RING_REGS_SIZE
if (!iomem || (resource_size(iomem) < RING_REGS_SIZE)) {
for (regs = mbox->regs; regs < regs_end; regs += RING_REGS_SIZE) {
regs += RING_REGS_SIZE;
regs += RING_REGS_SIZE;
ring < (reg->ioaddr + reg->size); ring += RING_REGS_SIZE) {