YAMFsio.c (1.227-1.228: set up input buffering dynamically).

2 files changed, 378 insertions, 232 deletions

diff --git a/sys/dev/cy/cy.c b/sys/dev/cy/cy.c
index 42f6794..e513c05 100644
--- a/sys/dev/cy/cy.c
+++ b/sys/dev/cy/cy.c
@@ -27,7 +27,7 @@
  * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
  * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  *
- *	$Id: cy.c,v 1.84 1999/01/28 01:59:53 dillon Exp $
+ *	$Id: cy.c,v 1.85 1999/01/30 12:17:33 phk Exp $
  */
 
 #include "opt_compat.h"
@@ -131,6 +131,7 @@
 #define	siodevtotty	cydevtotty
 #define	siodriver	cydriver
 #define	siodtrwakeup	cydtrwakeup
+#define	sioinput	cyinput
 #define	siointr		cyintr
 #define	siointr1	cyintr1
 #define	sioioctl	cyioctl
@@ -139,6 +140,7 @@
 #define	sioprobe	cyprobe
 #define	sioread		cyread
 #define	siosettimeout	cysettimeout
+#define	siosetwater	cysetwater
 #define	siostop		cystop
 #define	siowrite	cywrite
 #define	sio_registered	cy_registered
@@ -164,7 +166,6 @@
 #define	ETC_BREAK_ENDED		4
 
 #define	LOTS_OF_EVENTS	64	/* helps separate urgent events from input */
-#define	RS_IBUFSIZE	256
 
 #define	CALLOUT_MASK		0x80
 #define	CONTROL_MASK		0x60
@@ -176,18 +177,6 @@
 				 | (((mynor) & 0xff) & ~MINOR_MAGIC_MASK))
 
 /*
- * Input buffer watermarks.
- * The external device is asked to stop sending when the buffer exactly reaches
- * high water, or when the high level requests it.
- * The high level is notified immediately (rather than at a later clock tick)
- * when this watermark is reached.
- * The buffer size is chosen so the watermark should almost never be reached.
- * The low watermark is invisibly 0 since the buffer is always emptied all at
- * once.
- */
-#define	RS_IHIGHWATER (3 * RS_IBUFSIZE / 4)
-
-/*
  * com state bits.
  * (CS_BUSY | CS_TTGO) and (CS_BUSY | CS_TTGO | CS_ODEVREADY) must be higher
  * than the other bits so that they can be tested as a group without masking
@@ -284,8 +273,11 @@ struct com_s {
 	u_char	hotchar;	/* ldisc-specific char to be handled ASAP */
 	u_char	*ibuf;		/* start of input buffer */
 	u_char	*ibufend;	/* end of input buffer */
+	u_char	*ibufold;	/* old input buffer, to be freed */
 	u_char	*ihighwater;	/* threshold in input buffer */
 	u_char	*iptr;		/* next free spot in input buffer */
+	int	ibufsize;	/* size of ibuf (not include error bytes) */
+	int	ierroff;	/* offset of error bytes in ibuf */
 
 	struct lbq	obufq;	/* head of queue of output buffers */
 	struct lbq	obufs[2];	/* output buffers */
@@ -327,14 +319,6 @@ struct com_s {
 	u_char	intr_enable;	/* CD1400 SRER shadow */
 
 	/*
-	 * Ping-pong input buffers.  The extra factor of 2 in the sizes is
-	 * to allow for an error byte for each input byte.
-	 */
-#define	CE_INPUT_OFFSET		RS_IBUFSIZE
-	u_char	ibuf1[2 * RS_IBUFSIZE];
-	u_char	ibuf2[2 * RS_IBUFSIZE];
-
-	/*
 	 * Data area for output buffers.  Someday we should build the output
 	 * buffer queue without copying data.
 	 */
@@ -363,6 +347,7 @@ static	int	cd_getreg	__P((struct com_s *com, int reg));
 static	void	cd_setreg	__P((struct com_s *com, int reg, int val));
 static	timeout_t siodtrwakeup;
 static	void	comhardclose	__P((struct com_s *com));
+static	void	sioinput	__P((struct com_s *com));
 #if 0
 static	void	siointr1	__P((struct com_s *com));
 #endif
@@ -371,6 +356,7 @@ static	int	comparam	__P((struct tty *tp, struct termios *t));
 static	swihand_t siopoll;
 static	int	sioprobe	__P((struct isa_device *dev));
 static	void	siosettimeout	__P((void));
+static	int	siosetwater	__P((struct com_s *com, speed_t speed));
 static	int	comspeed	__P((speed_t speed, u_long cy_clock,
 				     int *prescaler_io));
 static	void	comstart	__P((struct tty *tp));
@@ -592,9 +578,6 @@ cyattach_common(cy_iobase, cy_align)
 				com->mcr_rts_reg = CD1400_MSVR1;
 			}
 	com->dtr_wait = 3 * hz;
-	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;
 
