Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1 | INTRODUCTION |
| 2 | ------------ |
| 3 | |
| 4 | Because not every I2C or SMBus adapter implements everything in the |
| 5 | I2C specifications, a client can not trust that everything it needs |
| 6 | is implemented when it is given the option to attach to an adapter: |
| 7 | the client needs some way to check whether an adapter has the needed |
| 8 | functionality. |
| 9 | |
| 10 | |
| 11 | FUNCTIONALITY CONSTANTS |
| 12 | ----------------------- |
| 13 | |
| 14 | For the most up-to-date list of functionality constants, please check |
| 15 | <linux/i2c.h>! |
| 16 | |
| 17 | I2C_FUNC_I2C Plain i2c-level commands (Pure SMBus |
| 18 | adapters typically can not do these) |
| 19 | I2C_FUNC_10BIT_ADDR Handles the 10-bit address extensions |
Hideki Iwamoto | d057c96 | 2005-09-25 16:53:04 +0200 | [diff] [blame^] | 20 | I2C_FUNC_PROTOCOL_MANGLING Knows about the I2C_M_IGNORE_NAK, |
| 21 | I2C_M_REV_DIR_ADDR, I2C_M_NOSTART and |
| 22 | I2C_M_NO_RD_ACK flags (which modify the |
| 23 | I2C protocol!) |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 24 | I2C_FUNC_SMBUS_QUICK Handles the SMBus write_quick command |
| 25 | I2C_FUNC_SMBUS_READ_BYTE Handles the SMBus read_byte command |
| 26 | I2C_FUNC_SMBUS_WRITE_BYTE Handles the SMBus write_byte command |
| 27 | I2C_FUNC_SMBUS_READ_BYTE_DATA Handles the SMBus read_byte_data command |
| 28 | I2C_FUNC_SMBUS_WRITE_BYTE_DATA Handles the SMBus write_byte_data command |
| 29 | I2C_FUNC_SMBUS_READ_WORD_DATA Handles the SMBus read_word_data command |
| 30 | I2C_FUNC_SMBUS_WRITE_WORD_DATA Handles the SMBus write_byte_data command |
| 31 | I2C_FUNC_SMBUS_PROC_CALL Handles the SMBus process_call command |
| 32 | I2C_FUNC_SMBUS_READ_BLOCK_DATA Handles the SMBus read_block_data command |
| 33 | I2C_FUNC_SMBUS_WRITE_BLOCK_DATA Handles the SMBus write_block_data command |
| 34 | I2C_FUNC_SMBUS_READ_I2C_BLOCK Handles the SMBus read_i2c_block_data command |
| 35 | I2C_FUNC_SMBUS_WRITE_I2C_BLOCK Handles the SMBus write_i2c_block_data command |
| 36 | |
| 37 | A few combinations of the above flags are also defined for your convenience: |
| 38 | |
| 39 | I2C_FUNC_SMBUS_BYTE Handles the SMBus read_byte |
| 40 | and write_byte commands |
| 41 | I2C_FUNC_SMBUS_BYTE_DATA Handles the SMBus read_byte_data |
| 42 | and write_byte_data commands |
| 43 | I2C_FUNC_SMBUS_WORD_DATA Handles the SMBus read_word_data |
| 44 | and write_word_data commands |
| 45 | I2C_FUNC_SMBUS_BLOCK_DATA Handles the SMBus read_block_data |
| 46 | and write_block_data commands |
| 47 | I2C_FUNC_SMBUS_I2C_BLOCK Handles the SMBus read_i2c_block_data |
| 48 | and write_i2c_block_data commands |
| 49 | I2C_FUNC_SMBUS_EMUL Handles all SMBus commands than can be |
| 50 | emulated by a real I2C adapter (using |
| 51 | the transparent emulation layer) |
| 52 | |
| 53 | |
| 54 | ALGORITHM/ADAPTER IMPLEMENTATION |
| 55 | -------------------------------- |
| 56 | |
| 57 | When you write a new algorithm driver, you will have to implement a |
| 58 | function callback `functionality', that gets an i2c_adapter structure |
