From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751485Ab3KFWsg (ORCPT ); Wed, 6 Nov 2013 17:48:36 -0500 Received: from mail-la0-f42.google.com ([209.85.215.42]:53147 "EHLO mail-la0-f42.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750717Ab3KFWse (ORCPT ); Wed, 6 Nov 2013 17:48:34 -0500 User-Agent: K-9 Mail for Android In-Reply-To: <1910973.CpzEs44S3m@vostro.rjw.lan> References: <1910973.CpzEs44S3m@vostro.rjw.lan> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Subject: Re: Async runtime put in __device_release_driver() From: Ulf Hansson Date: Wed, 06 Nov 2013 23:48:24 +0100 To: "Rafael J. Wysocki" , Alan Stern CC: Tomi Valkeinen , Greg Kroah-Hartman , Kevin Hilman , Linus Walleij , Archit Taneja , linux-kernel , "linux-pm@vger.kernel.org" Message-ID: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org "Rafael J. Wysocki" skrev: >On Wednesday, November 06, 2013 05:02:12 PM Alan Stern wrote: >> 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). > >Right. OK, I'll prepare a patch. That seems like a good way forward. Also I appoligize for not updating the doc as part of the original patch. Kind regards Ulf Hansson > >Thanks, >Rafael