utils.h:
#ifndef DRV_UTILS_H_
#define DRV_UTILS_H_
#include <stdint.h>

typedef void (*voidptr)(void);
typedef uint16_t(*uint16ptr)(uint8_t);

#endif /* MIFARE_DRV_UTILS_H_ */


spi.h:
#ifndef MIFARE_DRV_SPI_H_
#define MIFARE_DRV_SPI_H_
#include "utils.h"
//typedef void (*voidptr)(void);

typedef struct spiapi {
    voidptr   assert;   // <- unknown type name 'voidptr'
    voidptr   deassert;
    voidptr   reset;
    voidptr   init;
    uint16ptr txrx;     // <- this is ok
} SPI_API_T;

extern void hspi_init (void);
extern uint16_t hspi_transmit(uint8_t data);

#endif /* MIFARE_DRV_SPI_H_ */