@@ -620,6 +603,12 @@ cyattach_common(cy_iobase, cy_align)
 		com->it_in.c_lflag = TTYDEF_LFLAG;
 		com->lt_out.c_cflag = com->lt_in.c_cflag = CLOCAL;
 	}
+	if (siosetwater(com, com->it_in.c_ispeed) != 0) {
+		enable_intr();
+		free(com, M_DEVBUF);
+		return (0);
+	}
+	enable_intr();
 	termioschars(&com->it_in);
 	com->it_in.c_ispeed = com->it_in.c_ospeed = comdefaultrate;
 	com->it_out = com->it_in;
@@ -745,9 +734,6 @@ open_top:
 		tp->t_dev = dev;
 		tp->t_termios = mynor & CALLOUT_MASK
 				? com->it_out : com->it_in;
-		tp->t_ififosize = 2 * RS_IBUFSIZE;
-		tp->t_ispeedwat = (speed_t)-1;
-		tp->t_ospeedwat = (speed_t)-1;
 
 		/* Encode per-board unit in LIVR for access in intr routines. */
 		cd_setreg(com, CD1400_LIVR,
@@ -1028,6 +1014,93 @@ siodtrwakeup(chan)
 	wakeup(&com->dtr_wait);
 }
 
+static void
+sioinput(com)
+	struct com_s	*com;
+{
+	u_char		*buf;
+	int		incc;
+	u_char		line_status;
+	int		recv_data;
+	struct tty	*tp;
+
+	buf = com->ibuf;
+	tp = com->tp;
+	if (!(tp->t_state & TS_ISOPEN)) {
+		com_events -= (com->iptr - com->ibuf);
+		com->iptr = com->ibuf;
+		return;
+	}
+	if (tp->t_state & TS_CAN_BYPASS_L_RINT) {
+		/*
+		 * Avoid the grotesquely inefficient lineswitch routine
+		 * (ttyinput) in "raw" mode.  It usually takes about 450
+		 * instructions (that's without canonical processing or echo!).
+		 * slinput is reasonably fast (usually 40 instructions plus
+		 * call overhead).
+		 */
+		do {
+			enable_intr();
+			incc = com->iptr - buf;
+			if (tp->t_rawq.c_cc + incc > tp->t_ihiwat
+			    && (com->state & CS_RTS_IFLOW
+				|| tp->t_iflag & IXOFF)
+			    && !(tp->t_state & TS_TBLOCK))
+				ttyblock(tp);
+			com->delta_error_counts[CE_TTY_BUF_OVERFLOW]
+				+= b_to_q((char *)buf, incc, &tp->t_rawq);
+			buf += incc;
+			tk_nin += incc;
+			tk_rawcc += incc;
+			tp->t_rawcc += incc;
+			ttwakeup(tp);
+			if (tp->t_state & TS_TTSTOP
+			    && (tp->t_iflag & IXANY
+				|| tp->t_cc[VSTART] == tp->t_cc[VSTOP])) {
+				tp->t_state &= ~TS_TTSTOP;
+				tp->t_lflag &= ~FLUSHO;
+				comstart(tp);
+			}
+			disable_intr();
+		} while (buf < com->iptr);
+	} else {
+		do {
+			enable_intr();
+			line_status = buf[com->ierroff];
+			recv_data = *buf++;
+			if (line_status
+			    & (LSR_BI | LSR_FE | LSR_OE | LSR_PE)) {
+				if (line_status & LSR_BI)
+					recv_data |= TTY_BI;
+				if (line_status & LSR_FE)
+					recv_data |= TTY_FE;
+				if (line_status & LSR_OE)
+					recv_data |= TTY_OE;
+				if (line_status & LSR_PE)
+					recv_data |= TTY_PE;
+			}
+			(*linesw[tp->t_line].l_rint)(recv_data, tp);
+			disable_intr();
+		} while (buf < com->iptr);
+	}
+	com_events -= (com->iptr - com->ibuf);
+	com->iptr = com->ibuf;
+
+	/*
+	 * There is now room for another low-level buffer full of input,
+	 * so enable RTS if it is now disabled and there is room in the
+	 * high-level buffer.
+	 */
+	if ((com->state & CS_RTS_IFLOW) && !(com->mcr_image & com->mcr_rts) &&
+	    !(tp->t_state & TS_TBLOCK))
+#if 0
+		outb(com->modem_ctl_port, com->mcr_image |= MCR_RTS);
+#else
+		cd_setreg(com, com->mcr_rts_reg,
+			  com->mcr_image |= com->mcr_rts);
+#endif
+}
+
 void
 siointr(unit)
 	int	unit;
@@ -1134,7 +1207,7 @@ siointr(unit)
 					microtime(&com->timestamp);
 				++com_events;
 				ioptr[0] = recv_data;
-				ioptr[CE_INPUT_OFFSET] = line_status;
+				ioptr[com->ierroff] = line_status;
 				com->iptr = ++ioptr;
 				if (ioptr == com->ihighwater
 				    && com->state & CS_RTS_IFLOW)
@@ -1177,7 +1250,7 @@ siointr(unit)
 							setsofttty();
 #endif
 						ioptr[0] = recv_data;
-						ioptr[CE_INPUT_OFFSET] = 0;
+						ioptr[com->ierroff] = 0;
 						++ioptr;
 					} while (--ifree != 0);
 				}
@@ -1217,7 +1290,7 @@ siointr(unit)
 						setsofttty();
 #endif
 					ioptr[0] = recv_data;
-					ioptr[CE_INPUT_OFFSET] = 0;
+					ioptr[com->ierroff] = 0;
 					++ioptr;
 				} while (--count != 0);
 			}
@@ -1687,9 +1760,7 @@ siopoll()
 		return;
 repeat:
 	for (unit = 0; unit < NSIO; ++unit) {
-		u_char		*buf;
 		struct com_s	*com;
-		u_char		*ibuf;
 		int		incc;
 		struct tty	*tp;
 
