Index: sys/arch/arm/imx/imxuart.c
===================================================================
RCS file: /cvsroot/src/sys/arch/arm/imx/imxuart.c,v
retrieving revision 1.9
diff -u -r1.9 imxuart.c
--- sys/arch/arm/imx/imxuart.c	2 Feb 2012 19:42:58 -0000	1.9
+++ sys/arch/arm/imx/imxuart.c	27 Apr 2013 04:45:26 -0000
@@ -2372,6 +2372,8 @@
 imxucnpollc(dev_t dev, int on)
 {
 
+	imxuart_readahead_in = 0;
+	imxuart_readahead_out = 0;
 }
 
 #endif	/* IMXUARTCONSOLE */
Index: sys/arch/arm/s3c2xx0/sscom.c
===================================================================
RCS file: /cvsroot/src/sys/arch/arm/s3c2xx0/sscom.c,v
retrieving revision 1.38
diff -u -r1.38 sscom.c
--- sys/arch/arm/s3c2xx0/sscom.c	27 Oct 2012 17:17:40 -0000	1.38
+++ sys/arch/arm/s3c2xx0/sscom.c	27 Apr 2013 04:45:26 -0000
@@ -1977,6 +1977,7 @@
 sscomcnpollc(dev_t dev, int on)
 {
 
+	sscom_readaheadcount = 0;
 }
 
 #endif /* SSCOM0CONSOLE||SSCOM1CONSOLE */
Index: sys/arch/evbarm/dev/plcom.c
===================================================================
RCS file: /cvsroot/src/sys/arch/evbarm/dev/plcom.c,v
retrieving revision 1.44
diff -u -r1.44 plcom.c
--- sys/arch/evbarm/dev/plcom.c	3 Mar 2013 10:26:18 -0000	1.44
+++ sys/arch/evbarm/dev/plcom.c	27 Apr 2013 04:45:30 -0000
@@ -2450,6 +2450,7 @@
 plcomcnpollc(dev_t dev, int on)
 {
 
+	plcom_readaheadcount = 0;
 }
 
 #ifdef KGDB
Index: sys/dev/ic/com.c
===================================================================
RCS file: /cvsroot/src/sys/dev/ic/com.c,v
retrieving revision 1.308
diff -u -r1.308 com.c
--- sys/dev/ic/com.c	24 Feb 2013 06:21:36 -0000	1.308
+++ sys/dev/ic/com.c	27 Apr 2013 04:45:30 -0000
@@ -2308,6 +2308,7 @@
 comcnpollc(dev_t dev, int on)
 {
 
+	com_readaheadcount = 0;
 }
 
 #ifdef KGDB