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, 15 insertions, 0 deletions

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 26d45e5b636b..ba9fc213f344 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -1177,6 +1177,21 @@ config ARM_ERRATA_743622
           visible impact on the overall performance or power consumption of the
           processor.
 
+config ARM_ERRATA_753970
+        bool "ARM errata: cache sync operation may be faulty"
+        depends on CACHE_PL310
+        help
+          This option enables the workaround for the 753970 PL310 (r3p0) erratum.
+
+          Under some condition 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. The workaround
+          is to replace the normal offset of cache sync operation (0x730)
+          by another offset targeting an unmapped PL310 register 0x740.
+          This has the same effect as the cache sync operation: store buffer
+          drain and waiting for all buffers empty.
+
 endmenu
 
 source "arch/arm/common/Kconfig"