getting device descriptors / file handler in kernel space ?

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1

I've got some I2c stuff running from userspace. But originally I want
to write a kernel module, initialising all the i2c devices and handle
the transfer.
But what do I have to do to get a device descriptor / filehandler for /
dev/i2c-1 ... in a kernel module? open does not work ...
Same for writing/reading files ...

2

I’ve got some I2c stuff running from userspace.

Cool!

Would you mind sharing the necessary changes to enable access to the I2C port on the expansion connector?

(At least I assume this is what you are using)

Sharing the userspace code would also be very much appreciated!

John

3

Enabled i2c dev modules in the kernel?
Regards,
Nishanth Menon

4

No changes to do, just some lines in userspace. Take a look and the
i2c-tools
Some line added - far away from being perfect, just as an example.

But again to all others: How to do a fd=open("/dev/i2c_1",O_RDWR ) in
kernelspace or what is the way to get a file descriptor?

5

Sorry? The devices are available, otherwise I couldn't access them fro
userspace.
But I will do all this inside a driver, a loadable kernel module...

6

You need to use i2c_transfer API calls if you need to access it from
kernel space. see [1] for sample drivers. [2] is a very simplistic
usage.
Regards,
Nishanth Menon
[1] http://source.mvista.com/git/gitweb.cgi?p=linux-omap-2.6.git;a=tree;f=drivers/i2c/chips;h=57bb57541d7a35a3e21e582d788da878e0a3b9f8;hb=HEAD
[2] http://source.mvista.com/git/gitweb.cgi?p=linux-omap-2.6.git;a=blob;f=drivers/i2c/chips/gpio_expander_omap.c;h=dfe7f040fac261cf5983015a613541273b62f3a4;hb=HEAD

7

Please forgive my ignorance, but is there a mechanism to use i2c
userspace tools from kernel space?

I always thought one should write an i2c driver and client for the
related i2c device.

I remember in DaVinci tree there was a generic driver/client to
read/write from an i2c address. They were using this generic driver to
communicate with various devices like i2c expanders, msp430 based rtc,
etc. I used that driver to write a driver for tsc2004 touchscreen
controller.

Regards,
Caglar

8

There are two ways to access i2c:
a) using i2c-dev driver in kernel space and a userapp to interface to
the i2c-dev (this basically uses a "dummy client").
b) as you mentioned using the kernel client-driver architecture.
[1] has more information on the architecture in general.
Regards,
Nishanth Menon
[1] http://www.lm-sensors.org/wiki/Documentation

9

I did use the way you showed me - and it works. Thanks!
Originally I wanted to use the way at it was described in the kernel-
Docu:

res = i2c_smbus_read_word_data(file,register);

That's way I asked for the file descriptor...