| 59 | pointer as its only parameter: |
| 60 | |
| 61 | struct i2c_algorithm { |
| 62 | /* Many other things of course; check <linux/i2c.h>! */ |
| 63 | u32 (*functionality) (struct i2c_adapter *); |
| 64 | } |
| 65 | |
| 66 | A typically implementation is given below, from i2c-algo-bit.c: |
| 67 | |
| 68 | static u32 bit_func(struct i2c_adapter *adap) |
| 69 | { |
| 70 | return I2C_FUNC_SMBUS_EMUL | I2C_FUNC_10BIT_ADDR | |
| 71 | I2C_FUNC_PROTOCOL_MANGLING; |
| 72 | } |
| 73 | |
| 74 | |
| 75 | |
| 76 | CLIENT CHECKING |
| 77 | --------------- |
| 78 | |
| 79 | Before a client tries to attach to an adapter, or even do tests to check |
| 80 | whether one of the devices it supports is present on an adapter, it should |
| 81 | check whether the needed functionality is present. There are two functions |
| 82 | defined which should be used instead of calling the functionality hook |
| 83 | in the algorithm structure directly: |
| 84 | |
| 85 | /* Return the functionality mask */ |
| 86 | extern u32 i2c_get_functionality (struct i2c_adapter *adap); |
| 87 | |
| 88 | /* Return 1 if adapter supports everything we need, 0 if not. */ |
| 89 | extern int i2c_check_functionality (struct i2c_adapter *adap, u32 func); |
| 90 | |
| 91 | This is a typical way to use these functions (from the writing-clients |
| 92 | document): |
| 93 | int foo_detect_client(struct i2c_adapter *adapter, int address, |
| 94 | unsigned short flags, int kind) |
| 95 | { |
| 96 | /* Define needed variables */ |
| 97 | |
| 98 | /* As the very first action, we check whether the adapter has the |
| 99 | needed functionality: we need the SMBus read_word_data, |
| 100 | write_word_data and write_byte functions in this example. */ |
| 101 | if (!i2c_check_functionality(adapter,I2C_FUNC_SMBUS_WORD_DATA | |
| 102 | I2C_FUNC_SMBUS_WRITE_BYTE)) |
| 103 | goto ERROR0; |
| 104 | |
| 105 | /* Now we can do the real detection */ |
| 106 | |
| 107 | ERROR0: |
| 108 | /* Return an error */ |
| 109 | } |
| 110 | |
| 111 | |
| 112 | |
| 113 | CHECKING THROUGH /DEV |
| 114 | --------------------- |
| 115 | |
| 116 | If you try to access an adapter from a userspace program, you will have |
| 117 | to use the /dev interface. You will still have to check whether the |
| 118 | functionality you need is supported, of course. This is done using |
Jean Delvare | 014e453 | 2005-07-28 23:08:43 +0200 | [diff] [blame] | 119 | the I2C_FUNCS ioctl. An example, adapted from the lm_sensors i2cdetect |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 120 | program, is below: |
| 121 | |
| 122 | int file; |
| 123 | if (file = open("/dev/i2c-0",O_RDWR) < 0) { |
| 124 | /* Some kind of error handling */ |
| 125 | exit(1); |
| 126 | } |
| 127 | if (ioctl(file,I2C_FUNCS,&funcs) < 0) { |
| 128 | /* Some kind of error handling */ |
| 129 | exit(1); |
| 130 | } |
| 131 | if (! (funcs & I2C_FUNC_SMBUS_QUICK)) { |
| 132 | /* Oops, the needed functionality (SMBus write_quick function) is |
| 133 | not available! */ |
| 134 | exit(1); |
| 135 | } |
| 136 | /* Now it is safe to use the SMBus write_quick command */ |