diff options
Diffstat (limited to 'include/linux/i2c.h')
| -rw-r--r-- | include/linux/i2c.h | 51 |
1 files changed, 42 insertions, 9 deletions
diff --git a/include/linux/i2c.h b/include/linux/i2c.h index d4b63171d5d5..8fc4310f071b 100644 --- a/include/linux/i2c.h +++ b/include/linux/i2c.h @@ -443,19 +443,52 @@ static inline int i2c_adapter_id(struct i2c_adapter *adap) } #endif /* __KERNEL__ */ -/* - * I2C Message - used for pure i2c transaction, also from /dev interface +/** + * 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_TEN 0x10 /* we have a ten bit chip address */ -#define I2C_M_RD 0x01 -#define I2C_M_NOSTART 0x4000 -#define I2C_M_REV_DIR_ADDR 0x2000 -#define I2C_M_IGNORE_NAK 0x1000 -#define I2C_M_NO_RD_ACK 0x0800 -#define I2C_M_RECV_LEN 0x0400 /* length will be first received byte */ +#define I2C_M_TEN 0x0010 /* this is a ten bit chip address */ +#define I2C_M_RD 0x0001 /* read data, from slave to master */ +#define I2C_M_NOSTART 0x4000 /* if I2C_FUNC_PROTOCOL_MANGLING */ +#define I2C_M_REV_DIR_ADDR 0x2000 /* if I2C_FUNC_PROTOCOL_MANGLING */ +#define I2C_M_IGNORE_NAK 0x1000 /* if I2C_FUNC_PROTOCOL_MANGLING */ +#define I2C_M_NO_RD_ACK 0x0800 /* if I2C_FUNC_PROTOCOL_MANGLING */ +#define I2C_M_RECV_LEN 0x0400 /* length will be first received byte */ __u16 len; /* msg length */ __u8 *buf; /* pointer to msg data */ }; |
