Either the data isn't getting written to the buffer correctly or else the buffer isn't getting sent to the device correctly. Can anybody suggest a means of determining which is the case?
I can't say anything about this log that including only DMA addresses. I'm not familiar with how the USB core does DMA stuff. And the USB stack design that the USB core does DMA stuff (allocating, mappings, etc) makes debugging DMA issues really difficult.
The DMA stuff is simple enough in this case. The urb->transfer_buffer address is passed to dma_map_single(), and the DMA address it returns is stored in urb->transfer_dma. Those are the two values printed out by the debugging patch.
Is that address (urb->transfer_dma) the same as 'virt_to_phys(urb->transfer_buffer)' (if not, then SWIOTLB is being utilized) and is the dma_sync_* done on the urb->transfer_dma (to properly sync the data from the SWIOTLB to the transfer_buffer) before you start using the urb->transfer_buffer?