Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1764395AbXJPQlR (ORCPT ); Tue, 16 Oct 2007 12:41:17 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753227AbXJPQlF (ORCPT ); Tue, 16 Oct 2007 12:41:05 -0400 Received: from ug-out-1314.google.com ([66.249.92.171]:19438 "EHLO ug-out-1314.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753663AbXJPQlC (ORCPT ); Tue, 16 Oct 2007 12:41:02 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=beta; h=received:date:to:cc:subject:message-id:references:mime-version:content-type:content-disposition:in-reply-to:user-agent:from; b=c1wOBUbUGDW6paEd+pI3BP8NLP6R8Ftueo9QYIjCAxqnn4XaRLpvjK6qFT9ieroDLUwaDgiKPRJxWL2zgPnu+Yos/8icUwaA5zpb8uQ3P7TxVv+16WzghD+vWStjdZN6pq+Y7YawNd/7IJsQA6rsj9ZsmQc5br6tFHC1ZqcPwTg= Date: Tue, 16 Oct 2007 18:40:51 +0200 To: Bryan Wu Cc: Dmitry Torokhov , bryan.wu@analog.com, Andrey Panin , Roel Kluin <12o3l@tiscali.nl>, linux-input@atrey.karlin.mff.cuni.cz, linux-joystick@atrey.karlin.mff.cuni.cz, linux-kernel@vger.kernel.org, akpm@linux-foundation.org, Jean Delvare Subject: Re: [PATCH try #3] Input/Joystick Driver: add support AD7142 joystick driver Message-ID: <20071016164051.GC2528@Ahmed> References: <1192459625.6215.17.camel@roc-laptop> <20071015182743.GA2529@Ahmed> <386072610710152308o3d4a04bfgfcecafc9c345286b@mail.gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <386072610710152308o3d4a04bfgfcecafc9c345286b@mail.gmail.com> User-Agent: Mutt/1.5.11 From: "Ahmed S. Darwish" Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2903 Lines: 76 On Tue, Oct 16, 2007 at 02:08:04PM +0800, Bryan Wu wrote: > On 10/16/07, Ahmed S. Darwish wrote: > > On Mon, Oct 15, 2007 at 11:48:17AM -0400, Dmitry Torokhov wrote: > > > Hi Bryan, > > > > > > On 10/15/07, Bryan Wu 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. > > > You are welcome, I'd like to discuss these things 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) ? > > I like completion because it is simple to use and understand. Your > understanding is right. But there is no limit for using different > context with completion. completion is a wrapper of waitqueue+done > flag. For some drivers, in process context call > wait_for_completetion(), then schedule out and in irq handler call > complete(). This is very simple and helpful for driver design (For > example, you call dma function to transfer data, then you schedule out > and then DMA IRQ handler will call complete() to wakeup you). > Thank you for such a useful information. > But in this driver, a) can not call ad7142_decode() in IRQ handler, > because it will sleep in IRQ context by calling some i2c API, b) in > original design, creating a new kthread and using some waitqueue API > is the same way as using workqueue, c) cannot use completion as Dmitry > said. > > I am going to use workqueue here. > > Any idea? > I have no better thoughts than the ones provided by Dmitry actually. > Thanks > -Bryan Wu Regards :), -- Ahmed S. Darwish HomePage: http://darwish.07.googlepages.com Blog: http://darwish-07.blogspot.com - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/