@@ -1718,43 +1789,11 @@ repeat:
 				    unit, incc);
 			continue;
 		}
-
-		/* switch the role of the low-level input buffers */
-		if (com->iptr == (ibuf = com->ibuf)) {
-			buf = NULL;     /* not used, but compiler can't tell */
-			incc = 0;
-		} else {
-			buf = ibuf;
+		if (com->iptr != com->ibuf) {
 			disable_intr();
-			incc = com->iptr - buf;
-			com_events -= incc;
-			if (ibuf == com->ibuf1)
-				ibuf = com->ibuf2;
-			else
-				ibuf = com->ibuf1;
-			com->ibufend = ibuf + RS_IBUFSIZE;
-			com->ihighwater = ibuf + RS_IHIGHWATER;
-			com->iptr = ibuf;
-
-			/*
-			 * There is now room for another low-level buffer full
-			 * of input, so enable RTS if it is now disabled and
-			 * there is room in the high-level buffer.
-			 */
-			if ((com->state & CS_RTS_IFLOW)
-			    && !(com->mcr_image & com->mcr_rts)
-			    && !(tp->t_state & TS_TBLOCK))
-#if 0
-				outb(com->modem_ctl_port,
-				     com->mcr_image |= MCR_RTS);
-#else
-				cd_setreg(com, com->mcr_rts_reg,
-					  com->mcr_image |= com->mcr_rts);
-#endif
+			sioinput(com);
 			enable_intr();
-			com->ibuf = ibuf;
 		}
-
 		if (com->state & CS_CHECKMSR) {
 			u_char	delta_modem_status;
 
