Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755647AbaFRXjn (ORCPT ); Wed, 18 Jun 2014 19:39:43 -0400 Received: from v094114.home.net.pl ([79.96.170.134]:65382 "HELO v094114.home.net.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1753354AbaFRXjl (ORCPT ); Wed, 18 Jun 2014 19:39:41 -0400 From: "Rafael J. Wysocki" To: Alan Stern Cc: Allen Yu , Pavel Machek , Len Brown , Greg Kroah-Hartman , linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/1] PM / Runtime: let rpm_resume fail if rpm disabled and device suspended. Date: Thu, 19 Jun 2014 01:57:16 +0200 Message-ID: <3528855.Z370J7O75B@vostro.rjw.lan> User-Agent: KMail/4.11.5 (Linux/3.15.0-rc5+; KDE/4.11.5; x86_64; ; ) In-Reply-To: References: MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit 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 Wednesday, June 18, 2014 11:30:51 AM Alan Stern wrote: > On Tue, 17 Jun 2014, Rafael J. Wysocki wrote: > > > On Tuesday, June 17, 2014 10:37:03 PM Rafael J. Wysocki wrote: > > > On Tuesday, June 17, 2014 10:26:14 PM Rafael J. Wysocki wrote: > > > > On Tuesday, June 17, 2014 10:11:32 AM Alan Stern wrote: > > > > > On Mon, 16 Jun 2014, Rafael J. Wysocki wrote: > > > > > > > > > > > > For reasons having nothing to do with Allen's suggested change, I > > > > > > > wonder if we shouldn't replace this line with something like: > > > > > > > > > > > > > > - else if (dev->power.disable_depth == 1 && dev->power.is_suspended > > > > > > > + else if (dev->power.disable > 0 && !dev->power.is_suspended > > > > > > > && dev->power.runtime_status == RPM_ACTIVE) > > > > > > > retval = 1; > > > > > > > > > > > > > > It seems that I've been bitten by this several times in the past. > > > > > > > When a device is disabled for runtime PM, and more or less permanently > > > > > > > stuck in the RPM_ACTIVE state, calls to pm_runtime_resume() or > > > > > > > pm_runtime_get_sync() shouldn't fail. > > > > > > > > > > > > > > For example, suppose some devices of a certain type support runtime > > > > > > > power management but others don't. We naturally want to call > > > > > > > pm_runtime_disable() for the ones that don't. But we also want the > > > > > > > same driver to work for all the devices, which means that > > > > > > > pm_runtime_get_sync() should return success -- otherwise the driver > > > > > > > will think that something has gone wrong. > > > > > > > > > > > > > > Rafael, what do you think? > > > > > > > > > > > > That condition is there specifically to take care of the system suspend > > > > > > code path. It means that if runtime PM is disabled, but it only has been > > > > > > disabled by the system suspend code path, we should treat the device as > > > > > > "active" (ie. return 1). That won't work after the proposed change. > > > > > > > > > > Ah, yes, quite true. Okay, suppose we replace that line with just: > > > > > > > > > > + else if (dev->power.disable > 0 > > > > > > > > > > > I guess drivers that want to work with devices where runtime PM may be > > > > > > disabled can just check the return value of rpm_resume() for -EACCES? > > > > > > > > > > They could, but it's extra work and it's extremely easy to forget > > > > > about. I'd prefer not to do things that way. > > > > > > > > In that case we need to audit all code that checks the return value of > > > > __pm_runtime_resume() to verify that it doesn't depend on the current > > > > behavior in any way. It shouldn't, but still. > > > > > > > > Also we probably should drop the -EACCES return value from rpm_resume() in the > > > > same patch, because it specifically only covers the dev->power.disable > 0 case > > > > (which BTW is consistent with the suspend side of things, so I'm totally unsure > > > > about that being the right thing to do to be honest). > > It's still the correct action with runtime PM is disabled and the > device's runtime_status isn't RPM_ACTIVE. Well, we used to have the notion that runtime_status is not meaningful for devices with dev->power.disable_depth greater than 0 (except for the special case in the suspend code path where we know why it is greater than 0). I think it was useful. :-) > > > Perhaps it'd be better to rework __pm_runtime_resume() to convert the -EACCES > > > return value from rpm_resume() into 0 if RPM_GET_PUT is set? > > > > Or do something like this? > > > > --- > > drivers/base/power/runtime.c | 3 ++- > > 1 file changed, 2 insertions(+), 1 deletion(-) > > > > Index: linux-pm/drivers/base/power/runtime.c > > =================================================================== > > --- linux-pm.orig/drivers/base/power/runtime.c > > +++ linux-pm/drivers/base/power/runtime.c > > @@ -608,7 +608,8 @@ static int rpm_resume(struct device *dev > > repeat: > > if (dev->power.runtime_error) > > retval = -EINVAL; > > - else if (dev->power.disable_depth == 1 && dev->power.is_suspended > > + else if (((dev->power.disable_depth > 0 && (rpmflags & RPM_GET_PUT)) > > + || (dev->power.disable_depth == 1 && dev->power.is_suspended)) > > && dev->power.runtime_status == RPM_ACTIVE) > > retval = 1; > > else if (dev->power.disable_depth > 0) > > So pm_runtime_resume() and pm_request_resume() would still fail, but > pm_runtime_get() and pm_runtime_get_sync() would work? I'm not sure > about the reason for this distinction. The meaning of pm_runtime_get()/pm_runtime_get_sync() is "prevent the device from being suspended from now on and resume it if necessary" while "runtime PM disabled and runtime_status == RPM_ACTIVE" may be interpreted as "not necessary to resume", so it is reasonable to special case this particular situation for these particular routines IMHO. Rafael -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/