From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753003Ab2I0OIb (ORCPT ); Thu, 27 Sep 2012 10:08:31 -0400 Received: from lxorguk.ukuu.org.uk ([81.2.110.251]:46322 "EHLO lxorguk.ukuu.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751375Ab2I0OI3 (ORCPT ); Thu, 27 Sep 2012 10:08:29 -0400 Date: Thu, 27 Sep 2012 15:13:14 +0100 From: Alan Cox To: Davide Ciminaghi Cc: Mark Brown , sameo@linux.intel.com, rubini@gnudd.com, giancarlo.asnaghi@st.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/8] sta2x11-mfd : add apb-soc regs driver and factor out common code Message-ID: <20120927151314.118c86c1@pyramind.ukuu.org.uk> In-Reply-To: <20120927134110.GD6799@mail.gnudd.com> References: <1347445374-32140-1-git-send-email-ciminaghi@gnudd.com> <1347445374-32140-2-git-send-email-ciminaghi@gnudd.com> <20120925192048.GA17038@sirena.org.uk> <20120926145615.GJ10147@mail.gnudd.com> <20120926150429.GQ4428@opensource.wolfsonmicro.com> <20120926163145.GK10147@mail.gnudd.com> <20120926164932.GS4428@opensource.wolfsonmicro.com> <20120927134110.GD6799@mail.gnudd.com> X-Mailer: Claws Mail 3.8.1 (GTK+ 2.24.8; x86_64-redhat-linux-gnu) Face: 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 Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > as far as I know, nested locks are fine provided that you always take them in > the same order and release them in the opposite order (lock A, lock B, > unlock B, unlock A). So my conclusion is that nested spinlocks require > potential regmap users of sta2x11 registers to take the sta2x11-mfd spinlock > first. The pattern would be (sctl registers for instance): The release order does not matter. Taking AB and releasing AB or BA is fine. Taking AB and dropping B and retaking B is fine. Taking AB and somewhere else taking BA is not. There are performance reasons in some cases why taking AB releasing A is best with locks, but thats generally with sleepable locks. It's a bit more subtle because you often have other interactions. In particular people often come unstuck on del_timer_sync or waiting for workqueues and IRQs to finish (even in free_irq) while holding a lock that the handler needs to take. Alan