linux-kernel - [PATCH v3 2/5] io: define stronger ordering for the default readX() implementation

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Date:   Wed,  4 Apr 2018 19:58:17 -0400
From:   Sinan Kaya <okaya@...eaurora.org>
To:     arnd@...db.de, timur@...eaurora.org, sulrich@...eaurora.org
Cc:     linux-arm-msm@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        Sinan Kaya <okaya@...eaurora.org>, linux-arch@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH v3 2/5] io: define stronger ordering for the default readX() implementation

The default implementation of mapping readX() to __raw_readX() is wrong.
readX() has stronger ordering semantics. Compiler is allowed to reorder
__raw_readX() against the memory accesses following register read.

Use the previously defined __io_ar() and __io_br() macros to harden
code generation according to architecture support.

Signed-off-by: Sinan Kaya <okaya@...eaurora.org>
---
 include/asm-generic/io.h | 28 ++++++++++++++++++++++++----
 1 file changed, 24 insertions(+), 4 deletions(-)

diff --git a/include/asm-generic/io.h b/include/asm-generic/io.h
index a3d349e..fc554af 100644
--- a/include/asm-generic/io.h
+++ b/include/asm-generic/io.h
@@ -153,7 +153,12 @@ static inline void __raw_writeq(u64 value, volatile void __iomem *addr)
 #define readb readb
 static inline u8 readb(const volatile void __iomem *addr)
 {
-	return __raw_readb(addr);
+	u8 val;
+
+	__io_br();
+	val = __raw_readb(addr);
+	__io_ar();
+	return val;
 }
 #endif
 
@@ -161,7 +166,12 @@ static inline u8 readb(const volatile void __iomem *addr)
 #define readw readw
 static inline u16 readw(const volatile void __iomem *addr)
 {
-	return __le16_to_cpu(__raw_readw(addr));
+	u16 val;
+
+	__io_br();
+	val = __le16_to_cpu(__raw_readw(addr));
+	__io_ar();
+	return val;
 }
 #endif
 
@@ -169,7 +179,12 @@ static inline u16 readw(const volatile void __iomem *addr)
 #define readl readl
 static inline u32 readl(const volatile void __iomem *addr)
 {
-	return __le32_to_cpu(__raw_readl(addr));
+	u32 val;
+
+	__io_br();
+	val = __le32_to_cpu(__raw_readl(addr));
+	__io_ar();
+	return val;
 }
 #endif
 
@@ -178,7 +193,12 @@ static inline u32 readl(const volatile void __iomem *addr)
 #define readq readq
 static inline u64 readq(const volatile void __iomem *addr)
 {
-	return __le64_to_cpu(__raw_readq(addr));
+	u64 val;
+
+	__io_br();
+	val = __le64_to_cpu(__raw_readq(addr));
+	__io_ar();
+	return val;
 }
 #endif
 #endif /* CONFIG_64BIT */
-- 
2.7.4