SPI_MRBLR
fsl_dummy_rx = kmalloc(SPI_MRBLR, GFP_KERNEL);
mspi->dma_dummy_rx = dma_map_single(dev, fsl_dummy_rx, SPI_MRBLR,
iowrite16be(SPI_MRBLR, &mspi->pram->mrblr);
dma_unmap_single(dev, mspi->dma_dummy_rx, SPI_MRBLR, DMA_FROM_DEVICE);
unsigned int xfer_len = min(mspi->count, SPI_MRBLR);