Unified Driver model for low speed and high speed microcontrollers with limited and good memory [on hold]

I am trying to develop an experimental RTOS. I am stuck in the driver layer design. I want to make the driver layer libraries friendly for the other layers but then again I would like to have high performance. I have narrowed this down to a mixture of 2 approaches. The first is to have a structure for the controller with callbacks as elements. For eg:

struct peripheral_controller { 
    int32_t (*init) (struct peripheral_instance_regs *peripheral_instance_regs);
    int32_t (*isFull) (struct peripheral_instance_regs *peripheral_instance_regs);
};

The second approach is to have helper macros which take the peripheral_instance_regs as arguements.

For eg:

#define isFull(reg)
 (reg&0x01 == 1)

Is this the right approach? Will it confuse the users of my library? The problem with the callbacks as I see is in the interrupt routine where I would not want to call any functions.