关于DMA驱动的问题

mzxiao123

我在写一个DMA驱动，请教一下下面的DMA操作类型到底各是什么意思呢？
特别是DMA_SLAVE，DMA_CYCLIC，DMA_INTERRUPT，DMA_PRIVATE。
也不明白device_prep_dma_sg()跟device_prep_slave_sg()的区别。

/**
* enum dma_transaction_type - DMA transaction types/indexes
*
* Note: The DMA_ASYNC_TX capability is not to be set by drivers.  It is
* automatically set as dma devices are registered.
*/
enum dma_transaction_type {
        DMA_MEMCPY,
        DMA_XOR,
        DMA_PQ,
        DMA_XOR_VAL,
        DMA_PQ_VAL,
        DMA_INTERRUPT,
        DMA_SG,
        DMA_PRIVATE,
        DMA_ASYNC_TX,
        DMA_SLAVE,
        DMA_CYCLIC,
        DMA_INTERLEAVE,
/* last transaction type for creation of the capabilities mask */
        DMA_TX_TYPE_END,
};

        struct dma_async_tx_descriptor *(*device_prep_dma_sg)(
                struct dma_chan *chan,
                struct scatterlist *dst_sg, unsigned int dst_nents,
                struct scatterlist *src_sg, unsigned int src_nents,
                unsigned long flags);

        struct dma_async_tx_descriptor *(*device_prep_slave_sg)(
                struct dma_chan *chan, struct scatterlist *sgl,
                unsigned int sg_len, enum dma_transfer_direction direction,
                unsigned long flags, void *context);