[src/trunk]: src/sys/arch/evbarm/dev Don't busy wait for a character in plcom...

[skrll <skrll%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/1fb11d9de60e
branches:  trunk
changeset: 462022:1fb11d9de60e
user:      skrll <skrll%NetBSD.org@localhost>
date:      Tue Jul 23 12:13:47 2019 +0000

description:
Don't busy wait for a character in plcom_common_getc, but instead
return -1 if there are no characters available.

Fixes WSDISPLAY_MULTICONS for RaspberryPI and GENERIC.

Thanks to jmcneill@ for the hint

diffstat:

 sys/arch/evbarm/dev/plcom.c |  13 +++++++------
 1 files changed, 7 insertions(+), 6 deletions(-)

diffs (41 lines):

diff -r f77907c8babc -r 1fb11d9de60e sys/arch/evbarm/dev/plcom.c
--- a/sys/arch/evbarm/dev/plcom.c       Tue Jul 23 12:10:38 2019 +0000
+++ b/sys/arch/evbarm/dev/plcom.c       Tue Jul 23 12:13:47 2019 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: plcom.c,v 1.57 2019/07/23 12:10:38 skrll Exp $ */
+/*     $NetBSD: plcom.c,v 1.58 2019/07/23 12:13:47 skrll Exp $ */
 
 /*-
  * Copyright (c) 2001 ARM Ltd
@@ -94,7 +94,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: plcom.c,v 1.57 2019/07/23 12:10:38 skrll Exp $");
+__KERNEL_RCSID(0, "$NetBSD: plcom.c,v 1.58 2019/07/23 12:13:47 skrll Exp $");
 
 #include "opt_plcom.h"
 #include "opt_ddb.h"
@@ -2275,7 +2275,7 @@
 plcom_common_getc(dev_t dev, struct plcom_instance *pi)
 {
        int s = splserial();
-       u_char stat, c;
+       u_char c;
 
        /* got a character from reading things earlier */
        if (plcom_readaheadcount > 0) {
@@ -2290,9 +2290,10 @@
                return c;
        }
 
-       /* block until a character becomes available */
-       while (ISSET(stat = PREAD1(pi, PL01XCOM_FR), PL01X_FR_RXFE))
-               ;
+       if (ISSET(PREAD1(pi, PL01XCOM_FR), PL01X_FR_RXFE)) {
+               splx(s);
+               return -1;
+       }
 
        c = PREAD1(pi, PL01XCOM_DR);
        {