From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760718AbaCULW2 (ORCPT ); Fri, 21 Mar 2014 07:22:28 -0400 Received: from mx07-00178001.pphosted.com ([62.209.51.94]:52757 "EHLO mx07-00178001.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1760658AbaCULW1 (ORCPT ); Fri, 21 Mar 2014 07:22:27 -0400 Message-ID: <532C206E.1020907@st.com> Date: Fri, 21 Mar 2014 12:20:14 +0100 From: Maxime Coquelin User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.3.0 MIME-Version: 1.0 To: Sylwester Nawrocki , , Cc: , , , , , , , , , , , , Subject: Re: [RFC PATCH v2 0/2] clk: Support for DT assigned clock parents and rates References: <1393870533-20845-1-git-send-email-s.nawrocki@samsung.com> <53187C13.3040202@st.com> <532AE239.9000800@samsung.com> In-Reply-To: <532AE239.9000800@samsung.com> Content-Type: text/plain; charset="ISO-8859-1"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [10.129.4.202] X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:5.11.87,1.0.14,0.0.0000 definitions=2014-03-21_03:2014-03-21,2014-03-21,1970-01-01 signatures=0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 03/20/2014 01:42 PM, Sylwester Nawrocki wrote: > Hi Maxime, > > On 06/03/14 14:45, Maxime Coquelin wrote: >> Hi Sylwester, >> >> I like the principle of your implementation, but I have two questions: >> 1 - How can we manage PM with this solution, as the parent/rate will be >> set only once at probe time? >> 2 - How to set the parent of a parent clock (which can be shared with >> other devices)? Same question about the parent rates. > > Thanks for your feedback and apologies for late reply. No problem! Apologies accepted ;) > > IIUC your first concern is about a situation when clocks need to be > reconfigured upon each resume from system sleep or runtime PM resume ? Yes. This is the case of the STi SoCs. When resuming from system sleep, the clocks-related registers are restored at their boot state. > As I mentioned in v1 of the RFC I was considering having individual > drivers calling explicitly the clocks set up routine. Presumably this > would allow to resolve the power management related issue. From a functional point of view, that would indeed resolve the PM related issue. But I'm not sure that on a performance point of view, parsing the DT at each driver's resume call is an efficient way. > One example I'm aware the approach as in this RFC wouldn't work is > when a device in a SoC belongs to a power domain, which needs to be > first switched on before we can start setting up and the clocks' > configuration get lost after the power domain switch off. Yes, that's another case to handle. I don't know which platforms are in that case, but not STi SoCs for your information. > > OTOH I suspect devices for which one-time clocks setup is sufficient > will be quite common. And for these there would need to be a single > call to the setup routine in probe() I guess, since it wouldn't be > possible to figure out just from the DT data when the actual call > should be made. > > For a global clocks configuration, I thought about specifying that > in the clocks controller node, and then to have the setup routine > called e.g. from of_clk_init(). I think that could work well enough, > together with the patch [1], adding clock dependencies handling. > But then the clock frequency set up function would need to be > modified to respect the clock parent relationships, similarly as > in patch series [2]. A just noticed [2] recently, after posting > this RFC (adding Tero at Cc). OK, I agree with the approach. There is still the PM issue remaining with these clocks, but I think that is not related to your series as we already have the issue currently. Thanks, Maxime > > -- > Regards, > Sylwester > > [1] http://www.spinics.net/lists/arm-kernel/msg310507.html > [2] http://www.spinics.net/lists/linux-omap/msg103069.html >