Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752006Ab3CRKgd (ORCPT ); Mon, 18 Mar 2013 06:36:33 -0400 Received: from mail-lb0-f172.google.com ([209.85.217.172]:61564 "EHLO mail-lb0-f172.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751858Ab3CRKgb (ORCPT ); Mon, 18 Mar 2013 06:36:31 -0400 MIME-Version: 1.0 In-Reply-To: <514378CB.1060605@wwwdotorg.org> 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> <1363349206.5827.10.camel@bilhuang-vm1> <514378CB.1060605@wwwdotorg.org> Date: Mon, 18 Mar 2013 11:36:29 +0100 Message-ID: Subject: Re: [RFC 1/1] clk: Add notifier support in clk_prepare_enable/clk_disable_unprepare From: Ulf Hansson To: Stephen Warren Cc: Bill Huang , Peter De Schrijver , Russell King - ARM Linux , "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: 3242 Lines: 65 On 15 March 2013 20:38, Stephen Warren wrote: > On 03/15/2013 06:33 AM, Ulf Hansson wrote: >> On 15 March 2013 13:06, Bill Huang wrote: >>> On Fri, 2013-03-15 at 18:08 +0800, Ulf Hansson wrote: > ... >>>> 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? >>> >>> I personally prefer clk notifiers since that's easy and all the existing >>> device drivers don't need to be modified, a new clock or API might be >>> more thoroughly considered (and hence maybe more graceful) but that >>> means we need more time to cook and many drivers need to plug into that >>> API when it comes out, a lot of test/verification or maybe chaos >>> follows, I'm not sure will that be a little overkill. >> >> I guess you did not fully got what I meant with "dvfs clock type". It >> will not affect the clock API. But instead the dvfs is handled by >> implementing a specific clk hw type. So the same thing is accomplished >> as with clk notifiers, no changes should be needed to device drivers. >> >> The difference is only that no notifiers will be needed, and all the >> dvfs stuff will be handled in the clk hw instead. It will mean that we >> will bundle dvfs stuff into the clock drivers, instead of separating >> the code outside the clock drivers. But, on the other hand no >> notifiers will be needed. > > The advantage here is that I assume that a notifier would continually > have to check whether the clock being modified was one that the DVFS > notifier cared about. By integrating the CVFS logic into the clk_hw > itself, it'll only ever get executed for clocks that really care about > DVFS. Presumably, the code that implements the clk_hw could also use > some common DVFS library as part of the implementation, and still share > code. Or perhaps, what about putting DVFS "ops" into a clk_hw alongside > any other existing ops, and having the clock core call them whenever > appropriate? Thanks for your comment Stephen. I agree to your reflections as well. It will probably be a more optimized solution going this direction and we don't have to add more "clk notifier code" to the clk API, which I guess is good. It would be interesting to get some input from some of the maintainers to this discussion as well, let's see. 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/