RFC Support for irq chips on slow busses (i2c, spi)

The support for irq chips on slow busses eg. i2c, spi has been discussed to great length several times. Most of the details can be found in this thread: http://lkml.org/lkml/2009/7/21/266

The following patch series is a round up of the various patch snippets sent out during the discussion and the ideas we agreed on.

There are some subtle differences to the initial test patches:

1) Instead of using a separate flow handler we allow to request the one shot feature with a flag on request_irq and integrate the oneshot feature into the existing level/edge handlers.

2) Instead of conditional locking which makes the patch smaller but hides the already known fact that a device sits behind a slow irq chip I implemented a set of separate management functions (see patch 2/3). The initial idea with the conditional locking can be found here:
http://lkml.org/lkml/2009/7/22/163

3) patch 3/3 implements a helper function which allows the demultiplexing thread to call the demux handlers in its own thread context with out creating a separate thread for each subdevice interrupt. The device driver needs to request the interrupt via request_nested_slowbus_irq() to prevent the creation of the extra thread.

Please have a thorough look and hopefully a test ride on your favourite slowbus irq chip implementation so we can get this into .32

Thanks,

tglx