RCB_REG_HEAD
head = dsaf_read_dev(&qs->tx_ring, RCB_REG_HEAD);
head = readl_relaxed(ring->io_base + RCB_REG_HEAD);
int head = readl_relaxed(ring->io_base + RCB_REG_HEAD);
head = readl_relaxed(ring->io_base + RCB_REG_HEAD);
writel_relaxed(i, ring->io_base + RCB_REG_HEAD);
head = readl_relaxed(ring->io_base + RCB_REG_HEAD);