netdev - [PATCH 21/24] make atomic_read() behave consistently on v850

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Date:	Thu, 9 Aug 2007 10:16:36 -0400
From:	Chris Snook <csnook@...hat.com>
To:	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
	torvalds@...ux-foundation.org
Cc:	netdev@...r.kernel.org, akpm@...ux-foundation.org, ak@...e.de,
	heiko.carstens@...ibm.com, davem@...emloft.net,
	schwidefsky@...ibm.com, wensong@...ux-vs.org, horms@...ge.net.au,
	wjiang@...ilience.com, cfriesen@...tel.com, zlynx@....org,
	rpjday@...dspring.com, jesper.juhl@...il.com
Subject: [PATCH 21/24] make atomic_read() behave consistently on v850

From: Chris Snook <csnook@...hat.com>

Make atomic_read() volatile on v850.  This ensures that busy-waiting
for an interrupt handler to change an atomic_t won't get compiled to an
infinite loop, consistent with SMP architectures.

Signed-off-by: Chris Snook <csnook@...hat.com>

--- linux-2.6.23-rc2-orig/include/asm-v850/atomic.h	2007-07-08 19:32:17.000000000 -0400
+++ linux-2.6.23-rc2/include/asm-v850/atomic.h	2007-08-09 07:50:15.000000000 -0400
@@ -27,7 +27,11 @@ typedef struct { int counter; } atomic_t
 
 #ifdef __KERNEL__
 
-#define atomic_read(v)		((v)->counter)
+/*
+ * Casting to volatile here minimizes the need for barriers,
+ * without having to declare the type itself as volatile.
+ */
+#define atomic_read(v)		(*(volatile int *)&(v)->counter)
 #define atomic_set(v,i)		(((v)->counter) = (i))
 
 static inline int atomic_add_return (int i, volatile atomic_t *v)
-
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