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ARM: dma-mapping: fix for speculative prefetching

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ARMv6 and ARMv7 CPUs can perform speculative prefetching, which makes
DMA cache coherency handling slightly more interesting.  Rather than
being able to rely upon the CPU not accessing the DMA buffer until DMA
has completed, we now must expect that the cache could be loaded with
possibly stale data from the DMA buffer.

Where DMA involves data being transferred to the device, we clean the
cache before handing it over for DMA, otherwise we invalidate the buffer
to get rid of potential writebacks.  On DMA Completion, if data was
transferred from the device, we invalidate the buffer to get rid of
any stale speculative prefetches.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Tested-By: Santosh Shilimkar <santosh.shilimkar@ti.com>
This commit is contained in:
Russell King
2009-10-31 16:52:16 +00:00
parent 702b94bff3
commit 2ffe2da3e7
3 changed files with 42 additions and 46 deletions
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10
arch/arm/mm/cache-v6.S
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@ -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
beq v6_dma_inv_range
b v6_dma_clean_range
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)