This went into 2.4 with the following comments..

ide-scsi driver starts DMA as soon as it writes the ATAPI PACKET command
in command register and before sending the ATAPI command. This will
cause problems on many drives. Right way to do it is to start DMA after
sending the ATAPI command. I am attaching a patch that fixes this. This
patch will allow many more CD-RW drives to work reliably in DMA mode
than do today

Alan's comment to this diff previously..
"Thats the least of the 2.5 ide-scsi problems, but yes its probably one to add"