From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dmitry Torokhov Subject: Re: [PATCH v2] Input: ads7846 - Replace spinlock by mutex to wrap disable()/enable() Date: Wed, 1 Sep 2010 09:48:18 -0700 Message-ID: <20100901164818.GA6908@core.coreip.homeip.net> References: <1282370340-3157-1-git-send-email-jason77.wang@gmail.com> <4C7491D7.1030801@gmail.com> <20100901064841.GH23585@core.coreip.homeip.net> <4C7E25E2.90904@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from mail-pw0-f46.google.com ([209.85.160.46]:49326 "EHLO mail-pw0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752743Ab0IAQsY (ORCPT ); Wed, 1 Sep 2010 12:48:24 -0400 Received: by pwi3 with SMTP id 3so844618pwi.19 for ; Wed, 01 Sep 2010 09:48:23 -0700 (PDT) Content-Disposition: inline In-Reply-To: <4C7E25E2.90904@gmail.com> Sender: linux-input-owner@vger.kernel.org List-Id: linux-input@vger.kernel.org To: Jason Wang Cc: notasas@gmail.com, vapier@gentoo.org, linux-input@vger.kernel.org On Wed, Sep 01, 2010 at 06:07:30PM +0800, Jason Wang wrote: > Dmitry Torokhov wrote: > >Hi Jason, > > > >On Wed, Aug 25, 2010 at 11:45:27AM +0800, Jason Wang wrote: > >>Hi dmitry and others, > >> > >>could you please to help me review this patch? > >> > >>Thanks, > >>Jason. > >> > >>Jason Wang wrote: > >>>The commit 9114337 introduces regulator operations in the ads7846 > >>>touchscreen driver. Among these operations, some are called in the > >>>spinlock protected context. > >>>On most platforms, the regulator operation is achieved through > >>>i2c/spi bus transfer operations, some bus transfer operations will > >>>call wait_for_completion function. It isn't allowable to call > >>>sleepable function in the atomic context. So replace the spinlock with > >>>mutex to protect ads7846_disable()/ads7846_enable(). > >>> > > > >I am afraid the patch is not correct. ads7846_disable() and > >ads7846_enable() check and modify flags (such as irq_disabled and > >pending) that are also accessed form timer/interrupt context. Moving to > >mutex removes the serialization that used to be there. > Thanks for your comments. you are right it is dangerous and > unreasonable to use different locks to protect a critical resource. > >I wonder if we should start by converting the driver to used threaded > >IRQ model with "long playing" interrupt handler so all access happens in > >process context and shutdown sequence is simplified. > It can solve most issues, but it can't solve this situation. Because > here the atomic region in which conflicts happened is from spin_lock > instead of irq handler. > Right, but switching to threaded IRQ will allow to use mutex in place of the spinlock everywhere. -- Dmitry