From 92d0aa20dcc915dc4111e8554d69219f1876e5dc Mon Sep 17 00:00:00 2001
From: Bruce Evans <bde@FreeBSD.org>
Date: Mon, 30 Sep 1996 12:22:27 +0000
Subject: [PATCH] Work around UMC8669F and Startech UART bugs by not writing to
 the divisor latch registers if the registers wouldn't change.

Use the default console cfcr setting while setting the divisor
latch registers for console i/o.  Input may be messed up by
transiently changing the cfcr.

Use a usual cfcr setting while setting the divisor latch registers
in the probe.  This shouldn't matter, but this is not the place to
test the UART's handling of 5 bit words.

Removed a stale devfs comment.
---
 sys/dev/sio/sio.c  | 47 +++++++++++++++++++++++++++++++++++-----------
 sys/i386/isa/sio.c | 47 +++++++++++++++++++++++++++++++++++-----------
 sys/isa/sio.c      | 47 +++++++++++++++++++++++++++++++++++-----------
 3 files changed, 108 insertions(+), 33 deletions(-)

diff --git a/sys/dev/sio/sio.c b/sys/dev/sio/sio.c
index 8976cae1ace1..4b4f39d49eb6 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 1.145 1996/09/06 23:08:05 phk Exp $
+ *	$Id: sio.c,v 1.146 1996/09/14 04:27:42 bde Exp $
  */
 
 #include "opt_comconsole.h"
@@ -569,7 +569,7 @@ sioprobe(dev)
 	 * XXX what about the UART bug avoided by waiting in comparam()?
 	 * We don't want to to wait long enough to drain at 2 bps.
 	 */
-	outb(iobase + com_cfcr, CFCR_DLAB);
+	outb(iobase + com_cfcr, CFCR_DLAB | CFCR_8BITS);
 	outb(iobase + com_dlbl, COMBRD(9600) & 0xff);
 	outb(iobase + com_dlbh, (u_int) COMBRD(9600) >> 8);
 	outb(iobase + com_cfcr, CFCR_8BITS);
@@ -942,7 +942,6 @@ determined_type: ;
 	dev = makedev(CDEV_MAJOR, 0);
 	cdevsw_add(&dev, &sio_cdevsw, NULL);
 #ifdef DEVFS
-		/* devsw, minor, type, uid, gid, perm, fmt, ... */
 	com->devfs_token_ttyd = devfs_add_devswf(&sio_cdevsw,
 		unit, DV_CHR,
 		UID_ROOT, GID_WHEEL, 0600, "ttyd%n", unit);
@@ -1826,6 +1825,8 @@ comparam(tp, t)
 	int		cflag;
 	struct com_s	*com;
 	int		divisor;
+	u_char		dlbh;
+	u_char		dlbl;
 	int		error;
 	Port_t		iobase;
 	int		s;
@@ -1937,8 +1938,18 @@ retry:
 
 	if (divisor != 0) {
 		outb(iobase + com_cfcr, cfcr | CFCR_DLAB);
-		outb(iobase + com_dlbl, divisor & 0xFF);
-		outb(iobase + com_dlbh, (u_int) divisor >> 8);
+		/*
+		 * Only set the divisor registers if they would change,
+		 * since on some 16550 incompatibles (UMC8669F), setting
+		 * them while input is arriving them loses sync until
+		 * data stops arriving.
+		 */
+		dlbl = divisor & 0xFF;
+		if (inb(iobase + com_dlbl) != dlbl)
+			outb(iobase + com_dlbl, dlbl);
+		dlbh = (u_int) divisor >> 8;
+		if (inb(iobase + com_dlbh) != dlbh)
+			outb(iobase + com_dlbh, dlbh);
 	}
 	outb(iobase + com_cfcr, com->cfcr_image = cfcr);
 	if (!(tp->t_state & TS_TTSTOP))
@@ -2322,6 +2333,8 @@ siocnopen(sp)
 	struct siocnstate	*sp;
 {
 	int	divisor;
+	u_char	dlbh;
+	u_char	dlbl;
 	Port_t	iobase;
 
