Patch "ARC: [BE] readl()/writel() to work in Big Endian CPU configuration" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

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

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
arc-readl-writel-to-work-in-big-endian-cpu-configuration.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Lada Trimasova <[email protected]>
Date: Wed, 9 Mar 2016 20:21:04 +0300
Subject: ARC: [BE] readl()/writel() to work in Big Endian CPU configuration

From: Lada Trimasova <[email protected]>

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")

---
 arch/arc/include/asm/io.h |   18 +++++++++++++-----
 1 file changed, 13 insertions(+), 5 deletions(-)

@@ -129,15 +129,23 @@ static inline void __raw_writel(u32 w, v
 #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/[email protected]
  */
 #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>
 

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/arc-readl-writel-to-work-in-big-endian-cpu-configuration.patch