REG_DB_STAT
mb_chan->reg + REG_DB_STAT);
u32 val = readl(mb_chan->reg + REG_DB_STAT);
writel(MBOX_STATUS_ACK_MASK, mb_chan->reg + REG_DB_STAT);
u32 val = readl(mb_chan->reg + REG_DB_STAT);
writel(MBOX_STATUS_AVAIL_MASK, mb_chan->reg + REG_DB_STAT);