 	/*
@@ -2334,12 +2347,22 @@ siocnopen(sp)
 	outb(iobase + com_ier, 0);	/* spltty() doesn't stop siointr() */
 	siocntxwait();
 	sp->cfcr = inb(iobase + com_cfcr);
-	outb(iobase + com_cfcr, CFCR_DLAB);
+	outb(iobase + com_cfcr, CFCR_DLAB | CFCR_8BITS);
 	sp->dlbl = inb(iobase + com_dlbl);
 	sp->dlbh = inb(iobase + com_dlbh);
+	/*
+	 * Only set the divisor registers if they would change, since on
+	 * some 16550 incompatibles (Startech), setting them clears the
+	 * data input register.  This also reduces the effects of the
+	 * UMC8669F bug.
+	 */
 	divisor = ttspeedtab(comdefaultrate, comspeedtab);
-	outb(iobase + com_dlbl, divisor & 0xFF);
-	outb(iobase + com_dlbh, (u_int) divisor >> 8);
+	dlbl = divisor & 0xFF;
+	if (sp->dlbl != dlbl)
+		outb(iobase + com_dlbl, dlbl);
+	dlbh = (u_int) divisor >> 8;
+	if (sp->dlbh != dlbh)
+		outb(iobase + com_dlbh, dlbh);
 	outb(iobase + com_cfcr, CFCR_8BITS);
 	sp->mcr = inb(iobase + com_mcr);
 	/*
@@ -2361,9 +2384,11 @@ siocnclose(sp)
 	 */
 	siocntxwait();
 	iobase = siocniobase;
-	outb(iobase + com_cfcr, CFCR_DLAB);
-	outb(iobase + com_dlbl, sp->dlbl);
-	outb(iobase + com_dlbh, sp->dlbh);
+	outb(iobase + com_cfcr, CFCR_DLAB | CFCR_8BITS);
+	if (sp->dlbl != inb(iobase + com_dlbl))
+		outb(iobase + com_dlbl, sp->dlbl);
+	if (sp->dlbh != inb(iobase + com_dlbh))
+		outb(iobase + com_dlbh, sp->dlbh);
 	outb(iobase + com_cfcr, sp->cfcr);
 	/*
 	 * XXX damp oscillations of MCR_DTR and MCR_RTS by not restoring them.
diff --git a/sys/i386/isa/sio.c b/sys/i386/isa/sio.c
index 8976cae1ace1..4b4f39d49eb6 100644
--- a/sys/i386/isa/sio.c
+++ b/sys/i386/isa/sio.c
@@ -31,7 +31,7 @@
  * SUCH DAMAGE.
  *
  *	from: @(#)com.c	7.5 (Berkeley) 5/16/91
- *	$Id: sio.c,v 1.145 1996/09/06 23:08:05 phk Exp $
+ *	$Id: sio.c,v 1.146 1996/09/14 04:27:42 bde Exp $
  */
 
 #include "opt_comconsole.h"
@@ -569,7 +569,7 @@ sioprobe(dev)
 	 * XXX what about the UART bug avoided by waiting in comparam()?
 	 * We don't want to to wait long enough to drain at 2 bps.
 	 */
-	outb(iobase + com_cfcr, CFCR_DLAB);
+	outb(iobase + com_cfcr, CFCR_DLAB | CFCR_8BITS);
 	outb(iobase + com_dlbl, COMBRD(9600) & 0xff);
 	outb(iobase + com_dlbh, (u_int) COMBRD(9600) >> 8);
 	outb(iobase + com_cfcr, CFCR_8BITS);
@@ -942,7 +942,6 @@ determined_type: ;
 	dev = makedev(CDEV_MAJOR, 0);
 	cdevsw_add(&dev, &sio_cdevsw, NULL);
 #ifdef DEVFS
-		/* devsw, minor, type, uid, gid, perm, fmt, ... */
 	com->devfs_token_ttyd = devfs_add_devswf(&sio_cdevsw,
 		unit, DV_CHR,
 		UID_ROOT, GID_WHEEL, 0600, "ttyd%n", unit);
@@ -1826,6 +1825,8 @@ comparam(tp, t)
 	int		cflag;
 	struct com_s	*com;
 	int		divisor;
+	u_char		dlbh;
+	u_char		dlbl;
 	int		error;
 	Port_t		iobase;
 	int		s;
@@ -1937,8 +1938,18 @@ retry:
 
