Follow linux dma flow:
Before DMA read, be sure to invalidate the cache over the address
range of DMA buffer to prevent cache coherency problems.
After DMA read, invalidate dcache again.
Signed-off-by: Peng Fan <Peng.Fan@freescale.com>
Acked-by: Marek Vasut <marex@denx.de>
Acked-by: Tim Harvey <tharvey@gateworks.com>
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