HELP PLEASE: i2c in interrupt?

[Abraham vd Merwe <abz@frogfoot.net>]

Hi!

I'm working on a keypad driver which is sitting on an I/O expander on an I2C
bus. Whenever a key is pressed, the I2C chip (the I/O expander) generates an
interrupt and then I have to read the events from the I2C chip.

The problem is

 (a) This operation is time critical. If I don't read the data from the I2C
     chip very fast (after the interrupt occurred) the events get lost

 (b) I2C is done in hardware which means a read goes like this: START
     WRITE_DATA wait_for_interrupt ... STOP.

The important part here is the wait_for_interrupt. That means i2c_transfer()
will wait on a wait queue which I can't do from an interupt so I created a
task to do this for me and from the keypad interrupt routine, I do 

        queue_task (&keypad.task,&tq_immediate);
        mark_bh (IMMEDIATE_BH);

However that triggers a BUG

------------< snip <------< snip <------< snip <------------
Scheduling in interrupt
kernel BUG at sched.c:566!
Unable to handle kernel NULL pointer dereference at virtual address 00000000
------------< snip <------< snip <------< snip <------------

so it is obviously illegal to do that from an interrupt. So my question is,
how do I execute a function which will sleep _very_soon_ after an interrupt
occurs (i.e. what I don't want to do is interrupt -> poll wakes up ->
process does read -> i2c_transfer() - that's too long)

-- 

Regards
 Abraham

You will not be elected to public office this year.

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 Abraham vd Merwe - Frogfoot Networks CC
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