David Brownell wrote:

The other is that Linux needs real support for threaded
interrupts.  Almost every I2C (or SPI) device that raises
an IRQ needs its IRQ handler to run in a thread, and most
of them have the same type of workqueue-based hack to
get such a thread.  (Some others have bugs instead...)

Since when is having an IRQ handler scheduling a workqueue job a hack?
In kernels whose IRQ handlers don't sleep, we don't pretend that they
could; instead we defer sleeping work to a context which can sleep.

Or from another angle:  If a driver requires a kernel with sleeping IRQ
handlers, why submit it for inclusion into a kernel which does not
provide nonatomic context to IRQ handlers?
-- 
Stefan Richter
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http://arcgraph.de/sr/