On Wed, 6 May 2020, Mikulas Patocka wrote:

On Wed, 6 May 2020, Arnd Bergmann wrote:

quoted

On Wed, May 6, 2020 at 1:21 PM Mikulas Patocka [off-list ref] wrote:

quoted

 /*
  * 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)); \

The inb_p() / outb_p() functions are meant to already have a delay in them,
maybe we should just add it there for alpha?

     Arnd

Yes, that is possible too - it fixes the real time clock hang for me.


-#define inb_p		inb
-#define inw_p		inw
-#define inl_p		inl
+#define inb_p(x)	(ndelay(300), inb(x))
+#define inw_p(x)	(ndelay(300), inw(x))
+#define inl_p(x)	(ndelay(300), inl(x))
 #define outb_p		outb
 #define outw_p		outw
 #define outl_p		outl

300ns was too low. We need at least 1400ns to fix the hang reliably.

Mikulas


From: Mikulas Patocka <mpatocka@redhat.com>

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 to the inb_p,
inw_p and inl_p macros.

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/io.h |    7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

Index: linux-stable/arch/alpha/include/asm/io.h
===================================================================

--- linux-stable.orig/arch/alpha/include/asm/io.h	2020-05-07 09:54:52.000000000 +0200
+++ linux-stable/arch/alpha/include/asm/io.h	2020-05-07 09:54:52.000000000 +0200

@@ -6,6 +6,7 @@
 
 #include <linux/kernel.h>
 #include <linux/mm.h>
+#include <linux/delay.h>
 #include <asm/compiler.h>
 #include <asm/pgtable.h>
 #include <asm/machvec.h>

@@ -481,9 +482,9 @@ extern inline void writeq(u64 b, volatil
 #define iowrite16be(v,p) iowrite16(cpu_to_be16(v), (p))
 #define iowrite32be(v,p) iowrite32(cpu_to_be32(v), (p))
 
-#define inb_p		inb
-#define inw_p		inw
-#define inl_p		inl
+#define inb_p(x)	(ndelay(1400), inb(x))
+#define inw_p(x)	(ndelay(1400), inw(x))
+#define inl_p(x)	(ndelay(1400), inl(x))
 #define outb_p		outb
 #define outw_p		outw
 #define outl_p		outl