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.palt...@synopsys.com>
---
arch/arc/include/asm/io.h | 31 ++++++++++++++++++++-----------
1 file changed, 20 insertions(+), 11 deletions(-)
diff --git a/arch/arc/include/asm/io.h b/arch/arc/include/asm/io.h
index 1f1ae889f3a..50c88456002 100644
--- a/arch/arc/include/asm/io.h
+++ b/arch/arc/include/asm/io.h
@@ -9,6 +9,13 @@
#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 +52,8 @@
#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 +65,18 @@ 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)
--
2.21.1
