From mboxrd@z Thu Jan 1 00:00:00 1970 From: Brendan Jackman Subject: Re: [RFC/PATCH] dt: bindings: Define bindings for device idle states Date: Wed, 31 Aug 2016 16:04:02 +0100 Message-ID: <20160831150402.GA27374@brendan-thinkstation> References: <1472207073-4901-1-git-send-email-ulf.hansson@linaro.org> <20160831101644.GA2508@brendan-thinkstation> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Return-path: Received: from foss.arm.com ([217.140.101.70]:34884 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934880AbcHaPEI (ORCPT ); Wed, 31 Aug 2016 11:04:08 -0400 Content-Disposition: inline In-Reply-To: Sender: linux-pm-owner@vger.kernel.org List-Id: linux-pm@vger.kernel.org To: Ulf Hansson Cc: Rob Herring , Kevin Hilman , Lina Iyer , Sudeep Holla , Lorenzo Pieralisi , Daniel Lezcano , "devicetree@vger.kernel.org" , "Rafael J. Wysocki" , Len Brown , Pavel Machek , Geert Uytterhoeven , Axel Haslam , "linux-pm@vger.kernel.org" Hi, (I know I suggested switching to the other thread but I just want to explain my reasoning here!) On Wed, Aug 31, 2016 at 04:19:41PM +0200, Ulf Hansson wrote: > On 31 August 2016 at 12:16, Brendan Jackman wrote: [...] > > There was some previous discussion of whether device idle state bindings are > > necessary. It was proposed that rather than adding a whole new binding, we could > > just use the power domain idle state binding from [2]. We suggested that any > > device that has an idle state is, by definition, in a power domain of its own: > > rather than add a device-idle-states property to that device, we just put it in > > a power domain with a domain-idle-states property. > > Yes, we can do that software wise, but is that really a proper > description of the HW!? > It's probably not what SoC docs would explicitly list under "power domains" but I think "set of components that are bound by a common power state" is a reasonable definition for a power domain. I think (?) your objection is that a device could have idle states that it controls by itself and does not switch "off", for example in the case of a device that has an idle state where it gates its clock but does not cut voltage, or WFI in an ARM CPU. My thinking is: just because the transitions into those power states isn't triggered by a separate power controller, I don't think that means no "power domain" exists. Perhaps that's a glitch in my vocabulary.