linux-kernel - Re: Threaded interrupts for synaptic touchscreen in HTC dream

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Message-Id: <200907220951.54419.david-b@pacbell.net>
Date:	Wed, 22 Jul 2009 09:51:53 -0700
From:	David Brownell <david-b@...bell.net>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Trilok Soni <soni.trilok@...il.com>,
	Pavel Machek <pavel@....cz>,
	"Arve Hj?nnev?g" <arve@...roid.com>,
	kernel list <linux-kernel@...r.kernel.org>,
	Brian Swetland <swetland@...gle.com>,
	linux-input@...r.kernel.org, Andrew Morton <akpm@...l.org>,
	linux-i2c@...r.kernel.org,
	Joonyoung Shim <jy0922.shim@...sung.com>,
	m.szyprowski@...sung.com, t.fujak@...sung.com,
	kyungmin.park@...sung.com, Peter Zijlstra <peterz@...radead.org>,
	Daniel Ribeiro <drwyrm@...il.com>
Subject: Re: Threaded interrupts for synaptic touchscreen in HTC dream

On Wednesday 22 July 2009, Thomas Gleixner wrote:
> main interrupt
>      hardirq handler wakes main thread handler
> 
> main thread handler
>     bus magic
>         subdevice1 "hardirq" handler wakes subdevice1 irq thread
>         subdevice2 "hardirq" handler wakes subdevice2 irq thread

Why force this wasteful/undesired "all subdevices must
have their own IRQ handling thread" policy?

As previously noted, a single thread typically suffices.
There's no need to waste a dozen (or so) pages of memory
for such purposes ... these events are (as noted most
recently by Mark) infrequent/rare and performance isn't
a functionality gatekeeper.  Plus ...


>     main thread handler waits for subdevice1/2 handlers to complete

... sharing that thread can eliminate that synchronization
problem, and simplify the whole process.


> subdevice1 thread handler
>     bus magic
>     ....
>     thread_fn returns
>     signal main thread handler via completion
> 
> subdevice2 thread handler
>     bus magic
>     ....
>     thread_fn returns
>     signal main thread handler via completion
> 
> main thread handler resumes
>     bus magic
>     main thread handler returns from thread_fn
>     unmask main interrupt


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