ARC: IO: add compiler barriers to IO accessors

We must use compiler barriers in C-version read/write IO accessors
before and after operation (read or write) so it won't be reordered
by compiler.

Fixes commit 07906b3dad15 ("ARC: Switch to generic accessors")

Signed-off-by: Eugeniy Paltsev <Eugeniy.Paltsev@synopsys.com>
Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>

diff --git a/arch/arc/include/asm/io.h b/arch/arc/include/asm/io.h
index 1f1ae889f3a4e86fbd828ab8008ecb6c806bd0d0..a4171a3e5cca65244c72c671105667e065a99558 100644 (file)
--- a/arch/arc/include/asm/io.h
+++ b/arch/arc/include/asm/io.h
@@ -9,6 +9,12 @@
 #include <linux/types.h>
 #include <asm/byteorder.h>
 
+/*
+ * Compiler barrier. It prevents compiler from reordering instructions before
+ * and after it. It doesn't prevent HW (CPU) from any reordering though.
+ */
+#define __comp_b()             asm volatile("" : : : "memory")
+
 #ifdef __ARCHS__
 
 /*
@@ -45,8 +51,8 @@
 #define __iormb()              rmb()
 #define __iowmb()              wmb()
 #else
-#define __iormb()              asm volatile("" : : : "memory")
-#define __iowmb()              asm volatile("" : : : "memory")
+#define __iormb()              __comp_b()
+#define __iowmb()              __comp_b()
 #endif
 
 static inline void sync(void)
@@ -58,16 +64,18 @@ static inline void sync(void)
  * We must use 'volatile' in C-version read/write IO accessors implementation
  * to avoid merging several reads (writes) into one read (write), or optimizing
  * them out by compiler.
+ * We must use compiler barriers before and after operation (read or write) so
+ * it won't be reordered by compiler.
  */
-#define __arch_getb(a)         (*(volatile u8 *)(a))
-#define __arch_getw(a)         (*(volatile u16 *)(a))
-#define __arch_getl(a)         (*(volatile u32 *)(a))
-#define __arch_getq(a)         (*(volatile u64 *)(a))
-
-#define __arch_putb(v, a)      (*(volatile u8 *)(a) = (v))
-#define __arch_putw(v, a)      (*(volatile u16 *)(a) = (v))
-#define __arch_putl(v, a)      (*(volatile u32 *)(a) = (v))
-#define __arch_putq(v, a)      (*(volatile u64 *)(a) = (v))
+#define __arch_getb(a)         ({ u8  __v; __comp_b(); __v = *(volatile u8  *)(a); __comp_b(); __v; })
+#define __arch_getw(a)         ({ u16 __v; __comp_b(); __v = *(volatile u16 *)(a); __comp_b(); __v; })
+#define __arch_getl(a)         ({ u32 __v; __comp_b(); __v = *(volatile u32 *)(a); __comp_b(); __v; })
+#define __arch_getq(a)         ({ u64 __v; __comp_b(); __v = *(volatile u64 *)(a); __comp_b(); __v; })
+
+#define __arch_putb(v, a)      ({ __comp_b(); *(volatile u8  *)(a) = (v); __comp_b(); })
+#define __arch_putw(v, a)      ({ __comp_b(); *(volatile u16 *)(a) = (v); __comp_b(); })
+#define __arch_putl(v, a)      ({ __comp_b(); *(volatile u32 *)(a) = (v); __comp_b(); })
+#define __arch_putq(v, a)      ({ __comp_b(); *(volatile u64 *)(a) = (v); __comp_b(); })
 
 
 #define __raw_writeb(v, a)     __arch_putb(v, a)