Currently, Documentation/i2c/dev-interface describes the use of i2c_smbus_*
helper routines as static inlined functions provided by linux/i2c-dev.h. Work
has been done to refactor the linux/i2c-dev.h file in the i2c-tools project
out into its own library. As a result, these docs have become stale.
This patch corrects the discrepancy and directs the reader to the i2c-tools
project for more information. Additionally, some trailing-whitespace cleanups
were made.
Signed-off-by: Sam Hansen <hansens@xxxxxxxxxx>
---
Documentation/i2c/dev-interface | 28 +++++++++++-----------------
1 file changed, 11 insertions(+), 17 deletions(-)
diff --git a/Documentation/i2c/dev-interface b/Documentation/i2c/dev-interface
index d04e6e4964ee..5323588fe99d 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) {
@@ -72,7 +67,7 @@ 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;
@@ -140,14 +135,14 @@ 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 in favor
+ 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 +153,7 @@ 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 +161,9 @@ 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
--
2.17.0.484.g0c8726318c-goog
--
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