Question regarding ISA DMA

Hi, I'm trying to understand how to use the ISA DMA with my PC. What I'm not able to understand is that why is it required to have an IRQ line associated with my device that is going to initiate the DMA? As I understand DMA controller would be signalling CPU[Correct?] so this IRQ would be handled by the ISA api? [Correct?]. What I don't understand is that how the device would know that DMA has been completed since device already has offloaded that work to DMA controller so why is it required to have an IRQ for the device? OR is it that I need to request_irq for DMA controller? Totally confused at this point. -- ---P.K.S