@@ -1791,55 +1830,6 @@ repeat:
 			enable_intr();
 			(*linesw[tp->t_line].l_start)(tp);
 		}
-		if (incc <= 0 || !(tp->t_state & TS_ISOPEN))
-			continue;
-		/*
-		 * Avoid the grotesquely inefficient lineswitch routine
-		 * (ttyinput) in "raw" mode.  It usually takes about 450
-		 * instructions (that's without canonical processing or echo!).
-		 * slinput is reasonably fast (usually 40 instructions plus
-		 * call overhead).
-		 */
-		if (tp->t_state & TS_CAN_BYPASS_L_RINT) {
-			if (tp->t_rawq.c_cc + incc > tp->t_ihiwat
-			    && (com->state & CS_RTS_IFLOW
-				|| tp->t_iflag & IXOFF)
-			    && !(tp->t_state & TS_TBLOCK))
-				ttyblock(tp);
-			tk_nin += incc;
-			tk_rawcc += incc;
-			tp->t_rawcc += incc;
-			com->delta_error_counts[CE_TTY_BUF_OVERFLOW]
-				+= b_to_q((char *)buf, incc, &tp->t_rawq);
-			ttwakeup(tp);
-			if (tp->t_state & TS_TTSTOP
-			    && (tp->t_iflag & IXANY
-				|| tp->t_cc[VSTART] == tp->t_cc[VSTOP])) {
-				tp->t_state &= ~TS_TTSTOP;
-				tp->t_lflag &= ~FLUSHO;
-				comstart(tp);
-			}
-		} else {
-			do {
-				u_char	line_status;
-				int	recv_data;
-
-				line_status = (u_char) buf[CE_INPUT_OFFSET];
-				recv_data = (u_char) *buf++;
-				if (line_status
-				    & (LSR_BI | LSR_FE | LSR_OE | LSR_PE)) {
-					if (line_status & LSR_BI)
-						recv_data |= TTY_BI;
-					if (line_status & LSR_FE)
-						recv_data |= TTY_FE;
-					if (line_status & LSR_OE)
-						recv_data |= TTY_OE;
-					if (line_status & LSR_PE)
-						recv_data |= TTY_PE;
-				}
-				(*linesw[tp->t_line].l_rint)(recv_data, tp);
-			} while (--incc > 0);
-		}
 		if (com_events == 0)
 			break;
 	}
@@ -1890,6 +1880,15 @@ comparam(tp, t)
 	else
 		(void)commctl(com, TIOCM_DTR, DMBIS);
 
+	/*
+	 * This returns with interrupts disabled so that we can complete
+	 * the speed change atomically.
+	 */
+	(void) siosetwater(com, t->c_ispeed);
+
+	/* XXX we don't actually change the speed atomically. */
+	enable_intr();
+
 	if (idivisor != 0) {
 		cd_setreg(com, CD1400_RBPR, idivisor);
 		cd_setreg(com, CD1400_RCOR, iprescaler);
@@ -2204,6 +2203,80 @@ comparam(tp, t)
 	enable_intr();
 	splx(s);
 	comstart(tp);
+	if (com->ibufold != NULL) {
+		free(com->ibufold, M_DEVBUF);
+		com->ibufold = NULL;
+	}
+	return (0);
+}
+
+static int
+siosetwater(com, speed)
+	struct com_s	*com;
+	speed_t		speed;
+{
+	int		cp4ticks;
+	u_char		*ibuf;
+	int		ibufsize;
+	struct tty	*tp;
+
+	/*
+	 * Make the buffer size large enough to handle a softtty interrupt
+	 * latency of about 2 ticks without loss of throughput or data
+	 * (about 3 ticks if input flow control is not used or not honoured,
+	 * but a bit less for CS5-CS7 modes).
+	 */
+	cp4ticks = speed / 10 / hz * 4;
+	for (ibufsize = 128; ibufsize < cp4ticks;)
+		ibufsize <<= 1;
+	if (ibufsize == com->ibufsize) {
+		disable_intr();
+		return (0);
+	}
+
+	/*
+	 * Allocate input buffer.  The extra factor of 2 in the size is
+	 * to allow for an error byte for each input byte.
+	 */
+	ibuf = malloc(2 * ibufsize, M_DEVBUF, M_NOWAIT);
+	if (ibuf == NULL) {
+		disable_intr();
+		return (ENOMEM);
+	}
+
+	/* Initialize non-critical variables. */
+	com->ibufold = com->ibuf;
+	com->ibufsize = ibufsize;
+	tp = com->tp;
+	if (tp != NULL) {
+		tp->t_ififosize = 2 * ibufsize;
+		tp->t_ispeedwat = (speed_t)-1;
+		tp->t_ospeedwat = (speed_t)-1;
+	}
+
+	/*
+	 * Read current input buffer, if any.  Continue with interrupts
+	 * disabled.
+	 */
+	disable_intr();
+	if (com->iptr != com->ibuf)
+		sioinput(com);
+
+	/*-
+	 * Initialize critical variables, including input buffer watermarks.
+	 * The external device is asked to stop sending when the buffer
+	 * exactly reaches high water, or when the high level requests it.
+	 * The high level is notified immediately (rather than at a later
+	 * clock tick) when this watermark is reached.
+	 * The buffer size is chosen so the watermark should almost never
+	 * be reached.
+	 * The low watermark is invisibly 0 since the buffer is always
+	 * emptied all at once.
+	 */
+	com->iptr = com->ibuf = ibuf;
+	com->ibufend = ibuf + ibufsize;
+	com->ierroff = ibufsize;
+	com->ihighwater = ibuf + 3 * ibufsize / 4;
 	return (0);
 }
 
diff --git a/sys/dev/cy/cy_isa.c b/sys/dev/cy/cy_isa.c
index 42f6794..e513c05 100644
--- a/sys/dev/cy/cy_isa.c
+++ b/sys/dev/cy/cy_isa.c
@@ -27,7 +27,7 @@
  * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
  * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  *
- *	$Id: cy.c,v 1.84 1999/01/28 01:59:53 dillon Exp $
+ *	$Id: cy.c,v 1.85 1999/01/30 12:17:33 phk Exp $
  */
 
