Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754062Ab3COKIU (ORCPT ); Fri, 15 Mar 2013 06:08:20 -0400 Received: from mail-la0-f46.google.com ([209.85.215.46]:58304 "EHLO mail-la0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753282Ab3COKIT (ORCPT ); Fri, 15 Mar 2013 06:08:19 -0400 MIME-Version: 1.0 In-Reply-To: <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> <20130315093951.GV18519@tbergstrom-lnx.Nvidia.com> Date: Fri, 15 Mar 2013 11:08:17 +0100 Message-ID: Subject: Re: [RFC 1/1] clk: Add notifier support in clk_prepare_enable/clk_disable_unprepare From: Ulf Hansson To: Peter De Schrijver Cc: Stephen Warren , Russell King - ARM Linux , Bill Huang , "linux-kernel@vger.kernel.org" , "patches@linaro.org" , "linaro-dev@lists.linaro.org" , "linux-arm-kernel@lists.infradead.org" Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3364 Lines: 74 On 15 March 2013 10:39, Peter De Schrijver wrote: > 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. > > _______________________________________________ > linaro-dev mailing list > linaro-dev@lists.linaro.org > http://lists.linaro.org/mailman/listinfo/linaro-dev Just wanted to add my reflection on this topic; Some prerequisites; I think am in favor of using the clk API to trigger DVFS changes and then I agree on that clk_prepare|unprepare needs to be possible to track from a DVFS perspective. clk_set_rate is not enough. So if we decide to do the above (using the clk API to trigger DVFS changes), I believe we should discuss two possible solutions; - clk notifiers or.. - dvfs clock type. I am trying to make up my mind of what I think is the best solution. Have you considered "dvfs clock type"? I put some comments about this for "[PATCH 2/5] clk: notifier handler for dynamic voltage scaling" recently as well. What could the advantages/disadvantages be between the two options? Kind regards Ulf Hansson -- 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/