In case of DMA, If number of words to transfer are more than effective SPI FIFO Depth and is not a multiple of FIFO Depth, is not working.
Only remaining chunks of bytes which are not a multiple of FIFO Depth are not transferred.

For eg: FIFO Depth is 32bytes

Length is 100 Words, each word data size is 1byte.

Then number of words actually transferred is 96. Remaining 4 words is not transferred