From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755537Ab3KFWCO (ORCPT ); Wed, 6 Nov 2013 17:02:14 -0500 Received: from iolanthe.rowland.org ([192.131.102.54]:46190 "HELO iolanthe.rowland.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1754518Ab3KFWCN (ORCPT ); Wed, 6 Nov 2013 17:02:13 -0500 Date: Wed, 6 Nov 2013 17:02:12 -0500 (EST) From: Alan Stern X-X-Sender: stern@iolanthe.rowland.org To: "Rafael J. Wysocki" cc: Tomi Valkeinen , Greg Kroah-Hartman , Ulf Hansson , Kevin Hilman , Linus Walleij , Archit Taneja , linux-kernel , "linux-pm@vger.kernel.org" Subject: Re: Async runtime put in __device_release_driver() In-Reply-To: <1457511.dE2lGbyvKX@vostro.rjw.lan> Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 6 Nov 2013, Rafael J. Wysocki wrote: > On Wednesday, November 06, 2013 09:51:42 AM Tomi Valkeinen wrote: > > On 2013-11-05 23:29, Ulf Hansson wrote: > > > On 23 October 2013 12:11, Tomi Valkeinen wrote: > > >> Hi, > > >> > > >> I was debugging why clocks were left enabled after removing omapdss > > >> driver, and I found this commit: > > >> > > >> fa180eb448fa263cf18dd930143b515d27d70d7b (PM / Runtime: Idle devices > > >> asynchronously after probe|release) > > >> > > >> I don't understand how that is supposed to work. > > >> > > >> When a driver is removed, instead of using pm_runtime_put_sync() the > > >> commit uses pm_runtime_put(), so the runtime_suspend call is queued. But > > >> who is going to handle the queued suspend call, as the driver is already > > >> removed? At least in my case, obviously nobody, as I only get > > >> runtime_resume call in my driver, never the runtime_suspend. > > >> > > >> Is there something I need to add to my driver to make this work, or > > >> should that part of the patch be reverted? > > > > > > I believe it is quite common that a device driver calls > > > pm_runtime_get_sync as a part of it's remove callback, then it > > > explicitly returns it's resources that has been fetched during probe. > > > Like a clk_disable_unprepare for example. > > > > I guess you mean the driver calls pm_runtime_get_sync _and_ > > pm_runtime_put_sync as part of its remove callback? > > > > Probably bus drivers need to do that, but for memory mapped devices in a > > SoC, I don't think there's normally any need to do > > pm_runtime_get/put_sync during the remove callback. > > > > > The idea behind the change in __device_release_driver, was to try to > > > prevent devices from going active->idle->active and instead just > > > remain active (if possible). > > > > > > In your case, which seems like a more modern way of implementing > > > "remove", you shall call "pm_runtime_suspend" to make sure the > > > runtime_suspend callbacks gets called. > > > > And as far as I understand, the change creates an explicit requirement > > to do either pm_runtime_get/put_sync or pm_runtime_suspend inside > > driver's remove callback. If so, that should be mentioned in big red > > letters in the pm-runtime documentation. > > > > The runtime_pm.txt doc does mention something related to this (and btw, > > the doc says pm_runtime_put_sync is being called, which is no longer > > true), but nothing clear about how the driver remove callback must be > > implemented. > > That's correct. > > > I tried grepping the kernel sources to find out if pm_runtime_suspend is > > widely used to get SoC platform devices to suspend, but it doesn't seem > > like it is. I didn't see pm_runtime_get/put_sync being used in remove > > callbacks widely either, but that was more difficult one to grep. > > I think your observations are valid, which unfortunately means that we'll > need to revert the commit in question, because it has changed the behavior > that drivers are perfectly fine to expect given the existing documentation > etc. It looks like the change was premature at least. > > Greg, I wonder if you can queue up a revert of fa180eb448fa for 3.13, or > do you want me to do that? Would it be better to leave the runtime-idle callbacks (invoked during probe) async and revert only the change to __device_release_driver()? Having an async callback after probe shouldn't cause problems, because the driver will then be bound (assuming the probe succeeded). Alan Stern