Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753354AbaFRPax (ORCPT ); Wed, 18 Jun 2014 11:30:53 -0400 Received: from iolanthe.rowland.org ([192.131.102.54]:46579 "HELO iolanthe.rowland.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1752169AbaFRPaw (ORCPT ); Wed, 18 Jun 2014 11:30:52 -0400 Date: Wed, 18 Jun 2014 11:30:51 -0400 (EDT) From: Alan Stern X-X-Sender: stern@iolanthe.rowland.org To: "Rafael J. Wysocki" cc: Allen Yu , Pavel Machek , Len Brown , Greg Kroah-Hartman , , Subject: Re: [PATCH 1/1] PM / Runtime: let rpm_resume fail if rpm disabled and device suspended. In-Reply-To: <2420304.GaXVpqVQD5@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 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. > > 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. Allen, what do you think? Alan Stern -- 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/