[PATCH] armv6: invalidate cache on DMA_FROM_DEVICE/DMA_BIDIRECTIONAL

[Jamie Iles]

Some ARMv6 cores will use speculative prefetching. This can be a problem
when devices DMA to memory and the core prefetches data before the
device has written it. This can result in stale data being stored in the
cache. The DMA API will request the invalidation but this is currently a
no-op on v6. Use the same dma_unmap_area implementation as for v7.

Additionally, simplify v6_dma_map_area() so that we clean the cache lines
for DMA_TO_DEVICE and DMA_FROM_DEVICE but don't do any invalidation. This
will be done when we unmap.

Signed-off-by: Jamie Iles <jamie.iles at picochip.com>
Cc: Russell King <rmk+kernel at arm.linux.org.uk>
---
 arch/arm/mm/cache-v6.S |   10 ++++++----
 1 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/arch/arm/mm/cache-v6.S b/arch/arm/mm/cache-v6.S
index a11934e..1dd9e0e 100644
--- a/arch/arm/mm/cache-v6.S
+++ b/arch/arm/mm/cache-v6.S
@@ -271,10 +271,9 @@ ENTRY(v6_dma_flush_range)
  */
 ENTRY(v6_dma_map_area)
 	add	r1, r1, r0
-	cmp	r2, #DMA_TO_DEVICE
-	beq	v6_dma_clean_range
-	bcs	v6_dma_inv_range
-	b	v6_dma_flush_range
+	teq	r2, #DMA_FROM_DEVICE
+	bne	v6_dma_clean_range
+	mov	pc, lr
 ENDPROC(v6_dma_map_area)
 
 /*
@@ -284,6 +283,9 @@ ENDPROC(v6_dma_map_area)
  *	- dir	- DMA direction
  */
 ENTRY(v6_dma_unmap_area)
+	add	r1, r1, r0
+	teq	r2, #DMA_TO_DEVICE
+	bne	v6_dma_inv_range
 	mov	pc, lr
 ENDPROC(v6_dma_unmap_area)
 
-- 
1.6.5.4