Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755702Ab3CNJV4 (ORCPT ); Thu, 14 Mar 2013 05:21:56 -0400 Received: from hqemgate04.nvidia.com ([216.228.121.35]:11201 "EHLO hqemgate04.nvidia.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751037Ab3CNJVz (ORCPT ); Thu, 14 Mar 2013 05:21:55 -0400 X-PGP-Universal: processed; by hqnvupgp07.nvidia.com on Thu, 14 Mar 2013 02:21:35 -0700 Date: Thu, 14 Mar 2013 11:21:32 +0200 From: Peter De Schrijver To: Bill Huang CC: Stephen Warren , "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: <20130314092132.GE18519@tbergstrom-lnx.Nvidia.com> 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> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <1363227311.3311.30.camel@bilhuang-vm1> 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: 997 Lines: 22 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. 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/