Subject: port-i386/2299: Some Pee Cees need 16550 FIFOs turned off to detect properly from DOS
To: None <gnats-bugs@NetBSD.ORG>
From: None <>
List: netbsd-bugs
Date: 04/04/1996 00:42:02
>Number:         2299
>Category:       port-i386
>Synopsis:       Pee Cees suck, especially some of their BIOSes
>Confidential:   no
>Severity:       non-critical
>Priority:       medium
>Responsible:    gnats-admin (GNATS administrator)
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Thu Apr  4 01:05:01 1996
>Originator:     Ken Hornstein
>Release:        4/3/96 <NetBSD-current source date>
System: NetBSD excalibur 1.1B NetBSD 1.1B (EXCALIBUR) #17: Wed Apr 3 20:09:04 EST 1996 kenh@excalibur:/usr/src/sys/arch/i386/compile/EXCALIBUR i386

Certain PC BIOSes won't detect 16550 UARTs when the FIFO is enabled.  While
this doesn't affect NetBSD, it does present a problem when DOS is booted
after booting NetBSD.
Find a PC with a deficient BIOS, boot into NetBSD, then boot into DOS.
Notice that the BIOS doesn't detect com ports with 16550's.
Here's a patch that turns off the FIFO in the device close routine (I'm not
sure if this is a better solution than a shutdown hook).

--- com.c.orig	Wed Apr  3 20:01:59 1996
+++ com.c	Wed Apr  3 20:08:17 1996
@@ -654,6 +654,14 @@
 	CLR(tp->t_state, TS_BUSY | TS_FLUSH);
 	if (--comsopen == 0)
 		untimeout(compoll, NULL);
+	if (ISSET(sc->sc_hwflags, COM_HW_FIFO))
+		/*
+		 * Disable the FIFO upon close, as some buggy PC BIOSes
+		 * won't detect the UART otherwise
+		 */
+		bus_io_write_1(bc, ioh, com_fifo, 0);
 #ifdef notyet /* XXXX */
Too many ('s.