			comflush(com);
+			disable_intr();
+			com_events -= LOTS_OF_EVENTS;
+			com->state &= ~CS_ODONE;
+			if (!(com->state & CS_BUSY))
+				com->tp->t_state &= ~TS_BUSY;
+			enable_intr();
 			(*linesw[tp->t_line].l_start)(tp);
 		}
 		if (incc <= 0 || !(tp->t_state & TS_ISOPEN))
@@ -1581,7 +1575,7 @@ repeat:
 		     * Only have it in standard one now.
 		     */
 		    && linesw[tp->t_line].l_rint == ttyinput) {
-			int	putc_status = FALSE;
+			int	putc_status = 0;
 
 			if ((tp->t_iflag & IXOFF
 			     && tp->t_cc[VSTOP] != _POSIX_VDISABLE
@@ -1658,10 +1652,12 @@ comparam(tp, t)
 	int		s;
 	int		unit;
 
-	/* check requested parameters */
-	divisor = ttspeedtab(t->c_ospeed, comspeedtab);
+	/* do historical conversions */
 	if (t->c_ispeed == 0)
 		t->c_ispeed = t->c_ospeed;
+
+	/* check requested parameters */
+	divisor = ttspeedtab(t->c_ospeed, comspeedtab);
 	if (divisor < 0 || divisor > 0 && t->c_ispeed != t->c_ospeed)
 		return (EINVAL);
 
@@ -1671,9 +1667,9 @@ comparam(tp, t)
 	iobase = com->iobase;
 	s = spltty();
 	if (divisor == 0)
-		commctl(com, MCR_DTR, DMBIC);	/* hang up line */
+		(void)commctl(com, TIOCM_DTR, DMBIC);	/* hang up line */
 	else
-		commctl(com, MCR_DTR, DMBIS);
+		(void)commctl(com, TIOCM_DTR, DMBIS);
 	cflag = t->c_cflag;
 	switch (cflag & CSIZE) {
 	case CS5:
@@ -1770,13 +1766,14 @@ retry:
 	 * XXX - worth handling MDMBUF (DCD) flow control at the lowest level?
 	 * Now has 10+ msec latency, while CTS flow has 50- usec latency.
 	 */
-	com->state &= ~CS_CTS_OFLOW;
 	com->state |= CS_ODEVREADY;
+	com->state &= ~CS_CTS_OFLOW;
 	if (cflag & CCTS_OFLOW) {
 		com->state |= CS_CTS_OFLOW;
 		if (!(com->last_modem_status & MSR_CTS))
 			com->state &= ~CS_ODEVREADY;
 	}
+	/* XXX shouldn't call functions while intrs are disabled. */
 	disc_optim(tp, t, com);
 	/*
 	 * Recover from fiddling with CS_TTGO.  We used to call siointr1()
@@ -1820,8 +1817,61 @@ comstart(tp)
 			outb(com->modem_ctl_port, com->mcr_image |= MCR_RTS);
 	}
 	enable_intr();
-	if (tp->t_state & (TS_TIMEOUT | TS_TTSTOP))
-		goto out;
+	if (tp->t_state & (TS_TIMEOUT | TS_TTSTOP)) {
