Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751840AbaJTRGM (ORCPT ); Mon, 20 Oct 2014 13:06:12 -0400 Received: from down.free-electrons.com ([37.187.137.238]:51383 "EHLO mail.free-electrons.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1750807AbaJTRGJ (ORCPT ); Mon, 20 Oct 2014 13:06:09 -0400 Date: Mon, 20 Oct 2014 19:06:04 +0200 From: Alexandre Belloni To: Vladimir Zapolskiy Cc: Thierry Reding , Maxime Ripard , jonsmirl@gmail.com, Simon , linux-pwm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCHv8 1/2] pwm: Add Allwinner SoC support Message-ID: <20141020170603.GG10616@piout.net> References: <1413743305-1979-1-git-send-email-alexandre.belloni@free-electrons.com> <1413743305-1979-2-git-send-email-alexandre.belloni@free-electrons.com> <54442BB1.1080403@mleia.com> <20141020102939.GB10616@piout.net> <544509C7.9010309@mleia.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <544509C7.9010309@mleia.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 20/10/2014 at 16:10:31 +0300, Vladimir Zapolskiy wrote : > Hi Alexandre, > > On 20.10.2014 13:29, Alexandre Belloni wrote: > > Hi, > > > > On 20/10/2014 at 00:22:57 +0300, Vladimir Zapolskiy wrote : > >>> +struct sun4i_pwm_chip { > >>> + struct pwm_chip chip; > >>> + struct clk *clk; > >>> + void __iomem *base; > >>> + struct mutex ctrl_lock; > >> > >> why do you use mutex? I haven't found any blocking subcalls under > >> protection, a spinlock seems to fit better here. > >> > > > > A mutex here will do the right thing. The lock is never taken in > > interrupt context and a mutex is spinning for a few cycles before > > putting the thread to sleep. > > and why do you want to put a thread to sleep in context of the driver? > Because the PWM is getting configured from either a kernel thread or a userspace thread accessing /sys. So you probably want the current thread to sleep so the other thread accessing the register can finish. Unless you are on smp and then, the mutex will spin for some time and your other cpu will be finished by then. -- Alexandre Belloni, Free Electrons Embedded Linux, Kernel and Android engineering http://free-electrons.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/