linux-kernel - [PATCH v2 2/2] parisc: define stronger ordering for the default readX()

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Date:   Tue, 17 Apr 2018 00:08:51 -0400
From:   Sinan Kaya <okaya@...eaurora.org>
To:     linux-parisc@...r.kernel.org, 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>,
        "James E.J. Bottomley" <jejb@...isc-linux.org>,
        Helge Deller <deller@....de>,
        Philippe Ombredanne <pombredanne@...b.com>,
        Kate Stewart <kstewart@...uxfoundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org
Subject: [PATCH v2 2/2] parisc: define stronger ordering for the default readX()

parisc architecture seems to be mapping readX() and readX_relaxed() APIs
to __raw_readX() API.

__raw_readX() API doesn't provide any kind of ordering guarantees.
commit 032d59e1cde9 ("io: define stronger ordering for the default readX()
implementation") changed asm-generic implementation to use a more
conservative approach towards the readX() API.

Place a barrier() after the register read so that compiler doesn't
optimize across the regiter operation.

Signed-off-by: Sinan Kaya <okaya@...eaurora.org>
---
 arch/parisc/include/asm/io.h | 23 +++++++++++++++++++----
 1 file changed, 19 insertions(+), 4 deletions(-)

diff --git a/arch/parisc/include/asm/io.h b/arch/parisc/include/asm/io.h
index 2ec6405..e04c4ef 100644
--- a/arch/parisc/include/asm/io.h
+++ b/arch/parisc/include/asm/io.h
@@ -179,19 +179,34 @@ static inline void __raw_writeq(unsigned long long b, volatile void __iomem *add
 
 static inline unsigned char readb(const volatile void __iomem *addr)
 {
-	return __raw_readb(addr);
+	unsigned char ret;
+
+	ret = __raw_readb(addr);
+	barrier();
+	return ret;
 }
 static inline unsigned short readw(const volatile void __iomem *addr)
 {
-	return le16_to_cpu((__le16 __force) __raw_readw(addr));
+	unsigned short ret;
+
+	ret = le16_to_cpu((__le16 __force) __raw_readw(addr));
+	barrier();
+	return ret;
 }
 static inline unsigned int readl(const volatile void __iomem *addr)
 {
-	return le32_to_cpu((__le32 __force) __raw_readl(addr));
+	unsigned int ret;
+	ret = le32_to_cpu((__le32 __force) __raw_readl(addr));
+	barrier();
+	return ret;
 }
 static inline unsigned long long readq(const volatile void __iomem *addr)
 {
-	return le64_to_cpu((__le64 __force) __raw_readq(addr));
+	unsigned long long ret;
+
+	ret = le64_to_cpu((__le64 __force) __raw_readq(addr));
+	barrier();
+	return ret;
 }
 
 static inline void writeb(unsigned char b, volatile void __iomem *addr)
-- 
2.7.4