dmaengine_prep_slave_sg

The interface has the following parameters.

Synopsis:

static inline struct dma_async_tx_descriptor *
        dmaengine_prep_slave_sg(struct dma_chan *chan, 
                                struct scatterlist *sgl,
                                unsigned int sg_len,
                                enum dma_transfer_direction dir,
                                unsigned long flags)

Description: The interface is used to prepare a DMA transmission for the scattered buffer.
Parameter:
- chan: The relevant DMA channel.
- sgl: The address of the scattered transmission list. The list should be created before a scattered transmission.
- dir: Transmission direction. For example:
  - DMA_MEM_TO_DEV: From memory to device.
  - DMA_DEV_TO_MEM: From device to memory.
- flags: The macro definitions started with "DMA_PREP_", which provides additional information for the DMA Controller (DMAC) driver. For example:
  - DMA_PREP_INTERRUPT: The flag is used to inform DMAC that an interrupt will be generated after the transmission, so that DMAC will use the callback function from the client.
  - DMA_PREP_FENCE: The flag is used to inform DMAC that all the later transmissions rely on the success of the current transmission, so that DMAC will prioritize the DMA transmissions accordingly.
Return:
- Success: A pointer to the transmission descriptor.
- Failure: NULL.