how to make an edma request by gpmc module?

now ,i connect am335x with fpga by gpmc,i can   start  an EDMA  transmission  by cpu,but  i don't   konw  how to  send an EDMA request    by  fpga. i  set corresponding bit in EESRH,connect XDMA_EVENT_INTR1 to the FPGA,if FPGA give a high level to XDMA_EVENT_INTR1 ,i don't  konw  how to  send  an  edma request,give  high  level to XDMA_EVENT_INTR1 ,or a low level,or  a level jump .?do  i  have to change some code  in the linux kernel?who can help me?thank you very much !