+		splx(s);
+		return;
+	}
+	if (tp->t_outq.c_cc != 0) {
+		struct lbq	*qp;
+		struct lbq	*next;
+
+		if (!com->obufs[0].l_queued) {
+			com->obufs[0].l_tail
+			    = com->obuf1 + q_to_b(&tp->t_outq, com->obuf1,
+						  sizeof com->obuf1);
+			com->obufs[0].l_next = NULL;
+			com->obufs[0].l_queued = TRUE;
+			disable_intr();
+			if (com->state & CS_BUSY) {
+				qp = com->obufq.l_next;
+				while ((next = qp->l_next) != NULL)
+					qp = next;
+				qp->l_next = &com->obufs[0];
+			} else {
+				com->obufq.l_head = com->obufs[0].l_head;
+				com->obufq.l_tail = com->obufs[0].l_tail;
+				com->obufq.l_next = &com->obufs[0];
+				com->state |= CS_BUSY;
+			}
+			enable_intr();
+		}
+		if (tp->t_outq.c_cc != 0 && !com->obufs[1].l_queued) {
+			com->obufs[1].l_tail
+			    = com->obuf2 + q_to_b(&tp->t_outq, com->obuf2,
+						  sizeof com->obuf2);
+			com->obufs[1].l_next = NULL;
+			com->obufs[1].l_queued = TRUE;
+			disable_intr();
+			if (com->state & CS_BUSY) {
+				qp = com->obufq.l_next;
+				while ((next = qp->l_next) != NULL)
+					qp = next;
+				qp->l_next = &com->obufs[1];
+			} else {
+				com->obufq.l_head = com->obufs[1].l_head;
+				com->obufq.l_tail = com->obufs[1].l_tail;
+				com->obufq.l_next = &com->obufs[1];
+				com->state |= CS_BUSY;
+			}
+			enable_intr();
+		}
+		tp->t_state |= TS_BUSY;
+	}
+	disable_intr();
+	if (com->state >= (CS_BUSY | CS_TTGO))
+		siointr1(com);	/* fake interrupt to start output */
+	enable_intr();
+
 #if 0 /* XXX TK2.0 */
 	if (tp->t_state & (TS_SO_OCOMPLETE | TS_SO_OLOWAT) || tp->t_wsel)
 		ttwwakeup(tp);
@@ -1834,22 +1884,6 @@ comstart(tp)
 		selwakeup(&tp->t_wsel);
 	}
 #endif
-	if (tp->t_state & TS_BUSY) {
-		disable_intr();
-		siointr1(com);
-		enable_intr();
-	} else if (tp->t_outq.c_cc != 0) {
-		u_int	ocount;
-
-		tp->t_state |= TS_BUSY;
-		ocount = q_to_b(&tp->t_outq, com->obuf, sizeof com->obuf);
-		disable_intr();
-		com->obufend = (com->optr = com->obuf) + ocount;
-		com->state |= CS_BUSY;
-		siointr1(com);	/* fake interrupt to start output */
-		enable_intr();
-	}
-out:
 	splx(s);
 }
 
