Getting a DMA channel on x86 for a PCIe transfer

Hi, I want to transfer data from the RAM to a BAR with memory space of a PCIe Endpoint over a DMA on a x86 System. But currently I am failing to get a channel of a DMA controller. In the probe function, I tried to requst a DMA channel with: dma_cap_zero(mask); dma_cap_set(DMA_SLAVE | DMA_PRIVATE, mask); chan = dma_request_channel(mask, NULL, NULL); and also with: chan = dma_request_chan(&pdev->dev, pci_name(pdev)); But in both cases IS_ERR_OR_NULL(chn) is true, so I am not getting a valid DMA channel. What am I doing wrong? How to get a DMA channel on a x86 system? Best regards, Johannes