Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753062Ab1BAPPd (ORCPT ); Tue, 1 Feb 2011 10:15:33 -0500 Received: from caramon.arm.linux.org.uk ([78.32.30.218]:44894 "EHLO caramon.arm.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751584Ab1BAPPb (ORCPT ); Tue, 1 Feb 2011 10:15:31 -0500 Date: Tue, 1 Feb 2011 15:14:18 +0000 From: Russell King - ARM Linux To: Uwe =?iso-8859-1?Q?Kleine-K=F6nig?= Cc: Jassi Brar , Jeremy Kerr , Nicolas Pitre , Lorenzo Pieralisi , linux-sh@vger.kernel.org, Ben Herrenschmidt , Sascha Hauer , Paul Mundt , linux-kernel@vger.kernel.org, Dima Zavin , Saravana Kannan , Ben Dooks , Vincent Guittot , linux-arm-kernel@lists.infradead.org Subject: Re: Locking in the clk API, part 2: clk_prepare/clk_unprepare Message-ID: <20110201151418.GN31216@n2100.arm.linux.org.uk> References: <201102011711.31258.jeremy.kerr@canonical.com> <20110201105449.GY1147@pengutronix.de> <20110201140024.GZ1147@pengutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20110201140024.GZ1147@pengutronix.de> User-Agent: Mutt/1.5.19 (2009-01-05) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1788 Lines: 37 On Tue, Feb 01, 2011 at 03:00:24PM +0100, Uwe Kleine-K?nig wrote: > On Tue, Feb 01, 2011 at 10:05:56PM +0900, Jassi Brar wrote: > > 2011/2/1 Uwe Kleine-K?nig : > > > > ..... > > > > > Do you plan to handle the case that clk_enable is called while prepare > > > isn't completed (considering the special case "not called at all")? > > > Maybe BUG_ON(clk->ops->prepare && !clk->prepare_count)? > > Sounds better than the second option. > > > > > Alternatively don't force the sleep in clk_prepare (e.g. by protecting > > > prepare_count by a spinlock (probably enable_lock)) and call clk_prepare > > > before calling clk->ops->enable? > > That might result in a driver working on some platforms(those have > > atomic clk_prepare) > > and not on others(those have sleeping). > The first option has the same result. E.g. on some platforms > clk->ops->prepare might be NULL, on others it's not. If clk->ops->prepare is NULL, then clk_prepare() better return success as it should mean "no preparation necessary", not "someone didn't implement it so its an error". Calling clk->ops->enable() with a spinlock held will ensure that no one tries to make that method sleep, so if people want sleeping stuff they have to use the clk_prepare() stuff. It's a self-enforcing API which ensures that we don't get sleeping stuff inside clk_enable(). And with a check in clk_enable() for a preparation, it helps to ensure that drivers do call clk_prepare() before clk_enable() - though it can't guarantee it in every case. -- 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/