Linux Kernel 设备驱动之I2C之client之发送消息格式

前面host两种传输方式对应了两种消息格式：i2c_msg和i2c_smbus_data /**  * struct i2c_msg - an I2C transaction segment beginning with START  * @addr: Slave address, either seven or ten bits.  When this is a ten  * bit address, I2C_M_TEN must be set in @flags and the adapter  * must support I2C_FUNC_10BIT_ADDR.  * @flags: I2C_M_RD is handled by all adapters.  No other flags may be  * provided unless the adapter exported the relevant I2C_FUNC_*  * flags through i2c_check_functionality().  * @len: Number of data bytes in @buf being read from or written to the  * I2C slave address.  For read transactions where I2C_M_RECV_LEN  * is set, the caller guarantees that this buffer can hold up to  * 32 bytes in addition to the initial length byte sent by the  * slave (plus, if used, the SMBus PEC); and this value will be  * incremented by the number of block data bytes received.  * @buf: The buffer into which data is read, or from which it's written.  *  * An i2c_msg is the low level representation of one segment of an I2C  * transaction.  It is visible to drivers in the @i2c_transfer() procedure,  * to userspace from i2c-dev, and to I2C adapter drivers through the  * @i2c_adapter.@master_xfer() method.  *  * Except when I2C "protocol mangling" is used, all I2C adapters implement  * the standard rules for I2C transactions.  Each transaction begins with a  * START.  That is followed by the slave address, and a bit encoding read  * versus write.  Then follow all the data bytes, possibly including a byte  * with SMBus PEC.  The transfer terminates with a NAK, or when all those  * bytes have been transferred and ACKed.  If this is the last message in a  * group, it is followed by a STOP.  Otherwise it is followed by the next  * @i2c_msg transaction segment, beginning with a (repeated) START.  *  * Alternatively, when the adapter supports I2C_FUNC_PROTOCOL_MANGLING then  * passing certain @flags may have changed those standard protocol behaviors.  * Those flags are only for use with broken/nonconforming slaves, and with  * adapters which are known to support the specific mangling options they  * need (one or more of IGNORE_NAK, NO_RD_ACK, NOSTART, and REV_DIR_ADDR).  */ struct i2c_msg {  __u16 addr; /* slave address   */  __u16 flags; #define I2C_M_RD  0x0001 /* read data, from slave to master */      /* I2C_M_RD is guaranteed to be 0x0001! */ #define I2C_M_TEN  0x0010 /* this is a ten bit chip address */ #define I2C_M_RECV_LEN  0x0400 /* length will be first received byte */ #define I2C_M_NO_RD_ACK  0x0800 /* if I2C_FUNC_PROTOCOL_MANGLING */ #define I2C_M_IGNORE_NAK 0x1000 /* if I2C_FUNC_PROTOCOL_MANGLING */ #define I2C_M_REV_DIR_ADDR 0x2000 /* if I2C_FUNC_PROTOCOL_MANGLING */ #define I2C_M_NOSTART  0x4000 /* if I2C_FUNC_NOSTART */ #define I2C_M_STOP  0x8000 /* if I2C_FUNC_PROTOCOL_MANGLING */  __u16 len;  /* msg length    */  __u8 *buf;  /* pointer to msg data   */ };   /*  * Data for SMBus Messages  */ #define I2C_SMBUS_BLOCK_MAX 32 /* As specified in SMBus standard */ union i2c_smbus_data {  __u8 byte;  __u16 word;  __u8 block[I2C_SMBUS_BLOCK_MAX + 2]; /* block[0] is used for length */           /* and one more for user-space compatibility */ };