[PATCH 1/2 v3] alpha: add a delay to inb_p, inb_w and inb_l

[Mikulas Patocka <mpatocka@redhat.com>]

alpha: add a delay to inb_p, inb_w and inb_l

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. Note that we don't have to add a delay before
outb_p, outw_p and outl_p, because there is already a "mb()" instruction
before them and this instruction slows down access sufficiently.

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