dma_transfer
INIT_WORK(&vindev->dma_work, dma_transfer);
INIT_WORK(&voutdev->dma_work, dma_transfer);
return dws->dma_ops->dma_transfer(dws, transfer);
.dma_transfer = dw_spi_dma_transfer,
.dma_transfer = dw_spi_dma_transfer,
int (*dma_transfer)(struct dw_spi *dws, struct spi_transfer *xfer);