From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934776AbcKVWeJ (ORCPT ); Tue, 22 Nov 2016 17:34:09 -0500 Received: from mail-wj0-f193.google.com ([209.85.210.193]:34001 "EHLO mail-wj0-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933325AbcKVWeH (ORCPT ); Tue, 22 Nov 2016 17:34:07 -0500 X-Greylist: delayed 2300 seconds by postgrey-1.27 at vger.kernel.org; Tue, 22 Nov 2016 17:34:06 EST MIME-Version: 1.0 In-Reply-To: References: <1474367287-10402-1-git-send-email-jonathanh@nvidia.com> <90faea7d-65b6-590a-83f1-24fcdffa0569@nvidia.com> <63670abf-1d58-a7e3-6927-0c815d44d8a1@nvidia.com> From: "Rafael J. Wysocki" Date: Tue, 22 Nov 2016 22:55:33 +0100 X-Google-Sender-Auth: ORY700AK7KYEPEeLo5iWu7Ki6Z0 Message-ID: Subject: Re: [RFC PATCH 0/3] PM / Domains: Add support for devices that require multiple domains To: Kevin Hilman Cc: Jon Hunter , "Rafael J. Wysocki" , 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 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. Thanks, Rafael