MIPS: io: Add barrier after register read in readX()

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

Signed-off-by: Sinan Kaya <okaya@codeaurora.org>
Reported-by: Arnd Bergmann <arnd@arndb.de>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Paul Burton <paul.burton@mips.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/19069/
[jhogan@kernel.org: Tidy commit message]
Signed-off-by: James Hogan <jhogan@kernel.org>

diff --git a/arch/mips/include/asm/io.h b/arch/mips/include/asm/io.h
index fd00dda..a7d0b83 100644 (file)
--- 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 data prematurely */      \
+       rmb();                                                          \
        return pfx##ioswab##bwlq(__mem, __val);                         \
 }