From mboxrd@z Thu Jan 1 00:00:00 1970 From: Lorenzo Pieralisi Subject: Re: [PATCH 5/9] ARM: common: Introduce PM domains for CPUs/clusters Date: Thu, 13 Aug 2015 16:52:45 +0100 Message-ID: <20150813155245.GD13833@red-moon> References: <1438731339-58317-1-git-send-email-lina.iyer@linaro.org> <1438731339-58317-6-git-send-email-lina.iyer@linaro.org> <20150813150154.GB13356@red-moon> <20150813154503.GO52339@linaro.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from foss.arm.com ([217.140.101.70]:35489 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752135AbbHMPwl (ORCPT ); Thu, 13 Aug 2015 11:52:41 -0400 Content-Disposition: inline In-Reply-To: <20150813154503.GO52339@linaro.org> Sender: linux-pm-owner@vger.kernel.org List-Id: linux-pm@vger.kernel.org To: Lina Iyer Cc: Rob Herring , Rafael Wysocki , Ulf Hansson , Kevin Hilman , Mark Rutland , Krzysztof Koz??owski , "linux-pm@vger.kernel.org" , Catalin Marinas , Daniel Lezcano , Stephen Boyd , "msivasub@codeaurora.org" , Geert Uytterhoeven , Andy Gross , "linux-arm-kernel@lists.infradead.org" On Thu, Aug 13, 2015 at 04:45:03PM +0100, Lina Iyer wrote: > On Thu, Aug 13 2015 at 09:01 -0600, Lorenzo Pieralisi wrote: > >On Thu, Aug 06, 2015 at 04:14:51AM +0100, Rob Herring wrote: > >> On Tue, Aug 4, 2015 at 6:35 PM, Lina Iyer wrote: > >> > Define and add Generic PM domains (genpd) for ARM CPU clusters. Many new > >> > SoCs group CPUs as clusters. Clusters share common resources like GIC, > >> > power rail, caches, VFP, Coresight etc. When all CPUs in the cluster are > >> > idle, these shared resources may also be put in their idle state. > >> > > >> > The idle time between the last CPU entering idle and a CPU resuming > >> > execution is an opportunity for these shared resources to be powered > >> > down. Generic PM domain provides a framework for defining such power > >> > domains and attach devices to the domain. When the devices in the domain > >> > are idle at runtime, the domain would also be suspended and resumed > >> > before the first of the devices resume execution. > >> > > >> > We define a generic PM domain for each cluster and attach CPU devices in > >> > the cluster to that PM domain. The DT definitions for the SoC describe > >> > this relationship. Genpd callbacks for power_on and power_off can then > >> > be used to power up/down the shared resources for the domain. > >> > >> [...] > >> > >> > +ARM CPU Power domains > >> > + > >> > +The device tree allows describing of CPU power domains in a SoC. In ARM SoC, > >> > +CPUs may be grouped as clusters. A cluster may have CPUs, GIC, Coresight, > >> > +caches, VFP and power controller and other peripheral hardware. Generally, > >> > +when the CPUs in the cluster are idle/suspended, the shared resources may also > >> > +be suspended and resumed before any of the CPUs resume execution. > >> > + > >> > +CPUs are the defined as the PM domain consumers and there is a PM domain > >> > +provider for the CPUs. Bindings for generic PM domains (genpd) is described in > >> > +[1]. > >> > + > >> > +The ARM CPU PM domain follows the same binding convention as any generic PM > >> > +domain. Additional binding properties are - > >> > + > >> > +- compatible: > >> > + Usage: required > >> > + Value type: > >> > + Definition: Must also have > >> > + "arm,pd" > >> > + inorder to initialize the genpd provider as ARM CPU PM domain. > >> > >> A compatible string should represent a particular h/w block. If it is > >> generic, it should represent some sort of standard programming > >> interface (e.g, AHCI, EHCI, etc.). This doesn't seem to be either and > >> is rather just a mapping of what "driver" you want to use. > >> > >> I would expect that identifying a cpu's or cluster's power domain > >> would be done by a phandle between the cpu/cluster node and power > >> domain node. But I've not really looked at the power domain bindings > >> so who knows. > > > >I would expect the same, meaning that a cpu node, like any other device > >node would have a phandle pointing at the respective HW power domain. > > > CPUs have phandles to their domains. That is how the relationship > between the domain provider (power-controller) and the consumer (CPU) is > established. > > >I do not really understand why we want a "generic" CPU power domain, what > >purpose does it serve ? Creating a collection of cpu devices that we > >can call "cluster" ? > > > Nope, not for calling a cluster, a cluster :) > > This compatible is used to define a generic behavior of the CPU domain > controller (in addition to the platform specific behavior of the domain > power controller). The kernel activities for such power controller are > generally the same which otherwise would be repeated across platforms. What activities ? CPU PM notifiers ? Thanks, Lorenzo