[PATCH 4.2.y-ckt 106/218] ARC: [BE] readl()/writel() to work in Big Endian CPU configuration

From: Kamal Mostafa
Date: Thu Mar 31 2016 - 16:58:05 EST

4.2.8-ckt7 -stable review patch. If anyone has any objections, please let me know.


From: Lada Trimasova <ltrimas@xxxxxxxxxxxx>

commit f778cc65717687a3d3f26dd21bef62cd059f1b8b upstream.

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: 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>
Signed-off-by: Kamal Mostafa <kamal@xxxxxxxxxxxxx>
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 694ece8..27b17ad 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>