Driver with hard RT requiremnets

Hello, We need to support serial driver with real time requirements (towards specific device with RT demands): Every 5.3msec receive 100 bytes and 1.3msec afterwards send 100 bytes. 1. Does kernel support real-time of such hard requirements ? 2. Is it matter if we do the exact bytes send/receive from kernel or userspace, i.e. is kernel more real-time than userspace ? 3. Is mainline kernel unable to support such requirements and we better use RT patch such as xemonai ? Best Regards, Ran