From: Mark Tomlinson mark.tomlinson@alliedtelesis.co.nz
commit 97e914b7de3c943011779b979b8093fdc0d85722 upstream.
The Cavium Octeon CPU uses a special sync instruction for implementing wmb, and due to a CPU bug, the instruction must appear twice. A macro had been defined to hide this:
#define __SYNC_rpt(type) (1 + (type == __SYNC_wmb))
which was intended to evaluate to 2 for __SYNC_wmb, and 1 for any other type of sync. However, this expression is evaluated by the assembler, and not the compiler, and the result of '==' in the assembler is 0 or -1, not 0 or 1 as it is in C. The net result was wmb() producing no code at all. The simple fix in this patch is to change the '+' to '-'.
Fixes: bf92927251b3 ("MIPS: barrier: Add __SYNC() infrastructure") Signed-off-by: Mark Tomlinson mark.tomlinson@alliedtelesis.co.nz Tested-by: Chris Packham chris.packham@alliedtelesis.co.nz Signed-off-by: Paul Burton paulburton@kernel.org Cc: linux-mips@vger.kernel.org Cc: linux-kernel@vger.kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- arch/mips/include/asm/sync.h | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)
--- a/arch/mips/include/asm/sync.h +++ b/arch/mips/include/asm/sync.h @@ -155,9 +155,11 @@ * effective barrier as noted by commit 6b07d38aaa52 ("MIPS: Octeon: Use * optimized memory barrier primitives."). Here we specify that the affected * sync instructions should be emitted twice. + * Note that this expression is evaluated by the assembler (not the compiler), + * and that the assembler evaluates '==' as 0 or -1, not 0 or 1. */ #ifdef CONFIG_CPU_CAVIUM_OCTEON -# define __SYNC_rpt(type) (1 + (type == __SYNC_wmb)) +# define __SYNC_rpt(type) (1 - (type == __SYNC_wmb)) #else # define __SYNC_rpt(type) 1 #endif