cfg_pointer
#define cfg_write8(reg, item, val) iowrite8(val, cfg_pointer(reg, item))
#define cfg_write16(reg, item, val) iowrite16(val, cfg_pointer(reg, item))
#define cfg_write32(reg, item, val) iowrite32(val, cfg_pointer(reg, item))
#define cfg_write64(reg, item, val) iowrite64_lo_hi(val, cfg_pointer(reg, item))
#define cfg_read8(reg, item) ioread8(cfg_pointer(reg, item))
#define cfg_read32(reg, item) ioread32(cfg_pointer(reg, item))
#define cfg_read64(reg, item) ioread64(cfg_pointer(reg, item))