Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S938389AbcKWNPr (ORCPT ); Wed, 23 Nov 2016 08:15:47 -0500 Received: from mail-wj0-f193.google.com ([209.85.210.193]:36841 "EHLO mail-wj0-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S936360AbcKWNPn (ORCPT ); Wed, 23 Nov 2016 08:15:43 -0500 MIME-Version: 1.0 In-Reply-To: <82802459-8292-efb7-ac23-733de8687d51@nvidia.com> References: <1474367287-10402-1-git-send-email-jonathanh@nvidia.com> <90faea7d-65b6-590a-83f1-24fcdffa0569@nvidia.com> <63670abf-1d58-a7e3-6927-0c815d44d8a1@nvidia.com> <82802459-8292-efb7-ac23-733de8687d51@nvidia.com> From: "Rafael J. Wysocki" Date: Wed, 23 Nov 2016 14:15:40 +0100 X-Google-Sender-Auth: 2HUXK2NRg5td1DXuRRrGfkZoRJA Message-ID: Subject: Re: [RFC PATCH 0/3] PM / Domains: Add support for devices that require multiple domains To: Jon Hunter Cc: "Rafael J. Wysocki" , Kevin Hilman , Ulf Hansson , "Rafael J. Wysocki" , "linux-pm@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "linux-tegra@vger.kernel.org" , Rajendra Nayak Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5278 Lines: 110 On Wed, Nov 23, 2016 at 10:29 AM, Jon Hunter wrote: > > On 22/11/16 21:55, Rafael J. Wysocki wrote: >> On Tue, Nov 22, 2016 at 7:26 PM, Kevin Hilman wrote: >>> Jon Hunter writes: >>> >>>> On 16/11/16 12:53, Rafael J. Wysocki wrote: >>>>> On Wed, Nov 16, 2016 at 11:48 AM, Jon Hunter wrote: >>>>>> Hi Kevin, Ulf, >>>>>> >>>>>> On 03/11/16 14:20, Jon Hunter wrote: >>>>>>> >>>>>>> On 11/10/16 10:15, Jon Hunter wrote: >>>>>>> >>>>>>> ... >>>>>>> >>>>>>>>>>> Second, another way of seeing this is: Depending on the current >>>>>>>>>>> runtime selected configuration you need to re-configure the PM domain >>>>>>>>>>> topology - but the device would still remain in the same PM domain. >>>>>>>>>>> >>>>>>>>>>> In other words, you would need to remove/add subdomain(s) depending on >>>>>>>>>>> the selected configuration. Would that better reflect the HW? >>>>>>>>>> >>>>>>>>>> I am not 100% sure I follow what you are saying, but ultimately, I would >>>>>>>>>> like to get to ... >>>>>>>>>> >>>>>>>>>> usb@70090000 { >>>>>>>>>> compatible = "nvidia,tegra210-xusb"; >>>>>>>>>> ... >>>>>>>>>> power-domains = <&pd_xusbhost>, <&pd_xusbss>; >>>>>>>>>> }; >>>>>>>>> >>>>>>>>> So, is this really is a proper description of the HW? Isn't it so, >>>>>>>>> that the usb device always resides in one and the same PM domain? >>>>>>>> >>>>>>>> I guess technically, the usbhost controller resides in one partition and >>>>>>>> the super-speed logic in another. So could the usbhost domain be the >>>>>>>> primary? Possibly, but the device cannot be probed without both enabled. >>>>>>>> >>>>>>>>> Now, depending on the selected speed mode (superspeed) additional >>>>>>>>> logic may needs to be powered on and configured for the usb device to >>>>>>>>> work? >>>>>>>>> Perhaps, one could consider those additional logics as a master/parent >>>>>>>>> PM domain for the usb device's PM domain? >>>>>>>>> >>>>>>>>> Or this is not how the HW works? :-) >>>>>>>> >>>>>>>> It might be possible for this case, but to be honest, the more I think >>>>>>>> about this, I do wonder if we need to be able to make the framework a >>>>>>>> lot more flexible for devices that need multiple power-domains. In other >>>>>>>> words, for devices that use multiple domains allow them to control them >>>>>>>> similarly to what we do for regulators or clocks. So if there is more >>>>>>>> than one defined, then the genpd core will not bind the device to the >>>>>>>> pm-domain and let the driver handle it. This way if you do need more >>>>>>>> granular control of the pm-domains in the driver you can do whatever you >>>>>>>> need to. >>>>>>>> >>>>>>>> I know that Rajendra (CC'ed) was looking into whether he had a need to >>>>>>>> control multiple power-domains individually from within the context of a >>>>>>>> single device driver. >>>>>>> >>>>>>> So Rajendra commented to say that he does not see a need for individual >>>>>>> control of power-domains for now, but a need for specifying multiple. >>>>>>> >>>>>>> One simple option would be to allow users to specify multiple and have >>>>>>> the genpd core effectively ignore such devices and leave it to the >>>>>>> driver to configure manually. I have been able to do this for XUSB by >>>>>>> dynamically adding power-domains to the device. >>>>>>> >>>>>>> Let me know if you have any more thoughts on how we can do this. >>>>>> >>>>>> Any more thoughts on this? Seems that there are a few others that would >>>>>> be interested in supporting multiple domains for a device. >>>>> >>>>> There is a design limitation to that, however. >>>>> >>>>> The PM domain concept really is about intercepting the flow of PM >>>>> callbacks for a device in order to carry out additional operations, >>>>> not covered by the bus type or driver. That's why there is only one >>>>> set of PM domain callbacks per device and I don't quite see how and >>>>> why it would be useful to add more of them in there. >>> >>> @Rafael: Re: why it would be useful... >>> >>> Many ARM SoCs have devices that have independent power rails for the >>> memory and the logic of an IP block. For example, while powering off >>> the logic you could keep the memory at a retention voltage, so you'd >>> want to treat those power domains separately. >>> >>> Today, in order to model this, you'd have to create another (dummy) >>> device, just for the memory and put it in its own domain so the two >>> could be controlled separately. >> >> Perhaps if you want to use genpd for that. :-) >> >> Let me rephrase, though. I don't see why and how it would be useful >> to intercept the flow of PM callbacks for a given device more than >> once. > > In this RFC, all I was proposing is that we create a dummy pm-domain > that is a child of the actual pm-domains it uses and this new dummy > pm-domain is associated with the device. Hence, you are still only > intercepting the flow of PM callback once even with this approach. I am > just using the parent-child relationship to ensure that all require > pm-domains are turned on thats all. Sorry if I am still missing your point! No, you aren't, thanks for explaining that! Thanks, Rafael