You may be having an issue due to needing to assign a bus to devices attached to the controller. Please see this example for a Dc390 with a cd and hdd attached.
-device dc390,id=scsi1
-device scsi-cd,bus=scsi1.0,drive=disk0
-drive if=none,id=disk0,media=cdrom,file=/y/A.iso
-device scsi-hd,bus=scsi1.0,drive=disk1
-drive if=none,id=disk1,media=disk,file=/n/.img,format=raw