 	if (divisor != 0) {
 		outb(iobase + com_cfcr, cfcr | CFCR_DLAB);
-		outb(iobase + com_dlbl, divisor & 0xFF);
-		outb(iobase + com_dlbh, (u_int) divisor >> 8);
+		/*
+		 * Only set the divisor registers if they would change,
+		 * since on some 16550 incompatibles (UMC8669F), setting
+		 * them while input is arriving them loses sync until
+		 * data stops arriving.
+		 */
+		dlbl = divisor & 0xFF;
+		if (inb(iobase + com_dlbl) != dlbl)
+			outb(iobase + com_dlbl, dlbl);
+		dlbh = (u_int) divisor >> 8;
+		if (inb(iobase + com_dlbh) != dlbh)
+			outb(iobase + com_dlbh, dlbh);
 	}
 	outb(iobase + com_cfcr, com->cfcr_image = cfcr);
 	if (!(tp->t_state & TS_TTSTOP))
@@ -2322,6 +2333,8 @@ siocnopen(sp)
 	struct siocnstate	*sp;
 {
 	int	divisor;
+	u_char	dlbh;
+	u_char	dlbl;
 	Port_t	iobase;
 
 	/*
@@ -2334,12 +2347,22 @@ siocnopen(sp)
 	outb(iobase + com_ier, 0);	/* spltty() doesn't stop siointr() */
 	siocntxwait();
 	sp->cfcr = inb(iobase + com_cfcr);
-	outb(iobase + com_cfcr, CFCR_DLAB);
+	outb(iobase + com_cfcr, CFCR_DLAB | CFCR_8BITS);
 	sp->dlbl = inb(iobase + com_dlbl);
 	sp->dlbh = inb(iobase + com_dlbh);
+	/*
+	 * Only set the divisor registers if they would change, since on
+	 * some 16550 incompatibles (Startech), setting them clears the
+	 * data input register.  This also reduces the effects of the
+	 * UMC8669F bug.
+	 */
 	divisor = ttspeedtab(comdefaultrate, comspeedtab);
-	outb(iobase + com_dlbl, divisor & 0xFF);
-	outb(iobase + com_dlbh, (u_int) divisor >> 8);
+	dlbl = divisor & 0xFF;
+	if (sp->dlbl != dlbl)
+		outb(iobase + com_dlbl, dlbl);
+	dlbh = (u_int) divisor >> 8;
+	if (sp->dlbh != dlbh)
+		outb(iobase + com_dlbh, dlbh);
 	outb(iobase + com_cfcr, CFCR_8BITS);
 	sp->mcr = inb(iobase + com_mcr);
 	/*
@@ -2361,9 +2384,11 @@ siocnclose(sp)
 	 */
 	siocntxwait();
 	iobase = siocniobase;
-	outb(iobase + com_cfcr, CFCR_DLAB);
-	outb(iobase + com_dlbl, sp->dlbl);
-	outb(iobase + com_dlbh, sp->dlbh);
+	outb(iobase + com_cfcr, CFCR_DLAB | CFCR_8BITS);
+	if (sp->dlbl != inb(iobase + com_dlbl))
+		outb(iobase + com_dlbl, sp->dlbl);
+	if (sp->dlbh != inb(iobase + com_dlbh))
+		outb(iobase + com_dlbh, sp->dlbh);
 	outb(iobase + com_cfcr, sp->cfcr);
 	/*
 	 * XXX damp oscillations of MCR_DTR and MCR_RTS by not restoring them.
diff --git a/sys/isa/sio.c b/sys/isa/sio.c
index 8976cae1ace1..4b4f39d49eb6 100644
--- a/sys/isa/sio.c
+++ b/sys/isa/sio.c
@@ -31,7 +31,7 @@
  * SUCH DAMAGE.
  *
  *	from: @(#)com.c	7.5 (Berkeley) 5/16/91
- *	$Id: sio.c,v 1.145 1996/09/06 23:08:05 phk Exp $
+ *	$Id: sio.c,v 1.146 1996/09/14 04:27:42 bde Exp $
  */
 
