p50_write_mbox_reg
ret = p50_write_mbox_reg(p50, P50_MBOX_REG_DATA, data);
ret = p50_write_mbox_reg(p50, P50_MBOX_REG_PARAM, param);
ret = p50_write_mbox_reg(p50, P50_MBOX_REG_CMD, cmd);
ret = p50_write_mbox_reg(p50, P50_MBOX_REG_CMD, P50_MBOX_CMD_CLEAR);