From: Mikulas Patocka <mpatocka@redhat.com>
To: Richard Henderson <rth@twiddle.net>,
Ivan Kokshaysky <ink@jurassic.park.msu.ru>,
Matt Turner <mattst88@gmail.com>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: linux-alpha@vger.kernel.org, Sinan Kaya <okaya@codeaurora.org>,
Arnd Bergmann <arnd@arndb.de>,
linux-serial@vger.kernel.org, linux-rtc@vger.kernel.org
Subject: [PATCH 2/2] alpha: add a delay before serial port read
Date: Wed, 6 May 2020 07:23:31 -0400 (EDT) [thread overview]
Message-ID: <alpine.LRH.2.02.2005060721450.25338@file01.intranet.prod.int.rdu2.redhat.com> (raw)
The patch 92d7223a74235054f2aa7227d207d9c57f84dca0 ("alpha: io: reorder
barriers to guarantee writeX() and iowriteX() ordering #2") broke boot on
the Alpha Avanti platform.
The patch changes timing between accesses to the ISA bus, in particular,
it reduces the time between "write" access and a subsequent "read" access.
This causes lock-up when accessing the real time clock and serial ports.
This patch fixes the serial ports by adding a small delay before the "inb"
instruction.
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Fixes: 92d7223a7423 ("alpha: io: reorder barriers to guarantee writeX() and iowriteX() ordering #2")
Cc: stable@vger.kernel.org # v4.17+
---
drivers/tty/serial/8250/8250_port.c | 4 ++++
1 file changed, 4 insertions(+)
Index: linux-stable/drivers/tty/serial/8250/8250_port.c
===================================================================
--- linux-stable.orig/drivers/tty/serial/8250/8250_port.c 2020-05-06 08:25:19.000000000 +0200
+++ linux-stable/drivers/tty/serial/8250/8250_port.c 2020-05-06 09:04:17.000000000 +0200
@@ -442,6 +442,10 @@ static unsigned int mem32be_serial_in(st
static unsigned int io_serial_in(struct uart_port *p, int offset)
{
+#ifdef CONFIG_ALPHA
+/* we need a small delay, the Alpha Avanti chipset locks up with back-to-back accesses */
+ ndelay(300);
+#endif
offset = offset << p->regshift;
return inb(p->iobase + offset);
}
next reply other threads:[~2020-05-06 11:23 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-06 11:23 Mikulas Patocka [this message]
2020-05-06 11:47 ` [PATCH 2/2] alpha: add a delay before serial port read Greg Kroah-Hartman
2020-05-06 15:29 ` [PATCH 2/2 v2] " Mikulas Patocka
2020-05-06 15:49 ` Greg Kroah-Hartman
2020-05-06 15:57 ` Mikulas Patocka
2020-05-06 16:08 ` Greg Kroah-Hartman
2020-05-06 17:04 ` [PATCH 2/2 v3] " Mikulas Patocka
2020-05-06 17:45 ` Greg Kroah-Hartman
2020-05-07 8:18 ` [PATCH 2/2 v4] " Mikulas Patocka
2020-05-07 8:52 ` Greg Kroah-Hartman
2020-05-07 10:53 ` Mikulas Patocka
2020-05-07 11:10 ` Greg Kroah-Hartman
2020-05-07 12:53 ` Mikulas Patocka
2020-05-07 12:57 ` [PATCH 2/2 v5] " Mikulas Patocka
2020-05-07 13:58 ` Greg Kroah-Hartman
2020-05-07 14:03 ` Mikulas Patocka
2020-05-10 0:13 ` [PATCH 2/2 v4] " Maciej W. Rozycki
2020-05-23 10:37 ` Mikulas Patocka
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