> > +		dma_descriptor_unmap(&desc->async_tx);
>
> Does callback function still use these data? suppose should unmap after
> callback return.

Actually, the opposite is true. Drivers have been fixed to use this
order. One example:

commit 9b335978f7081cd4fe264709599a18073e12fee2
Author: Dave Jiang <dave.jiang@intel.com>
Date:   Mon Jul 25 10:33:57 2016 -0700

    dmaengine: fsldma: move unmap to before callback

    Completion callback should happen after dma_descriptor_unmap() has
    happened. This allow the cache invalidate to happen and ensure that
    the data accessed by the upper layer is in memory that was from DMA
    rather than stale data. On some architecture this is done by the
    hardware, however we should make the code consistent to not cause
    confusion.

    Signed-off-by: Dave Jiang <dave.jiang@intel.com>
    Acked-by: Li Yang <leoyang.li@nxp.com>
    Signed-off-by: Vinod Koul <vinod.koul@intel.com>