Question on allocating to USB devices

[Noam Liron <lnoam@xxxxxxxxxxx>]

I am working on a SOC which it's RAM starts at 0x200M. For some reason I need to limit the DMA allocations up to 0x220M, and I've done it by creating a shared DMA pool in the DTS:
reserved-memory {
    #address-cells = <2>;
    #size-cells = <2>;
    ranges;

    reserved: buffer@0 {
        compatible = "shared-dma-pool"; 
        no-map;
    reg = <0x2 0x0 0x0 0x1000000>;
}
which each platform driver in the DTS uses, by referencing the pool:

memory-region = <&reserved>;

But how can I enforce allocation from this pool (or other reserved area) of usb devices such as usb2eth dongle? After all they are also devices (probed at usbnet_probe) that allocate DMA, but are not represented at the DTS.