ARM: 6741/1: errata: pl310 cache sync operation may be faulty

The effect of cache sync operation is to drain the store buffer and
wait for all internal buffers to be empty. In normal conditions, store
buffer is able to merge the normal memory writes within its 32-byte
data buffers.  Due to this erratum present in r3p0, the effect of cache
sync operation on the store buffer still remains when the operation
completes. This means that the store buffer is always asked to drain
and this prevents it from merging any further writes.

This can severely affect performance on the write traffic esp. on
Normal memory NC one.

The proposed workaround is to replace the normal offset of cache sync
operation(0x730) by another offset targeting an unmapped PL310
register 0x740.

Signed-off-by: srinidhi kasagar <srinidhi.kasagar@stericsson.com>
Acked-by: Linus Walleij <linus.walleij@stericsson.com>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

1 files changed, 6 insertions, 0 deletions

diff --git a/arch/arm/mm/cache-l2x0.c b/arch/arm/mm/cache-l2x0.c
index 170c9bb95866..f2ce38e085d2 100644
--- a/arch/arm/mm/cache-l2x0.c
+++ b/arch/arm/mm/cache-l2x0.c
@@ -49,7 +49,13 @@ static inline void cache_wait(void __iomem *reg, unsigned long mask)
 static inline void cache_sync(void)
 {
         void __iomem *base = l2x0_base;
+
+#ifdef CONFIG_ARM_ERRATA_753970
+        /* write to an unmmapped register */
+        writel_relaxed(0, base + L2X0_DUMMY_REG);
+#else
         writel_relaxed(0, base + L2X0_CACHE_SYNC);
+#endif
         cache_wait(base + L2X0_CACHE_SYNC, 1);
 }