From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753802AbcGDNm0 (ORCPT ); Mon, 4 Jul 2016 09:42:26 -0400 Received: from foss.arm.com ([217.140.101.70]:47650 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753262AbcGDNmX (ORCPT ); Mon, 4 Jul 2016 09:42:23 -0400 Subject: Re: [PATCH v7 2/6] ACPI / processor_idle: Add support for Low Power Idle(LPI) states To: "Rafael J. Wysocki" References: <1467122152-5604-1-git-send-email-sudeep.holla@arm.com> <57766B15.4090407@linaro.org> <577A5DD3.4050901@arm.com> <6955030.D47pi9uhTn@vostro.rjw.lan> Cc: Sudeep Holla , Daniel Lezcano , linux-acpi@vger.kernel.org, Vikas Sajjan , Sunil , Lorenzo Pieralisi , PrashanthPrakash , Al Stone , Ashwin Chaugule , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Vincent Guittot From: Sudeep Holla Organization: ARM Message-ID: <577A67BA.8060709@arm.com> Date: Mon, 4 Jul 2016 14:42:18 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.8.0 MIME-Version: 1.0 In-Reply-To: <6955030.D47pi9uhTn@vostro.rjw.lan> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 04/07/16 14:17, Rafael J. Wysocki wrote: > On Monday, July 04, 2016 02:00:03 PM Sudeep Holla wrote: >> >> On 01/07/16 14:07, Daniel Lezcano wrote: >>> On 06/28/2016 03:55 PM, Sudeep Holla wrote: >>>> ACPI 6.0 introduced an optional object _LPI that provides an alternate >>>> method to describe Low Power Idle states. It defines the local power >>>> states for each node in a hierarchical processor topology. The OSPM can >>>> use _LPI object to select a local power state for each level of processor >>>> hierarchy in the system. They used to produce a composite power state >>>> request that is presented to the platform by the OSPM. >>>> >>>> Since multiple processors affect the idle state for any non-leaf >>>> hierarchy >>>> node, coordination of idle state requests between the processors is >>>> required. ACPI supports two different coordination schemes: Platform >>>> coordinated and OS initiated. >>>> >>>> This patch adds initial support for Platform coordination scheme of LPI. >>>> >>>> Cc: "Rafael J. Wysocki" >>>> Signed-off-by: Sudeep Holla >>>> --- >>> >>> Hi Sudeep, >>> >>> I looked at the acpi processor idle code sometime ago and from my POV, >>> it was awful, unnecessary complex and very difficult to maintain. The >>> usage of flags all over the places is significant of the lack of control >>> of the written code. >>> >> >> So you have any specific things in mind ? That's too broad and I know >> it's not so clean, but it's so for legacy reasons. I would leave that >> to Rafael to decide as it takes lots of testing to clean up these code. > > The cleanup needs to be done at one point. > > Question is when to do it, before adding LPI support or after doing that > (and each option has its pros and cons IMO). > >>> Even if you are not responsible of this implementation, the current >>> situation forces you to add more awful code on top of that, which is >>> clearly against "making Linux better". >>> >> >> OK > > So if there are cases in which you need to make the code more complex > because of the legacy stuff in there, I'd say it's better to clean it up > first. > I am not sure if Daniel was referring to anything specific. I have cleaned up in patch 1/6 for cstate. More cleanups can be done there but needs better understanding and reasoning for the current code which I don't have as they are mostly x86 related. Unless someone points me what they would like to change and how, I don't have much in my mind to do here. Yes it may not look as clean as other code in the kernel relatively, but without complete understanding of the history/reasoning for the current state of code I wouldn't touch anything I don't understand. I am open to make changes if there's something specific. Sorry I can't go ahead making changes the way I think based on some vague idea that the current code is not clean. -- Regards, Sudeep