Stream-to-memory SGDMA does not write last QWord during a transfer

First you should check that you don't have any problems related to the CPU data cache when you read back the memory data. Ensure that you are using uncached access or that you invalidate the data cache on that memory area before you read.

Other than that I don't see anything irregular on your waves that would explain why the last word wouldn't be written. The only strange thing I see in your code in the use of a NULL pointer instead of a second descriptor to complete the chain. In most of the example codes they put a second descriptor chained to the first, even if it is just here to stop the SGDMA. I don't know how the DMA reacts to a NULL pointer as next descriptor.