diff options
Diffstat (limited to 'Documentation/i2c/dev-interface')
| -rw-r--r-- | Documentation/i2c/dev-interface | 32 |
1 files changed, 14 insertions, 18 deletions
diff --git a/Documentation/i2c/dev-interface b/Documentation/i2c/dev-interface index d04e6e4964ee..fbed645ccd75 100644 --- a/Documentation/i2c/dev-interface +++ b/Documentation/i2c/dev-interface @@ -9,8 +9,8 @@ i2c adapters present on your system at a given time. i2cdetect is part of the i2c-tools package. I2C device files are character device files with major device number 89 -and a minor device number corresponding to the number assigned as -explained above. They should be called "i2c-%d" (i2c-0, i2c-1, ..., +and a minor device number corresponding to the number assigned as +explained above. They should be called "i2c-%d" (i2c-0, i2c-1, ..., i2c-10, ...). All 256 minor device numbers are reserved for i2c. @@ -23,11 +23,6 @@ First, you need to include these two headers: #include <linux/i2c-dev.h> #include <i2c/smbus.h> -(Please note that there are two files named "i2c-dev.h" out there. One is -distributed with the Linux kernel and the other one is included in the -source tree of i2c-tools. They used to be different in content but since 2012 -they're identical. You should use "linux/i2c-dev.h"). - Now, you have to decide which adapter you want to access. You should inspect /sys/class/i2c-dev/ or run "i2cdetect -l" to decide this. Adapter numbers are assigned somewhat dynamically, so you can not @@ -38,7 +33,7 @@ Next thing, open the device file, as follows: int file; int adapter_nr = 2; /* probably dynamically determined */ char filename[20]; - + snprintf(filename, 19, "/dev/i2c-%d", adapter_nr); file = open(filename, O_RDWR); if (file < 0) { @@ -72,8 +67,10 @@ the device supports them. Both are illustrated below. /* res contains the read word */ } - /* Using I2C Write, equivalent of - i2c_smbus_write_word_data(file, reg, 0x6543) */ + /* + * Using I2C Write, equivalent of + * i2c_smbus_write_word_data(file, reg, 0x6543) + */ buf[0] = reg; buf[1] = 0x43; buf[2] = 0x65; @@ -140,14 +137,14 @@ ioctl(file, I2C_RDWR, struct i2c_rdwr_ioctl_data *msgset) set in each message, overriding the values set with the above ioctl's. ioctl(file, I2C_SMBUS, struct i2c_smbus_ioctl_data *args) - Not meant to be called directly; instead, use the access functions - below. + If possible, use the provided i2c_smbus_* methods described below instead + of issuing direct ioctls. You can do plain i2c transactions by using read(2) and write(2) calls. You do not need to pass the address byte; instead, set it through ioctl I2C_SLAVE before you try to access the device. -You can do SMBus level transactions (see documentation file smbus-protocol +You can do SMBus level transactions (see documentation file smbus-protocol for details) through the following functions: __s32 i2c_smbus_write_quick(int file, __u8 value); __s32 i2c_smbus_read_byte(int file); @@ -158,7 +155,7 @@ for details) through the following functions: __s32 i2c_smbus_write_word_data(int file, __u8 command, __u16 value); __s32 i2c_smbus_process_call(int file, __u8 command, __u16 value); __s32 i2c_smbus_read_block_data(int file, __u8 command, __u8 *values); - __s32 i2c_smbus_write_block_data(int file, __u8 command, __u8 length, + __s32 i2c_smbus_write_block_data(int file, __u8 command, __u8 length, __u8 *values); All these transactions return -1 on failure; you can read errno to see what happened. The 'write' transactions return 0 on success; the @@ -166,10 +163,9 @@ what happened. The 'write' transactions return 0 on success; the returns the number of values read. The block buffers need not be longer than 32 bytes. -The above functions are all inline functions, that resolve to calls to -the i2c_smbus_access function, that on its turn calls a specific ioctl -with the data in a specific format. Read the source code if you -want to know what happens behind the screens. +The above functions are made available by linking against the libi2c library, +which is provided by the i2c-tools project. See: +https://git.kernel.org/pub/scm/utils/i2c-tools/i2c-tools.git/. Implementation details |