 #include "opt_compat.h"
@@ -131,6 +131,7 @@
 #define	siodevtotty	cydevtotty
 #define	siodriver	cydriver
 #define	siodtrwakeup	cydtrwakeup
+#define	sioinput	cyinput
 #define	siointr		cyintr
 #define	siointr1	cyintr1
 #define	sioioctl	cyioctl
@@ -139,6 +140,7 @@
 #define	sioprobe	cyprobe
 #define	sioread		cyread
 #define	siosettimeout	cysettimeout
+#define	siosetwater	cysetwater
 #define	siostop		cystop
 #define	siowrite	cywrite
 #define	sio_registered	cy_registered
@@ -164,7 +166,6 @@
 #define	ETC_BREAK_ENDED		4
 
 #define	LOTS_OF_EVENTS	64	/* helps separate urgent events from input */
-#define	RS_IBUFSIZE	256
 
 #define	CALLOUT_MASK		0x80
 #define	CONTROL_MASK		0x60
@@ -176,18 +177,6 @@
 				 | (((mynor) & 0xff) & ~MINOR_MAGIC_MASK))
 
 /*
- * Input buffer watermarks.
- * The external device is asked to stop sending when the buffer exactly reaches
- * high water, or when the high level requests it.
- * The high level is notified immediately (rather than at a later clock tick)
- * when this watermark is reached.
- * The buffer size is chosen so the watermark should almost never be reached.
- * The low watermark is invisibly 0 since the buffer is always emptied all at
- * once.
- */
-#define	RS_IHIGHWATER (3 * RS_IBUFSIZE / 4)
-
-/*
  * com state bits.
  * (CS_BUSY | CS_TTGO) and (CS_BUSY | CS_TTGO | CS_ODEVREADY) must be higher
  * than the other bits so that they can be tested as a group without masking
@@ -284,8 +273,11 @@ struct com_s {
 	u_char	hotchar;	/* ldisc-specific char to be handled ASAP */
 	u_char	*ibuf;		/* start of input buffer */
 	u_char	*ibufend;	/* end of input buffer */
+	u_char	*ibufold;	/* old input buffer, to be freed */
 	u_char	*ihighwater;	/* threshold in input buffer */
 	u_char	*iptr;		/* next free spot in input buffer */
+	int	ibufsize;	/* size of ibuf (not include error bytes) */
+	int	ierroff;	/* offset of error bytes in ibuf */
 
 	struct lbq	obufq;	/* head of queue of output buffers */
 	struct lbq	obufs[2];	/* output buffers */
@@ -327,14 +319,6 @@ struct com_s {
 	u_char	intr_enable;	/* CD1400 SRER shadow */
 
 	/*
-	 * Ping-pong input buffers.  The extra factor of 2 in the sizes is
-	 * to allow for an error byte for each input byte.
-	 */
-#define	CE_INPUT_OFFSET		RS_IBUFSIZE
-	u_char	ibuf1[2 * RS_IBUFSIZE];
-	u_char	ibuf2[2 * RS_IBUFSIZE];
-
-	/*
 	 * Data area for output buffers.  Someday we should build the output
 	 * buffer queue without copying data.
 	 */
@@ -363,6 +347,7 @@ static	int	cd_getreg	__P((struct com_s *com, int reg));
 static	void	cd_setreg	__P((struct com_s *com, int reg, int val));
 static	timeout_t siodtrwakeup;
 static	void	comhardclose	__P((struct com_s *com));
+static	void	sioinput	__P((struct com_s *com));
 #if 0
 static	void	siointr1	__P((struct com_s *com));
 #endif
@@ -371,6 +356,7 @@ static	int	comparam	__P((struct tty *tp, struct termios *t));
 static	swihand_t siopoll;
 static	int	sioprobe	__P((struct isa_device *dev));
 static	void	siosettimeout	__P((void));
+static	int	siosetwater	__P((struct com_s *com, speed_t speed));
 static	int	comspeed	__P((speed_t speed, u_long cy_clock,
 				     int *prescaler_io));
 static	void	comstart	__P((struct tty *tp));
@@ -592,9 +578,6 @@ cyattach_common(cy_iobase, cy_align)
 				com->mcr_rts_reg = CD1400_MSVR1;
 			}
 	com->dtr_wait = 3 * hz;
-	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;
 
