i2c: update i2c-dev.h warning in documentation

dev-interface document gives examples for accessing i2c from userspace.

There's a note warning developers about the different i2c-dev.h header files which were shipped with the kernel and i2c-tools separately.

However, these commits in i2c-tools repository suggests that the header files are now identical (in functionality) and i2c_* functions are now defined in a separate header called i2c/smbus.h, which is distributed with i2c-tools:

commit 652619121974 ("Minimize differences with kernel flavor") commit 93caf007f4cb ("Move SMBus helper functions to include/i2c/smbus.h")

Thus, I've converted the warning paragraph into a historical note and updated the suggested header files.

---
 Documentation/i2c/dev-interface | 29 ++++++++++++++++-------------
 1 file changed, 16 insertions(+), 13 deletions(-)

b/Documentation/i2c/dev-interface index 5ff19447ac44..04d110697863 100644 --- a/Documentation/i2c/dev-interface
+++ b/Documentation/i2c/dev-interface
@@ -9,21 +9,24 @@ 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.

C example
=========

-So let's say you want to access an i2c adapter from a C program. The -first thing to do is "#include <linux/i2c-dev.h>". Please note that -there are two files named "i2c-dev.h" out there, one is distributed -with the Linux kernel and is meant to be included from kernel -driver code, the other one is distributed with i2c-tools and is -meant to be included from user-space programs. You obviously want -the second one here.
+So let's say you want to access an i2c adapter from a C program. 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.
@@ -35,7 +38,7 @@ 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) {
@@ -69,7 +72,7 @@ the device supports them. Both are illustrated below.

     /* res contains the read word */

}

- /* Using I2C Write, equivalent of
+ /* Using I2C Write, equivalent of

      i2c_smbus_write_word_data(file, reg, 0x6543) */

buf[0] = reg;
buf[1] = 0x43;
@@ -144,7 +147,7 @@ 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);
@@ -155,7 +158,7 @@ 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

2.15.1