From: Mark Tomlinson <mark.tomlinson@alliedtelesis.co.nz>
To: paulburton@kernel.org, linux-mips@vger.kernel.org
Cc: chris.packham@alliedtelesis.co.nz, linux-kernel@vger.kernel.org,
Mark Tomlinson <mark.tomlinson@alliedtelesis.co.nz>
Subject: [PATCH] MIPS: cavium_octeon: Fix syncw generation.
Date: Wed, 12 Feb 2020 10:24:55 +1300 [thread overview]
Message-ID: <20200211212455.3307-1-mark.tomlinson@alliedtelesis.co.nz> (raw)
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>
---
arch/mips/include/asm/sync.h | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/arch/mips/include/asm/sync.h b/arch/mips/include/asm/sync.h
index 7c6a1095f5..aabd097933 100644
--- 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
--
2.25.0
next reply other threads:[~2020-02-11 21:25 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-11 21:24 Mark Tomlinson [this message]
2020-02-11 21:37 ` [PATCH] MIPS: cavium_octeon: Fix syncw generation Chris Packham
2020-02-15 22:55 ` Paul Burton
2020-02-17 0:22 ` Philippe Mathieu-Daudé
2020-02-17 4:58 ` Mark Tomlinson
2020-02-17 20:01 ` Chris Packham
2020-02-18 18:37 ` Nick Desaulniers
2020-02-20 15:28 ` Dmitry Golovin
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