Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753988Ab3COJkN (ORCPT ); Fri, 15 Mar 2013 05:40:13 -0400 Received: from hqemgate03.nvidia.com ([216.228.121.140]:6694 "EHLO hqemgate03.nvidia.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753282Ab3COJkL (ORCPT ); Fri, 15 Mar 2013 05:40:11 -0400 X-PGP-Universal: processed; by hqnvupgp08.nvidia.com on Fri, 15 Mar 2013 02:33:07 -0700 Date: Fri, 15 Mar 2013 11:39:51 +0200 From: Peter De Schrijver To: Stephen Warren CC: Bill Huang , "mturquette@linaro.org" , "patches@linaro.org" , "linux-kernel@vger.kernel.org" , Russell King - ARM Linux , "linaro-dev@lists.linaro.org" , "linux-arm-kernel@lists.infradead.org" Subject: Re: [RFC 1/1] clk: Add notifier support in clk_prepare_enable/clk_disable_unprepare Message-ID: <20130315093951.GV18519@tbergstrom-lnx.Nvidia.com> References: <1363151317.3311.9.camel@bilhuang-vm1> <51400D9D.9060305@wwwdotorg.org> <1363153204.3311.14.camel@bilhuang-vm1> <5140C12A.4060900@wwwdotorg.org> <1363227311.3311.30.camel@bilhuang-vm1> <20130314092132.GE18519@tbergstrom-lnx.Nvidia.com> <1363253287.3311.32.camel@bilhuang-vm1> <51420EBB.7080503@wwwdotorg.org> <1363310454.3311.44.camel@bilhuang-vm1> <5142B027.4040403@wwwdotorg.org> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <5142B027.4040403@wwwdotorg.org> X-NVConfidentiality: public User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2326 Lines: 46 On Fri, Mar 15, 2013 at 06:22:47AM +0100, Stephen Warren wrote: > On 03/14/2013 07:20 PM, Bill Huang wrote: > > On Fri, 2013-03-15 at 01:54 +0800, Stephen Warren wrote: > >> On 03/14/2013 03:28 AM, Bill Huang wrote: > >>> On Thu, 2013-03-14 at 17:21 +0800, Peter De Schrijver wrote: > >>>> On Thu, Mar 14, 2013 at 03:15:11AM +0100, Bill Huang wrote: > >>>> > >>>>> I don't think deferring will work either, considering the usage of DVFS, > >>>>> device voltage is tightly coupled with frequency, when clock rate is > >>>>> about to increase, we have to boost voltage first and we can lower the > >>>>> voltage after the clock rate has decreased. All the above sequence have > >>>>> to be guaranteed or you might crash, so deferring not only make thing > >>>>> complicated in controlling the order but also hurt performance. > >>>> > >>>> But we could use notifiers in clk_prepare/clk_unprepare to set the voltage no? > >>>> As clk_prepare/clk_unprepare have to be called before clk_enable or after > >>>> clk_disable, the voltage can be raised to a safe level, before the clock > >>>> becomes active. > >>> > >>> Thanks Peter, actually I'm just about to propose my v2 RFC which add > >>> notifier in clk_prepare/clk_unprepare. > >> > >> Can't clk_set_rate() be called while the clock is prepared, or even > >> enabled? I don't see how your proposal would work. > > > > I think it works with just a little sacrifice on saving more power but > > that's related minor. Taking clk_prepare as an indicator on that clock > > will be enabled later, so we can raise the voltage to a safe level > > (according to the current rate or maybe default rate when clk_prepare is > > called, some time late when clk_set_rate() is called we can adjust again > > according to the requested rate change) > > Is clk_set_rate() only legal to call in non-atomic contexts then? The > header file doesn't say, although I guess since many other functions > explicitly say they can't, then by omission it can... Yes. Only clk_enable() and clk_disable() can be called in an atomic context. Cheers, Peter. -- 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/