[PATCH 5.5 114/176] MIPS: cavium_octeon: Fix syncw generation.

Greg Kroah-Hartman
2020-03-03T18:12:01Z

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