@@ -620,6 +603,12 @@ cyattach_common(cy_iobase, cy_align)
 		com->it_in.c_lflag = TTYDEF_LFLAG;
 		com->lt_out.c_cflag = com->lt_in.c_cflag = CLOCAL;
 	}
+	if (siosetwater(com, com->it_in.c_ispeed) != 0) {
+		enable_intr();
+		free(com, M_DEVBUF);
+		return (0);
+	}
+	enable_intr();
 	termioschars(&com->it_in);
 	com->it_in.c_ispeed = com->it_in.c_ospeed = comdefaultrate;
 	com->it_out = com->it_in;
@@ -745,9 +734,6 @@ open_top:
 		tp->t_dev = dev;
 		tp->t_termios = mynor & CALLOUT_MASK
 				? com->it_out : com->it_in;
-		tp->t_ififosize = 2 * RS_IBUFSIZE;
-		tp->t_ispeedwat = (speed_t)-1;
-		tp->t_ospeedwat = (speed_t)-1;
 
 		/* Encode per-board unit in LIVR for access in intr routines. */
 		cd_setreg(com, CD1400_LIVR,
@@ -1028,6 +1014,93 @@ siodtrwakeup(chan)
 	wakeup(&com->dtr_wait);
 }
 
+static void
+sioinput(com)
+	struct com_s	*com;
+{
+	u_char		*buf;
+	int		incc;
+	u_char		line_status;
+	int		recv_data;
+	struct tty	*tp;
+
+	buf = com->ibuf;
+	tp = com->tp;
+	if (!(tp->t_state & TS_ISOPEN)) {
+		com_events -= (com->iptr - com->ibuf);
+		com->iptr = com->ibuf;
+		return;
+	}
+	if (tp->t_state & TS_CAN_BYPASS_L_RINT) {
+		/*
+		 * Avoid the grotesquely inefficient lineswitch routine
+		 * (ttyinput) in "raw" mode.  It usually takes about 450
+		 * instructions (that's without canonical processing or echo!).
+		 * slinput is reasonably fast (usually 40 instructions plus
+		 * call overhead).
+		 */
+		do {
+			enable_intr();
+			incc = com->iptr - buf;
+			if (tp->t_rawq.c_cc + incc > tp->t_ihiwat
+			    && (com->state & CS_RTS_IFLOW
+				|| tp->t_iflag & IXOFF)
+			    && !(tp->t_state & TS_TBLOCK))
+				ttyblock(tp);
+			com->delta_error_counts[CE_TTY_BUF_OVERFLOW]
+				+= b_to_q((char *)buf, incc, &tp->t_rawq);
+			buf += incc;
+			tk_nin += incc;
+			tk_rawcc += incc;
+			tp->t_rawcc += incc;
+			ttwakeup(tp);
+			if (tp->t_state & TS_TTSTOP
+			    && (tp->t_iflag & IXANY
+				|| tp->t_cc[VSTART] == tp->t_cc[VSTOP])) {
+				tp->t_state &= ~TS_TTSTOP;
+				tp->t_lflag &= ~FLUSHO;
+				comstart(tp);
+			}
+			disable_intr();
+		} while (buf < com->iptr);
+	} else {
+		do {
+			enable_intr();
+			line_status = buf[com->ierroff];
+			recv_data = *buf++;
+			if (line_status
+			    & (LSR_BI | LSR_FE | LSR_OE | LSR_PE)) {
+				if (line_status & LSR_BI)
+					recv_data |= TTY_BI;
+				if (line_status & LSR_FE)
+					recv_data |= TTY_FE;
+				if (line_status & LSR_OE)
+					recv_data |= TTY_OE;
+				if (line_status & LSR_PE)
+					recv_data |= TTY_PE;
+			}
+			(*linesw[tp->t_line].l_rint)(recv_data, tp);
+			disable_intr();
+		} while (buf < com->iptr);
+	}
+	com_events -= (com->iptr - com->ibuf);
+	com->iptr = com->ibuf;
+
+	/*
+	 * There is now room for another low-level buffer full of input,
+	 * so enable RTS if it is now disabled and there is room in the
+	 * high-level buffer.
+	 */
+	if ((com->state & CS_RTS_IFLOW) && !(com->mcr_image & com->mcr_rts) &&
+	    !(tp->t_state & TS_TBLOCK))
+#if 0
+		outb(com->modem_ctl_port, com->mcr_image |= MCR_RTS);
+#else
+		cd_setreg(com, com->mcr_rts_reg,
+			  com->mcr_image |= com->mcr_rts);
+#endif
+}
+
 void
 siointr(unit)
 	int	unit;
@@ -1134,7 +1207,7 @@ siointr(unit)
 					microtime(&com->timestamp);
 				++com_events;
 				ioptr[0] = recv_data;
-				ioptr[CE_INPUT_OFFSET] = line_status;
+				ioptr[com->ierroff] = line_status;
 				com->iptr = ++ioptr;
 				if (ioptr == com->ihighwater
 				    && com->state & CS_RTS_IFLOW)
@@ -1177,7 +1250,7 @@ siointr(unit)
 							setsofttty();
 #endif
 						ioptr[0] = recv_data;
-						ioptr[CE_INPUT_OFFSET] = 0;
+						ioptr[com->ierroff] = 0;
 						++ioptr;
 					} while (--ifree != 0);
 				}
@@ -1217,7 +1290,7 @@ siointr(unit)
 						setsofttty();
 #endif
 					ioptr[0] = recv_data;
-					ioptr[CE_INPUT_OFFSET] = 0;
+					ioptr[com->ierroff] = 0;
 					++ioptr;
 				} while (--count != 0);
 			}
@@ -1687,9 +1760,7 @@ siopoll()
 		return;
 repeat:
 	for (unit = 0; unit < NSIO; ++unit) {
-		u_char		*buf;
 		struct com_s	*com;
-		u_char		*ibuf;
 		int		incc;
 		struct tty	*tp;
 
