PCIe devices can read or write to memory, i.e. can do DMA without requiring a device driver. If I remember correctly, if you flash a device's firmware (let's say an FPGA device) and input 0xFFFF as device and vendor ID, the device won't be enumerated by BIOS. I am wondering, if a PCIe device can conduct DMA operations (memory read and write) by bus mastering even when it is not enumerated by BIOS.
