From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756876Ab1AaXCU (ORCPT ); Mon, 31 Jan 2011 18:02:20 -0500 Received: from ogre.sisk.pl ([217.79.144.158]:55400 "EHLO ogre.sisk.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754296Ab1AaXCR (ORCPT ); Mon, 31 Jan 2011 18:02:17 -0500 From: "Rafael J. Wysocki" To: Kevin Hilman , Magnus Damm Subject: Re: [RFC][PATCH] Power domains for platform bus type Date: Tue, 1 Feb 2011 00:01:51 +0100 User-Agent: KMail/1.13.5 (Linux/2.6.38-rc2+; KDE/4.4.4; x86_64; ; ) Cc: Grant Likely , Alan Stern , "Linux-pm mailing list" , Greg KH , LKML , Len Brown References: <20110131222609.GC27856@angua.secretlab.ca> <87vd1466d8.fsf@ti.com> In-Reply-To: <87vd1466d8.fsf@ti.com> MIME-Version: 1.0 Content-Type: Text/Plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Message-Id: <201102010001.51418.rjw@sisk.pl> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Monday, January 31, 2011, Kevin Hilman wrote: > Grant Likely writes: > > > On Mon, Jan 31, 2011 at 11:16:51PM +0100, Rafael J. Wysocki wrote: > >> On Monday, January 31, 2011, Alan Stern wrote: > >> > On Mon, 31 Jan 2011, Rafael J. Wysocki wrote: > >> > > >> > > On Monday, January 31, 2011, Alan Stern wrote: > >> > > > On Sun, 30 Jan 2011, Rafael J. Wysocki wrote: > >> > > > > >> > > > > > One thing about this implementation is slightly questionable. The new > >> > > > > > power_domain callbacks were added to the __weak platform PM routines, > >> > > > > > which means they will have to be included in every overriding routine > >> > > > > > provided by a platform imiplementation. > >> > > > > > > >> > > > > > Would it be better to separate these things? Have the power_domain > >> > > > > > callbacks occur in a static outer function which then calls a public > >> > > > > > __weak inner function that can be overridden? > >> > > > > > >> > > > > That certainly is a good idea, but I wasn't sure how to do that. It looks > >> > > > > like I could keep the __weak functions as they are and modify > >> > > > > platform_dev_pm_ops instead to point to a new set of function that in turn > >> > > > > would call the __weak ones. For example, the .suspend pointer in > >> > > > > platform_dev_pm_ops might point to a new function, say > >> > > > > platform_pm_full_suspend() that would call the power domain functions and > >> > > > > the "original" platform_pm_suspend(). Is that what you mean? > >> > > > > >> > > > Yes. But what about the platform_bus_set_pm_ops() interface? Should > >> > > > platform-specific replacements for the pm_ops functions also include > >> > > > the power_domain callbacks? > >> > > > >> > > Well, whoever uses platform_bus_set_pm_ops(), he can simply prevent power > >> > > domains from being used by not defining them in the first place. :-) > >> > > >> > But what about the case where the user _does_ want to have power > >> > domains? > >> > >> Ah, OK. The caller of platform_bus_set_pm_ops() will replace the original > >> platform_dev_pm_ops with his own set of operations, so he will not see the > >> power domains. > >> > >> > Do you want to make the replacement routines responsible for > >> > invoking the power-domain callbacks, or should the platform core handle > >> > this automatically? > >> > >> Well, if someone replaces the entire platform_dev_pm_ops object, this means > >> that on his platform power management is substantially different from the > >> generic one. In that case, IMO, he should be responsible for handling all > >> of the subsystem-level aspects of power management, including power domains. > > > > Part of point of doing something like power_domain is to *get rid* of > > platform_bus_set_pm_ops(). It is a horrid, stop-gap interface that > > doesn't scale. I don't think much consideration needs to be made for > > users of platform_bus_set_pm_ops() in this regard. > > As the author of platform_bus_set_pm_ops(), I humbly agree. > > Also, the __weak functions here were obsoleted by > platform_bus_set_pm_ops(). Once Magnus moves to > platform_bus_set_pm_ops() (or this new interface) the __weak attributes > should be removed (c.f. commit log below[1] where > platform_bus_set_pm_ops() was added.) > > Kevin > > commit c64a0926710153b9d44c979d2942f4a8648fd74e > Author: Kevin Hilman > Date: Wed Aug 25 12:50:00 2010 -0700 > > driver core: platform_bus: allow runtime override of dev_pm_ops > > Currently, the platform_bus allows customization of several of the > busses dev_pm_ops methods by using weak symbols so that platform code > can override them. The weak-symbol approach is not scalable when > wanting to support multiple platforms in a single kernel binary. > > Instead, provide __init methods for platform code to customize the > dev_pm_ops methods at runtime. > > NOTE: after these dynamic methods are merged, the weak symbols should > be removed from drivers/base/platform.c. AFAIK, this will only > affect SH and sh-mobile which should be converted to use this > runtime approach instead of the weak symbols. After SH & > sh-mobile are converted, the weak symobols could be removed. > -- So, it seems there are two possibilities, either (1) keep the $subject patch as is in the hope that Magnus will use power domains instead of overriding the __weak callbacks and remove the _weak attribute when that happens, or (2) modify it along the lines suggested by Alan (ie. so that the _weak callbacks stay as they are, but they won't be pointed to by platform_dev_pm_ops directly). I'm pretty much fine with each of them, so I'd prefer to do whichever is generally more useful. Magnus? Rafael