@@ -1718,43 +1789,11 @@ repeat:
 				    unit, incc);
 			continue;
 		}
-
-		/* switch the role of the low-level input buffers */
-		if (com->iptr == (ibuf = com->ibuf)) {
-			buf = NULL;     /* not used, but compiler can't tell */
-			incc = 0;
-		} else {
-			buf = ibuf;
+		if (com->iptr != com->ibuf) {
 			disable_intr();
-			incc = com->iptr - buf;
-			com_events -= incc;
-			if (ibuf == com->ibuf1)
-				ibuf = com->ibuf2;
-			else
-				ibuf = com->ibuf1;
-			com->ibufend = ibuf + RS_IBUFSIZE;
-			com->ihighwater = ibuf + RS_IHIGHWATER;
-			com->iptr = ibuf;
-
-			/*
-			 * There is now room for another low-level buffer full
-			 * of input, so enable RTS if it is now disabled and
-			 * there is room in the high-level buffer.
-			 */
-			if ((com->state & CS_RTS_IFLOW)
-			    && !(com->mcr_image & com->mcr_rts)
-			    && !(tp->t_state & TS_TBLOCK))
-#if 0
-				outb(com->modem_ctl_port,
-				     com->mcr_image |= MCR_RTS);
-#else
-				cd_setreg(com, com->mcr_rts_reg,
-					  com->mcr_image |= com->mcr_rts);
-#endif
+			sioinput(com);
 			enable_intr();
-			com->ibuf = ibuf;
 		}
-
 		if (com->state & CS_CHECKMSR) {
 			u_char	delta_modem_status;
 
