Date: Wed, 22 Jul 2009 23:04:33 +0200 (CEST)
From: Thomas Gleixner <tglx@linutronix.de>
To: David Brownell <david-b@pacbell.net>
cc: Peter Zijlstra <peterz@infradead.org>,
       Mark Brown <broonie@opensource.wolfsonmicro.com>,
       Dmitry Torokhov <dmitry.torokhov@gmail.com>,
       Trilok Soni <soni.trilok@gmail.com>, Pavel Machek <pavel@ucw.cz>,
       Arve Hj?nnev?g <arve@android.com>,
       kernel list <linux-kernel@vger.kernel.org>,
       Brian Swetland <swetland@google.com>, linux-input@vger.kernel.org,
       Andrew Morton <akpm@osdl.org>, linux-i2c@vger.kernel.org,
       Joonyoung Shim <jy0922.shim@samsung.com>, m.szyprowski@samsung.com,
       t.fujak@samsung.com, kyungmin.park@samsung.com,
       Daniel Ribeiro <drwyrm@gmail.com>
Subject: Re: Threaded interrupts for synaptic touchscreen in HTC dream
In-Reply-To: <200907220957.16499.david-b@pacbell.net>
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On Wed, 22 Jul 2009, David Brownell wrote:
> On Wednesday 22 July 2009, Peter Zijlstra wrote:
> > 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. :)

> > 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".
> 
> 
> > 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 ?

Thanks,

	tglx
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