linux-kernel - [PATCH v4 2/2] MIPS: io: add a barrier after register read in readX()

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Date:   Thu, 12 Apr 2018 22:30:44 -0400
From:   Sinan Kaya <okaya@...eaurora.org>
To:     linux-mips@...ux-mips.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>,
        Ralf Baechle <ralf@...ux-mips.org>,
        James Hogan <jhogan@...nel.org>,
        Paul Burton <paul.burton@...s.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH v4 2/2] MIPS: io: add a barrier after register read in readX()

While a barrier is present in writeX() function before the register write,
a similar barrier is missing in the readX() function after the register
read. This could allow memory accesses following readX() to observe
stale data.

Signed-off-by: Sinan Kaya <okaya@...eaurora.org>
Reported-by: Arnd Bergmann <arnd@...db.de>
---
 arch/mips/include/asm/io.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/mips/include/asm/io.h b/arch/mips/include/asm/io.h
index fd00ddaf..d96af41 100644
--- a/arch/mips/include/asm/io.h
+++ b/arch/mips/include/asm/io.h
@@ -377,6 +377,8 @@ static inline type pfx##read##bwlq(const volatile void __iomem *mem)	\
 		BUG();							\
 	}								\
 									\
+	/* prevent prefetching of coherent DMA dma prematurely */	\
+	rmb();								\
 	return pfx##ioswab##bwlq(__mem, __val);				\
 }
 
-- 
2.7.4