From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752237AbdEBKMY (ORCPT ); Tue, 2 May 2017 06:12:24 -0400 Received: from hqemgate16.nvidia.com ([216.228.121.65]:4882 "EHLO hqemgate16.nvidia.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752106AbdEBKMT (ORCPT ); Tue, 2 May 2017 06:12:19 -0400 X-PGP-Universal: processed; by hqpgpgate101.nvidia.com on Tue, 02 May 2017 03:12:13 -0700 Subject: Re: [RFC PATCH 0/4] PM / Domains: Add support for explicit control of PM domains To: "Rafael J. Wysocki" , Ulf Hansson References: <1490710443-27425-1-git-send-email-jonathanh@nvidia.com> CC: "Rafael J . Wysocki" , Kevin Hilman , Geert Uytterhoeven , "Rajendra Nayak" , Stanimir Varbanov , Stephen Boyd , "Marek Szyprowski" , "linux-pm@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "linux-tegra@vger.kernel.org" From: Jon Hunter Message-ID: Date: Tue, 2 May 2017 11:10:29 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.8.0 MIME-Version: 1.0 In-Reply-To: X-Originating-IP: [10.21.132.162] X-ClientProxiedBy: UKMAIL101.nvidia.com (10.26.138.13) To UKMAIL101.nvidia.com (10.26.138.13) Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 25/04/17 22:17, Rafael J. Wysocki wrote: > On Tue, Apr 25, 2017 at 9:34 PM, Ulf Hansson wrote: >> On 25 April 2017 at 13:13, Jon Hunter wrote: >>> >>> On 28/03/17 15:13, Jon Hunter wrote: >>>> The current generic PM domain framework (GenDP) only allows a single >>>> PM domain to be associated with a given device. There are several >>>> use-cases for various system-on-chip devices where it is necessary for >>>> a PM domain consumer to control more than one PM domain where the PM >>>> domains: >>>> i). Do not conform to a parent-child relationship so are not nested >>>> ii). May not be powered on and off at the same time so need independent >>>> control. >>>> >>>> The solution proposed in this RFC is to allow consumers to explictly >>>> control PM domains, by getting a handle to a PM domain and explicitly >>>> making calls to power on and off the PM domain. Note that referencing >>>> counting is used to ensure that a PM domain shared between consumers >>>> is not powered off incorrectly. >>>> >>>> The Tegra124/210 XUSB subsystem (that consists of both host and device >>>> controllers) is an example of a consumer that needs to control more than >>>> one PM domain because the logic is partitioned across 3 PM domains which >>>> are: >>>> - XUSBA: Superspeed logic (for USB 3.0) >>>> - XUSBB: Device controller >>>> - XUSBC: Host controller >>>> >>>> These power domains are not nested and can be powered-up and down >>>> independently of one another. In practice different scenarios require >>>> different combinations of the power domains, for example: >>>> - Superspeed host: XUSBA and XUSBC >>>> - Superspeed device: XUSBA and XUSBB >>>> >>>> Although it could be possible to logically nest both the XUSBB and XUSBC >>>> domains under the XUSBA, superspeed may not always be used/required and >>>> so this would keep it on unnecessarily. >>>> >>>> Given that Tegra uses device-tree for describing the hardware, it would >>>> be ideal that the device-tree 'power-domains' property for generic PM >>>> domains could be extended to allow more than one PM domain to be >>>> specified. For example, define the following the Tegra210 xHCI device ... >>>> >>>> usb@70090000 { >>>> compatible = "nvidia,tegra210-xusb"; >>>> ... >>>> power-domains = <&pd_xusbhost>, <&pd_xusbss>; >>>> power-domain-names = "host", "superspeed"; >>>> }; >>>> >>>> This RFC extends the generic PM domain framework to allow a device to >>>> define more than one PM domain in the device-tree 'power-domains' >>>> property. If there is more than one then the assumption is that these >>>> PM domains will be controlled explicitly by the consumer and the device >>>> will not be automatically bound to any PM domain. >>> >>> Any more comments/inputs on this? I can address Rajendra's feedback, but >>> before I did I wanted to see if this is along the right lines or not? >> >> I discussed this with Rafael at the OSPM summit in Pisa a couple of >> weeks ago. Apologize for the delay in providing additional feedback. >> >> First, whether the problem is really rare, perhaps adding a new >> API/framework can't be justified - then it may be better to add some >> kind of aggregation layer on top of the current PM domain >> infrastructure (something along the first attempt you made for genpd). >> That was kind of Rafael's thoughts (Rafael, please correct me if I am >> wrong). > > We were talking about the original idea behind the pm_domain pointer > concept, which was about adding a set of PM operations above the bus > type/class layer, which could be used for intercepting bus-type PM > operations and providing some common handling above them. This is > still relevant IMO. > > The basic observation here is that the PM core takes only one set of > PM operation per device into account and therefore, in every stage of > system suspend, for example, the callback invoked by it has to take > care of all actions that need to be carried out for the given device, > possibly by invoking callbacks from other code layers. That > limitation cannot be removed easily, because it is built into the PM > core design quite fundamentally. > > However, this series seems to be about controlling power resources > represented by power domain objects rather than about PM operations. > In ACPI there is a power resource concept which seems to be quite > similar to this, so it is not entirely new. :-) > > Of course, question is whether or not to extend genpd this way and I'm > not really sure. I actually probably wouldn't do that, because > poweron/poweroff operations used by genpd can be implemeted in terms > of lower-level power resource control and I don't see the reason for > mixing the two in one framework. That seems fine to me. However, it seems that genpd itself should also be a client of this 'low-level power resource control' so that power-domains are registered once and can be used by either method. So unless I am misunderstanding you here, it seems that what we need to do is split the current genpd framework into a couple layers: 1. Low-level power resource control which has: - Power resource registration (ie. pm_genpd_init/remove()) - Power resource provider registration (ie. of_genpd_add_xxx()) - Power resource control (on/off etc) - Power resource lookup (what this series is adding) 2. Generic power-domain infrastructure which is a client of the low-level power resource control that can automatically bind a device to a singular power resource entity (ie. power-domain). Is this along the right lines? Cheers Jon -- nvpublic