Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752520Ab1BAPTA (ORCPT ); Tue, 1 Feb 2011 10:19:00 -0500 Received: from metis.ext.pengutronix.de ([92.198.50.35]:35256 "EHLO metis.ext.pengutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751682Ab1BAPS7 (ORCPT ); Tue, 1 Feb 2011 10:18:59 -0500 Date: Tue, 1 Feb 2011 16:18:46 +0100 From: Uwe =?iso-8859-1?Q?Kleine-K=F6nig?= To: Russell King - ARM Linux Cc: Jeremy Kerr , Dima Zavin , Saravana Kannan , Lorenzo Pieralisi , linux-sh@vger.kernel.org, Ben Herrenschmidt , Sascha Hauer , linux-kernel@vger.kernel.org, Paul Mundt , Ben Dooks , Vincent Guittot , linux-arm-kernel@lists.infradead.org, Nicolas Pitre Subject: Re: Locking in the clk API, part 2: clk_prepare/clk_unprepare Message-ID: <20110201151846.GD1147@pengutronix.de> References: <201102011711.31258.jeremy.kerr@canonical.com> <20110201105449.GY1147@pengutronix.de> <20110201131512.GH31216@n2100.arm.linux.org.uk> <20110201141837.GA1147@pengutronix.de> <20110201143932.GK31216@n2100.arm.linux.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20110201143932.GK31216@n2100.arm.linux.org.uk> User-Agent: Mutt/1.5.20 (2009-06-14) X-SA-Exim-Connect-IP: 2001:6f8:1178:2:215:17ff:fe12:23b0 X-SA-Exim-Mail-From: ukl@pengutronix.de X-SA-Exim-Scanned: No (on metis.ext.pengutronix.de); SAEximRunCond expanded to false X-PTX-Original-Recipient: linux-kernel@vger.kernel.org Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1669 Lines: 41 On Tue, Feb 01, 2011 at 02:39:32PM +0000, Russell King - ARM Linux wrote: > On Tue, Feb 01, 2011 at 03:18:37PM +0100, Uwe Kleine-K?nig wrote: > > On Tue, Feb 01, 2011 at 01:15:12PM +0000, Russell King - ARM Linux wrote: > > > On Tue, Feb 01, 2011 at 11:54:49AM +0100, Uwe Kleine-K?nig wrote: > > > > 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's a completely bad idea. I assume you haven't thought about this > > > very much. > > Right, but I thought it a bit further than you did. Like the following: > > > > int clk_prepare(struct clk *clk) > > { > > int ret = 0, first; > > unsigned long flags; > > > > spin_lock_irqsave(&clk->enable_lock, flags); > > if (clk->flags & CLK_BUSY) { > > /* > > * this must not happen, please serialize calls to > > * clk_prepare/clk_enable > > */ > > How do different drivers serialize calls to clk_prepare? Are you > really suggesting that we should have a global mutex somewhere to > prevent this? yeah, didn't thought about multiple consumers, so (as Jeremy suggested) the right thing is to sleep until CLK_BUSY is cleared. Best regards Uwe -- Pengutronix e.K. | Uwe Kleine-K?nig | Industrial Linux Solutions | http://www.pengutronix.de/ | -- 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/