@@ -1861,9 +1895,15 @@ siostop(tp, rw)
 	struct com_s	*com;
 
 	com = com_addr(DEV_TO_UNIT(tp->t_dev));
-	if (rw & FWRITE)
-		comflush(com);
 	disable_intr();
+	if (rw & FWRITE) {
+		com->obufs[0].l_queued = FALSE;
+		com->obufs[1].l_queued = FALSE;
+		if (com->state & CS_ODONE)
+			com_events -= LOTS_OF_EVENTS;
+		com->state &= ~(CS_ODONE | CS_BUSY);
+		com->tp->t_state &= ~TS_BUSY;
+	}
 	if (rw & FREAD) {
 		com_events -= (com->iptr - com->ibuf);
 		com->iptr = com->ibuf;
@@ -1873,6 +1913,8 @@ siostop(tp, rw)
 	else
 		com->state |= CS_TTGO;
 	enable_intr();
+
+	/* XXX should clear h/w fifos too. */
 }
 
 struct tty *
@@ -1891,45 +1933,99 @@ siodevtotty(dev)
 	return (&sio_tty[unit]);
 }
 
-static void
+static int
 commctl(com, bits, how)
 	struct com_s	*com;
 	int		bits;
 	int		how;
 {
+	int	mcr;
+	int	msr;
+
+	if (how == DMGET) {
+		bits = TIOCM_LE;	/* XXX - always enabled while open */
+		mcr = com->mcr_image;
+		if (mcr & MCR_DTR)
+			bits |= TIOCM_DTR;
+		if (mcr & MCR_RTS)
+			bits |= TIOCM_RTS;
+		msr = com->prev_modem_status;
+		if (msr & MSR_CTS)
+			bits |= TIOCM_CTS;
+		if (msr & MSR_DCD)
+			bits |= TIOCM_CD;
+		if (msr & MSR_DSR)
+			bits |= TIOCM_DSR;
+		/*
+		 * XXX - MSR_RI is naturally volatile, and we make MSR_TERI
+		 * more volatile by reading the modem status a lot.  Perhaps
+		 * we should latch both bits until the status is read here.
+		 */
+		if (msr & (MSR_RI | MSR_TERI))
+			bits |= TIOCM_RI;
+		return (bits);
+	}
+	mcr = 0;
+	if (bits & TIOCM_DTR)
+		mcr |= MCR_DTR;
+	if (bits & TIOCM_RTS)
+		mcr |= MCR_RTS;
 	disable_intr();
 	switch (how) {
 	case DMSET:
 		outb(com->modem_ctl_port,
-		     com->mcr_image = bits | (com->mcr_image & MCR_IENABLE));
+		     com->mcr_image = mcr | (com->mcr_image & MCR_IENABLE));
 		break;
 	case DMBIS:
-		outb(com->modem_ctl_port, com->mcr_image |= bits);
+		outb(com->modem_ctl_port, com->mcr_image |= mcr);
 		break;
 	case DMBIC:
-		outb(com->modem_ctl_port, com->mcr_image &= ~bits);
+		outb(com->modem_ctl_port, com->mcr_image &= ~mcr);
 		break;
 	}
 	enable_intr();
+	return (0);
 }
 
 static void
-comwakeup(chan)
-	void	*chan;
+siosettimeout()
 {
 	struct com_s	*com;
-	static	int	log_countdown = 1;
+	bool_t		someopen;
 	int		unit;
 
-	timeout(comwakeup, (caddr_t)NULL, hz > 200 ? hz / 200 : 1);
+	/*
+	 * Set our timeout period to 1 second if no polled devices are open.
+	 * Otherwise set it to max(1/200, 1/hz).
+	 * Enable timeouts iff some device is open.
+	 */
+	untimeout(comwakeup, (void *)NULL);
+	sio_timeout = hz;
+	someopen = FALSE;
+	for (unit = 0; unit < NSIO; ++unit) {
+		com = com_addr(unit);
+		if (com != NULL && com->tp != NULL
+		    && com->tp->t_state & TS_ISOPEN) {
+			someopen = TRUE;
+			if (com->poll || com->poll_output) {
+				sio_timeout = hz > 200 ? hz / 200 : 1;
+				break;
+			}
+		}
+	}
+	sio_timeouts_until_log = hz / sio_timeout;
+	if (someopen)
+		timeout(comwakeup, (void *)NULL, sio_timeout);
+}
 
-	if (com_events != 0) {
-		int	s;
+static void
+comwakeup(chan)
+	void	*chan;
+{
+	struct com_s	*com;
+	int		unit;
 
-		s = splsofttty();
-		siopoll();
-		splx(s);
-	}
+	timeout(comwakeup, (void *)NULL, sio_timeout);
 
 	/*
 	 * Recover from lost output interrupts.
@@ -1948,9 +2044,9 @@ comwakeup(chan)
 	/*
 	 * Check for and log errors, but not too often.
 	 */
-	if (--log_countdown > 0)
+	if (--sio_timeouts_until_log > 0)
 		return;
-	log_countdown = hz > 200 ? 200 : hz;
+	sio_timeouts_until_log = sio_timeout;
 	for (unit = 0; unit < NSIO; ++unit) {
 		int	errnum;
 
@@ -2005,7 +2101,6 @@ disc_optim(tp, t, com)
 	struct termios	*t;
 	struct com_s	*com;
 {
-
 	if (!(t->c_iflag & (ICRNL | IGNCR | IMAXBEL | INLCR | ISTRIP
 			   | IXOFF | IXON))
 	    && (!(t->c_iflag & BRKINT) || (t->c_iflag & IGNBRK))
@@ -2144,7 +2239,6 @@ siocnprobe(cp)
 		cp->cn_pri = CN_REMOTE;	/* Force a serial port console */
 	else
 		cp->cn_pri = CN_NORMAL;
-
 }
 
 void