@@ -1791,55 +1830,6 @@ repeat:
 			enable_intr();
 			(*linesw[tp->t_line].l_start)(tp);
 		}
-		if (incc <= 0 || !(tp->t_state & TS_ISOPEN))
-			continue;
-		/*
-		 * Avoid the grotesquely inefficient lineswitch routine
-		 * (ttyinput) in "raw" mode.  It usually takes about 450
-		 * instructions (that's without canonical processing or echo!).
-		 * slinput is reasonably fast (usually 40 instructions plus
-		 * call overhead).
-		 */
-		if (tp->t_state & TS_CAN_BYPASS_L_RINT) {
-			if (tp->t_rawq.c_cc + incc > tp->t_ihiwat
-			    && (com->state & CS_RTS_IFLOW
-				|| tp->t_iflag & IXOFF)
-			    && !(tp->t_state & TS_TBLOCK))
-				ttyblock(tp);
-			tk_nin += incc;
-			tk_rawcc += incc;
-			tp->t_rawcc += incc;
-			com->delta_error_counts[CE_TTY_BUF_OVERFLOW]
-				+= b_to_q((char *)buf, incc, &tp->t_rawq);
-			ttwakeup(tp);
-			if (tp->t_state & TS_TTSTOP
-			    && (tp->t_iflag & IXANY
-				|| tp->t_cc[VSTART] == tp->t_cc[VSTOP])) {
-				tp->t_state &= ~TS_TTSTOP;
-				tp->t_lflag &= ~FLUSHO;
-				comstart(tp);
-			}
-		} else {
-			do {
-				u_char	line_status;
-				int	recv_data;
-
-				line_status = (u_char) buf[CE_INPUT_OFFSET];
-				recv_data = (u_char) *buf++;
-				if (line_status
-				    & (LSR_BI | LSR_FE | LSR_OE | LSR_PE)) {
-					if (line_status & LSR_BI)
-						recv_data |= TTY_BI;
-					if (line_status & LSR_FE)
-						recv_data |= TTY_FE;
-					if (line_status & LSR_OE)
-						recv_data |= TTY_OE;
-					if (line_status & LSR_PE)
-						recv_data |= TTY_PE;
-				}
-				(*linesw[tp->t_line].l_rint)(recv_data, tp);
-			} while (--incc > 0);
-		}
 		if (com_events == 0)
 			break;
 	}
@@ -1890,6 +1880,15 @@ comparam(tp, t)
 	else
 		(void)commctl(com, TIOCM_DTR, DMBIS);
 
+	/*
+	 * This returns with interrupts disabled so that we can complete
+	 * the speed change atomically.
+	 */
+	(void) siosetwater(com, t->c_ispeed);
+
+	/* XXX we don't actually change the speed atomically. */
+	enable_intr();
+
 	if (idivisor != 0) {
 		cd_setreg(com, CD1400_RBPR, idivisor);
 		cd_setreg(com, CD1400_RCOR, iprescaler);
@@ -2204,6 +2203,80 @@ comparam(tp, t)
 	enable_intr();
 	splx(s);
 	comstart(tp);
+	if (com->ibufold != NULL) {
+		free(com->ibufold, M_DEVBUF);
+		com->ibufold = NULL;
+	}
+	return (0);
+}
+
+static int
+siosetwater(com, speed)
+	struct com_s	*com;
+	speed_t		speed;
+{
+	int		cp4ticks;
+	u_char		*ibuf;
+	int		ibufsize;
+	struct tty	*tp;
+
+	/*
+	 * Make the buffer size large enough to handle a softtty interrupt
+	 * latency of about 2 ticks without loss of throughput or data
+	 * (about 3 ticks if input flow control is not used or not honoured,
+	 * but a bit less for CS5-CS7 modes).
+	 */
+	cp4ticks = speed / 10 / hz * 4;
+	for (ibufsize = 128; ibufsize < cp4ticks;)
+		ibufsize <<= 1;
+	if (ibufsize == com->ibufsize) {
+		disable_intr();
+		return (0);
+	}
+
+	/*
+	 * Allocate input buffer.  The extra factor of 2 in the size is
+	 * to allow for an error byte for each input byte.
+	 */
+	ibuf = malloc(2 * ibufsize, M_DEVBUF, M_NOWAIT);
+	if (ibuf == NULL) {
+		disable_intr();
+		return (ENOMEM);
+	}
+
+	/* Initialize non-critical variables. */
+	com->ibufold = com->ibuf;
+	com->ibufsize = ibufsize;
+	tp = com->tp;
+	if (tp != NULL) {
+		tp->t_ififosize = 2 * ibufsize;
+		tp->t_ispeedwat = (speed_t)-1;
+		tp->t_ospeedwat = (speed_t)-1;
+	}
+
+	/*
+	 * Read current input buffer, if any.  Continue with interrupts
+	 * disabled.
+	 */
+	disable_intr();
+	if (com->iptr != com->ibuf)
+		sioinput(com);
+
+	/*-
+	 * Initialize critical variables, including input buffer watermarks.
+	 * The external device is asked to stop sending when the buffer
+	 * exactly reaches high water, or when the high level requests it.
+	 * The high level is notified immediately (rather than at a later
+	 * clock tick) when this watermark is reached.
+	 * The buffer size is chosen so the watermark should almost never
+	 * be reached.
+	 * The low watermark is invisibly 0 since the buffer is always
+	 * emptied all at once.
+	 */
+	com->iptr = com->ibuf = ibuf;
+	com->ibufend = ibuf + ibufsize;
+	com->ierroff = ibufsize;
+	com->ihighwater = ibuf + 3 * ibufsize / 4;
 	return (0);
 }