Using the Linux kernel drivers is simply an economic decision. When using the latest lx_emul/lx_kit approach it tooks very few days to enable a new driver, and it tooks even less to update the code base, which is not the case with the deprecated dde_linux usb_host driver mentioned above. I hope you can understand this motivation. However, if you are strongly motivated to implement dedicated USB protocol stacks from scratch, I assume nobody will argue against it.
OK. I understand. It is just that I am unfamiliar with linux drivers. I will try a bit more. The rockchip kernel fais quite early in page table. I think I got around that, but reverted the change.