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I'd like to write an I2C driver for a sensor device. There is a non-zero conversion time, and I don't want to waste kernel time to wait and poll busy state until the device is busy.

I thought I setup a timer and call the update time to time.

However the whole system freezes when execution reaches any I2C function.

I prepared a really simplified example, which is not working. Everything fine until the I2C access.

http://pastebin.com/kP5LCK2c

Without I2C stuff, the code works. Without the timer stuff, I2C works.

I did not find how to use I2C in an asynchronous (non-blocking) manner.

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As the i2c functions sleep, they can't be called from a timer. Luckily, timers aren't the only way to schedule work into the future. Look at work queues:

In particular, look at queue_delayed_work, which will allow you to run a function in the future, in a process context able to sleep.

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I implemented it using queue_delayed_work but the result is identical. The whole machine freezes every single case when execution reaches I2C communication.
For a sanity check, can you talk to the I2C device from userspace? Also, what happens if you try to do a read during the device probe.
I can use the device from both user and kernel space, if there is no timer / work queue. Even the I2C read/write in probe works, and everything is fine until the update function called by the timer / work queue.
The result after the timer / wq calls the update function is an oops: pastebin.com/JzDmDmuC
That's a simple null pointer dereference. Probably test114_i2c is null. Two things to try: printk the pointer value before using it, and be sure you initialise the variable before you queue the first work item.
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