[PATCH] ARC: [BE] readl()/writel() to work in Big Endian CPU configuration

[Lada Trimasova]

read{l,w}() write{l,w}() primitives should use le{16,32}_to_cpu() and
cpu_to_le{16,32}() respectively to ensure device registers are read
correctly in Big Endian CPU configuration.

Per Arnd Bergmann
| Most drivers using readl() or readl_relaxed() expect those to perform byte
| swaps on big-endian architectures, as the registers tend to be fixed endian

This was needed for getting UART to work correctly on a Big Endian ARC.

The ARC accessors originally were fine, and the bug got introduced
inadventently by commit b8a033023994 ("ARCv2: barriers")

Fixes: b8a033023994 ("ARCv2: barriers")
Link: http://lkml.kernel.org/r/201603100845.30602.arnd@xxxxxxxx
Cc: Alexey Brodkin <abrodkin@xxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx  [4.2+]
Cc: Arnd Bergmann <arnd@xxxxxxxx>
Signed-off-by: Lada Trimasova <ltrimas@xxxxxxxxxxxx>
[vgupta: beefed up changelog, added Fixes/stable tags]
Signed-off-by: Vineet Gupta <vgupta@xxxxxxxxxxxx>
---
 arch/arc/include/asm/io.h | 18 +++++++++++++-----
 1 file changed, 13 insertions(+), 5 deletions(-)

diff --git a/arch/arc/include/asm/io.h b/arch/arc/include/asm/io.h
index 694ece8a0243..27b17adea50d 100644
--- a/arch/arc/include/asm/io.h
+++ b/arch/arc/include/asm/io.h
@@ -129,15 +129,23 @@ static inline void __raw_writel(u32 w, volatile void __iomem
*addr)
 #define writel(v,c)		({ __iowmb(); writel_relaxed(v,c); })

 /*
- * Relaxed API for drivers which can handle any ordering themselves
+ * Relaxed API for drivers which can handle barrier ordering themselves
+ *
+ * Also these are defined to perform little endian accesses.
+ * To provide the typical device register semantics of fixed endian,
+ * swap the byte order for Big Endian
+ *
+ * http://lkml.kernel.org/r/201603100845.30602.arnd@xxxxxxxx
  */
 #define readb_relaxed(c)	__raw_readb(c)
-#define readw_relaxed(c)	__raw_readw(c)
-#define readl_relaxed(c)	__raw_readl(c)
+#define readw_relaxed(c) ({ u16 __r = le16_to_cpu((__force __le16) \
+					__raw_readw(c)); __r; })
+#define readl_relaxed(c) ({ u32 __r = le32_to_cpu((__force __le32) \
+					__raw_readl(c)); __r; })

 #define writeb_relaxed(v,c)	__raw_writeb(v,c)
-#define writew_relaxed(v,c)	__raw_writew(v,c)
-#define writel_relaxed(v,c)	__raw_writel(v,c)
+#define writew_relaxed(v,c)	__raw_writew((__force u16) cpu_to_le16(v),c)
+#define writel_relaxed(v,c)	__raw_writel((__force u32) cpu_to_le32(v),c)

 #include <asm-generic/io.h>

-- 
2.5.0