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* [PATCH 1/2] alpha: add a delay between RTC port write and read
@ 2020-05-06 11:21 Mikulas Patocka
  2020-05-06 14:20 ` Arnd Bergmann
  0 siblings, 1 reply; 45+ messages in thread
From: Mikulas Patocka @ 2020-05-06 11:21 UTC (permalink / raw)
  To: Richard Henderson, Ivan Kokshaysky, Matt Turner, Greg Kroah-Hartman
  Cc: linux-alpha, Sinan Kaya, Arnd Bergmann, linux-serial, linux-rtc

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 real time clock by adding a small delay between
outb_p and inb_p.

Note that we don't have to add the delay to CMOS_WRITE, because it
consists of two write accesses and they already have mb() between them.

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+

---
 arch/alpha/include/asm/mc146818rtc.h |    4 ++++
 1 file changed, 4 insertions(+)

Index: linux-stable/arch/alpha/include/asm/mc146818rtc.h
===================================================================
--- linux-stable.orig/arch/alpha/include/asm/mc146818rtc.h	2020-05-05 20:48:30.000000000 +0200
+++ linux-stable/arch/alpha/include/asm/mc146818rtc.h	2020-05-05 21:05:53.000000000 +0200
@@ -15,9 +15,13 @@
 /*
  * The yet supported machines all access the RTC index register via
  * an ISA port access but the way to access the date register differs ...
+ *
+ * The ISA bus on Alpha Avanti doesn't like back-to-back accesses,
+ * we need to add a small delay.
  */
 #define CMOS_READ(addr) ({ \
 outb_p((addr),RTC_PORT(0)); \
+udelay(2); \
 inb_p(RTC_PORT(1)); \
 })
 #define CMOS_WRITE(val, addr) ({ \


^ permalink raw reply	[flat|nested] 45+ messages in thread

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Thread overview: 45+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2020-05-06 11:21 [PATCH 1/2] alpha: add a delay between RTC port write and read Mikulas Patocka
2020-05-06 14:20 ` Arnd Bergmann
2020-05-06 17:12   ` [PATCH 1/2 v2] alpha: add a delay to inb_p, inb_w and inb_l Mikulas Patocka
2020-05-07  8:06     ` [PATCH 1/2 v3] " Mikulas Patocka
2020-05-07  8:20       ` Greg Kroah-Hartman
2020-05-07 10:53         ` Mikulas Patocka
2020-05-07 13:30       ` Arnd Bergmann
2020-05-07 14:09         ` Mikulas Patocka
2020-05-07 15:08           ` Arnd Bergmann
2020-05-07 15:45             ` Mikulas Patocka
2020-05-07 15:46             ` [PATCH v4] alpha: add a barrier after outb, outw and outl Mikulas Patocka
2020-05-07 19:12               ` Arnd Bergmann
2020-05-10  1:27                 ` Maciej W. Rozycki
2020-05-10  1:25             ` [PATCH 1/2 v3] alpha: add a delay to inb_p, inb_w and inb_l Maciej W. Rozycki
2020-05-10 18:50               ` Mikulas Patocka
2020-05-11 14:58                 ` Maciej W. Rozycki
2020-05-12 19:35                   ` Mikulas Patocka
2020-05-13 14:41                   ` Ivan Kokshaysky
2020-05-13 16:13                     ` Greg Kroah-Hartman
2020-05-13 17:17                     ` Maciej W. Rozycki
2020-05-22 13:03                       ` Mikulas Patocka
2020-05-22 13:37                         ` Maciej W. Rozycki
2020-05-22 13:26                     ` Mikulas Patocka
2020-05-22 20:00                       ` Mikulas Patocka
2020-05-23 10:26                         ` [PATCH v4] alpha: fix memory barriers so that they conform to the specification Mikulas Patocka
2020-05-23 15:10                           ` Ivan Kokshaysky
2020-05-23 15:34                             ` Mikulas Patocka
2020-05-23 15:37                               ` [PATCH v5] " Mikulas Patocka
2020-05-24 14:54                                 ` Maciej W. Rozycki
2020-05-25 13:56                                   ` Mikulas Patocka
2020-05-25 14:07                                     ` Arnd Bergmann
2020-05-25 14:45                                     ` Maciej W. Rozycki
2020-05-25 15:53                                       ` [PATCH v6] " Mikulas Patocka
2020-05-26 14:47                                         ` [PATCH v7] " Mikulas Patocka
2020-05-27  0:18                                           ` Maciej W. Rozycki
2020-06-08  6:58                                             ` Mikulas Patocka
2020-06-08 23:49                                               ` Matt Turner
2020-05-25 15:54                                       ` [PATCH v5] " Mikulas Patocka
2020-05-25 16:39                                         ` Maciej W. Rozycki
2020-05-26 14:48                                           ` Mikulas Patocka
2020-05-27  0:23                                             ` Maciej W. Rozycki
2020-05-23 16:44                               ` [PATCH v4] " Maciej W. Rozycki
2020-05-23 17:09                                 ` Mikulas Patocka
2020-05-23 19:27                                   ` Maciej W. Rozycki
2020-05-23 20:11                                     ` Mikulas Patocka

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