 #include "opt_comconsole.h"
@@ -569,7 +569,7 @@ sioprobe(dev)
 	 * XXX what about the UART bug avoided by waiting in comparam()?
 	 * We don't want to to wait long enough to drain at 2 bps.
 	 */
-	outb(iobase + com_cfcr, CFCR_DLAB);
+	outb(iobase + com_cfcr, CFCR_DLAB | CFCR_8BITS);
 	outb(iobase + com_dlbl, COMBRD(9600) & 0xff);
 	outb(iobase + com_dlbh, (u_int) COMBRD(9600) >> 8);
 	outb(iobase + com_cfcr, CFCR_8BITS);
@@ -942,7 +942,6 @@ determined_type: ;
 	dev = makedev(CDEV_MAJOR, 0);
 	cdevsw_add(&dev, &sio_cdevsw, NULL);
 #ifdef DEVFS
-		/* devsw, minor, type, uid, gid, perm, fmt, ... */
 	com->devfs_token_ttyd = devfs_add_devswf(&sio_cdevsw,
 		unit, DV_CHR,
 		UID_ROOT, GID_WHEEL, 0600, "ttyd%n", unit);
@@ -1826,6 +1825,8 @@ comparam(tp, t)
 	int		cflag;
 	struct com_s	*com;
 	int		divisor;
+	u_char		dlbh;
+	u_char		dlbl;
 	int		error;
 	Port_t		iobase;
 	int		s;
@@ -1937,8 +1938,18 @@ retry:
 
 	if (divisor != 0) {
 		outb(iobase + com_cfcr, cfcr | CFCR_DLAB);
-		outb(iobase + com_dlbl, divisor & 0xFF);
-		outb(iobase + com_dlbh, (u_int) divisor >> 8);
+		/*
+		 * Only set the divisor registers if they would change,
+		 * since on some 16550 incompatibles (UMC8669F), setting
+		 * them while input is arriving them loses sync until
+		 * data stops arriving.
+		 */
+		dlbl = divisor & 0xFF;
+		if (inb(iobase + com_dlbl) != dlbl)
+			outb(iobase + com_dlbl, dlbl);
+		dlbh = (u_int) divisor >> 8;
+		if (inb(iobase + com_dlbh) != dlbh)
+			outb(iobase + com_dlbh, dlbh);
 	}
 	outb(iobase + com_cfcr, com->cfcr_image = cfcr);
 	if (!(tp->t_state & TS_TTSTOP))
@@ -2322,6 +2333,8 @@ siocnopen(sp)
 	struct siocnstate	*sp;
 {
 	int	divisor;
+	u_char	dlbh;
+	u_char	dlbl;
 	Port_t	iobase;
 
 	/*
@@ -2334,12 +2347,22 @@ siocnopen(sp)
 	outb(iobase + com_ier, 0);	/* spltty() doesn't stop siointr() */
 	siocntxwait();
 	sp->cfcr = inb(iobase + com_cfcr);
-	outb(iobase + com_cfcr, CFCR_DLAB);
+	outb(iobase + com_cfcr, CFCR_DLAB | CFCR_8BITS);
 	sp->dlbl = inb(iobase + com_dlbl);
 	sp->dlbh = inb(iobase + com_dlbh);
+	/*
+	 * Only set the divisor registers if they would change, since on
+	 * some 16550 incompatibles (Startech), setting them clears the
+	 * data input register.  This also reduces the effects of the
+	 * UMC8669F bug.
+	 */
 	divisor = ttspeedtab(comdefaultrate, comspeedtab);
-	outb(iobase + com_dlbl, divisor & 0xFF);
-	outb(iobase + com_dlbh, (u_int) divisor >> 8);
+	dlbl = divisor & 0xFF;
+	if (sp->dlbl != dlbl)
+		outb(iobase + com_dlbl, dlbl);
+	dlbh = (u_int) divisor >> 8;
+	if (sp->dlbh != dlbh)
+		outb(iobase + com_dlbh, dlbh);
 	outb(iobase + com_cfcr, CFCR_8BITS);
 	sp->mcr = inb(iobase + com_mcr);
 	/*
@@ -2361,9 +2384,11 @@ siocnclose(sp)
 	 */
 	siocntxwait();
 	iobase = siocniobase;
-	outb(iobase + com_cfcr, CFCR_DLAB);
-	outb(iobase + com_dlbl, sp->dlbl);
-	outb(iobase + com_dlbh, sp->dlbh);
+	outb(iobase + com_cfcr, CFCR_DLAB | CFCR_8BITS);
+	if (sp->dlbl != inb(iobase + com_dlbl))
+		outb(iobase + com_dlbl, sp->dlbl);
+	if (sp->dlbh != inb(iobase + com_dlbh))
+		outb(iobase + com_dlbh, sp->dlbh);
 	outb(iobase + com_cfcr, sp->cfcr);
 	/*
 	 * XXX damp oscillations of MCR_DTR and MCR_RTS by not restoring them.