mxs_mmc_prep_dma
desc = mxs_mmc_prep_dma(host, MXS_DMA_CTRL_WAIT4END);
desc = mxs_mmc_prep_dma(host, MXS_DMA_CTRL_WAIT4END);
desc = mxs_mmc_prep_dma(host, 0);
desc = mxs_mmc_prep_dma(host, DMA_PREP_INTERRUPT | MXS_DMA_CTRL_WAIT4END);