res = i2c_transfer(client->adapter, rdwr_pa, rdwr_arg.nmsgs);这个函数具体是可以发送和读取数据的吗，还是说只是单单发送数据而已
I think u know the i2c_master_send & i2c_master_recv functions, both calling the i2c_transfer interface, so this func is used to send & write
msgs to device. As for u'll send or receive msg(s), depend on that the msg(struct i2c_msg) flag(I2C_M_RD, and others means write), please be known, enjoy your day