From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mika Westerberg Subject: Re: [PATCH v2] pwm: pca9685: fix pwm/gpio inter-operation Date: Wed, 5 Jun 2019 15:53:56 +0300 Message-ID: <20190605125356.GI2781@lahna.fi.intel.com> References: <20190604181345.9107-1-TheSven73@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20190604181345.9107-1-TheSven73@gmail.com> Sender: linux-kernel-owner@vger.kernel.org To: Sven Van Asbroeck Cc: Thierry Reding , linux-pwm@vger.kernel.org, linux-kernel@vger.kernel.org, Uwe =?iso-8859-1?Q?Kleine-K=F6nig?= , YueHaibing List-Id: linux-pwm@vger.kernel.org On Tue, Jun 04, 2019 at 02:13:45PM -0400, Sven Van Asbroeck wrote: > This driver allows pwms to be requested as gpios via gpiolib. > Obviously, it should not be allowed to request a gpio when its > corresponding pwm is already requested (and vice versa). > So it requires some exclusion code. > > Given that the pwm and gpio cores are not synchronized with > respect to each other, this exclusion code will also require > proper synchronization. > > Such a mechanism was in place, but was inadvertently removed > by Uwe's clean-up patch. > > Upon revisiting the synchronization mechanism, we found that > theoretically, it could allow two threads to successfully > request conflicting pwms / gpios. > > Replace with a bitmap which tracks pwm in-use, plus a mutex. > As long as pwm and gpio's respective request/free functions > modify the in-use bitmap while holding the mutex, proper > synchronization will be guaranteed. > > Reported-by: YueHaibing > Fixes: e926b12c611c ("pwm: Clear chip_data in pwm_put()") > Cc: Mika Westerberg Reviewed-by: Mika Westerberg