On Wed, Jul 22, 2009 at 2:04 PM, Thomas Gleixner[off-list ref] wrote:

On Wed, 22 Jul 2009, David Brownell wrote:

quoted

On Wednesday 22 July 2009, Peter Zijlstra wrote:

quoted

Wouldn't it be better if we could express the nesting property from
within genirq, so that we can do things like:

  register_chip_nested(parent_chip, parent_irq, slave_chip);

And let genirq set-up the needed magic to make the nesting work.

I've been requesting such IRQ chaining support for some time
now ... if the ears are now listening, that kind of direction
should be pursued.

Well, I was all ear back then, but the disconnect between "embedded
only needs X be happy" and my repsonsibility to keep that all working
for everyone was way larger. :)

quoted

quoted

Also, how important is it that subhandler1..n run in their own thread?

Completely unimportant in a practical sense.  Undesirable, even;
wasteful to allocate all those stack pages and keep them idle
most of the time.

There might be an argument that the design isn't technicaly done
until that model *can* be supported.  On the flip side, last time
this came up there was no "customer demand" for that ... it was
all "supplier push".

quoted

That is, can't we let them run from the thread that is otherwise waiting
for the completino anyway?

That would be far preferable, yes.

Ok, so let me summarize what we came up with so far.

1) handle_level_oneshot_irq is the correct answer to the problem of
those "I'm behind a slow bus" interrupt controllers.

2) Some mechanism to request ONESHOT from the driver level is
required. Preferrably via a flag on request_threaded_irq

3) a function which allows to express the nested thread irq nature of
the interrupt controller and its subdevices.

4) a generic serializing mechanism which is implemented via irq_chip
functions to solve the chip->mask/unmask issue for the demultiplexed
interrupts. Something like the bus_lock/bus_sync_unlock patch I posted
earlier.

5) a common function which allows to call the thread handler of the
subdevice interrupts in the context of the main thread which takes
care of serialization against disable/enable/request/free irq et al.

Any more ?

It would also be useful to mask an edge triggered interrupt until the
thread handler has finished. The touchscreen on the G1 is connected to
an edge triggered interrupt, and the touchscreen may toggle the
interrupt line while reading its registers.

-- 
Arve Hjønnevåg