linux-kernel - Re: [PATCH try #3] Input/Joystick Driver: add support AD7142 joystick driver

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Date:	Mon, 15 Oct 2007 20:27:43 +0200
From:	"Ahmed S. Darwish" <darwish.07@...il.com>
To:	Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:	bryan.wu@...log.com, Andrey Panin <pazke@...pac.ru>,
	Roel Kluin <12o3l@...cali.nl>,
	linux-input@...ey.karlin.mff.cuni.cz,
	linux-joystick@...ey.karlin.mff.cuni.cz,
	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	Jean Delvare <khali@...ux-fr.org>
Subject: Re: [PATCH try #3] Input/Joystick Driver: add support AD7142 joystick driver

On Mon, Oct 15, 2007 at 11:48:17AM -0400, Dmitry Torokhov wrote:
> Hi Bryan,
> 
> On 10/15/07, Bryan Wu <bryan.wu@...log.com> wrote:
> > +
> > +static int ad7142_thread(void *nothing)
> > +{
> > +       do {
> > +               wait_for_completion(&ad7142_completion);
> > +               ad7142_decode();
> > +               enable_irq(CONFIG_BFIN_JOYSTICK_IRQ_PFX);
> > +       } while (!kthread_should_stop());
> > +
> 
> No, this is not going to work well:
> - you at least need to reinitialize the completion before enabling
> IRQ, otherwise you will spin in a very tight loop
> - if noone would touch the joystick ad7142_clsoe would() block
> infinitely because noone would signal the completion and
> ad7142_thread() would never stop.
> 
> Completion is just not a good abstraction here... Please use work
> abstraction and possibly a separate workqueue.
> 

Bryan, I'm very interested in the technical advantage of using a completion
here.

In my _not-experienced_ opinion, I remember completions was created mainly for
"create_task, wait till task got finished, go on" case. Why using it in a
different context while workqueues was created for a similar situation to
ad7142 one (non-irq context bottom-half) ?

Regards,

-- 
Ahmed S. Darwish
HomePage: http://darwish.07.googlepages.com
Blog: http://darwish-07.blogspot.com
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