Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753271Ab3COFWu (ORCPT ); Fri, 15 Mar 2013 01:22:50 -0400 Received: from avon.wwwdotorg.org ([70.85.31.133]:38568 "EHLO avon.wwwdotorg.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752894Ab3COFWs (ORCPT ); Fri, 15 Mar 2013 01:22:48 -0400 Message-ID: <5142B027.4040403@wwwdotorg.org> Date: Thu, 14 Mar 2013 23:22:47 -0600 From: Stephen Warren User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130221 Thunderbird/17.0.3 MIME-Version: 1.0 To: Bill Huang CC: Peter De Schrijver , "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 References: <1363091861-21534-1-git-send-email-bilhuang@nvidia.com> <20130312134032.GU4977@n2100.arm.linux.org.uk> <1363139273.21694.11.camel@bilhuang-vm1> <514003B6.8020904@wwwdotorg.org> <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> In-Reply-To: <1363310454.3311.44.camel@bilhuang-vm1> X-Enigmail-Version: 1.4.6 Content-Type: text/plain; charset=ISO-8859-9 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2099 Lines: 39 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... -- 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/