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Message-Id: <201106182301.04090.rjw@sisk.pl>
Date: Sat, 18 Jun 2011 23:01:03 +0200
From: "Rafael J. Wysocki" <rjw@...k.pl>
To: Alan Stern <stern@...land.harvard.edu>
Cc: linux-pm@...ts.linux-foundation.org, linux-omap@...r.kernel.org,
Kevin Hilman <khilman@...com>, Paul Walmsley <paul@...an.com>,
Magnus Damm <magnus.damm@...il.com>,
LKML <linux-kernel@...r.kernel.org>
Subject: Re: [linux-pm] calling runtime PM from system PM methods
On Saturday, June 18, 2011, Alan Stern wrote:
> On Sat, 18 Jun 2011, Rafael J. Wysocki wrote:
>
> > On Friday, June 17, 2011, Rafael J. Wysocki wrote:
> > > On Friday, June 17, 2011, Alan Stern wrote:
> > > > On Fri, 17 Jun 2011, Rafael J. Wysocki wrote:
> > > >
> > > > > Having considered that a bit more I see that, in fact, commit
> > > > > e8665002477f0278f84f898145b1f141ba26ee26 (PM: Allow pm_runtime_suspend() to
> > > > > succeed during system suspend) has introduced at least one regression.
> > > > > Namely, the PCI bus type runs pm_runtime_resume() in its .prepare()
> > > > > callback to guarantee that devices will be in a well known state before
> > > > > the PCI .suspend() and .suspend_noirq() callbacks are executed.
> > > > > Unfortunately, after commit e8665002477f0278f84f898145b1f141ba26ee26 this
> > > > > isn't valid any more, because devices can be runtime-suspend after the
> > > > > pm_runtime_resume() in .prepare() has run.
> > > > >
> > > > > USB seems to do something similar in choose_wakeup().
> > > > >
> > > > > So, either the both of these subsystems should be modified to use
> > > > > pm_runtime_get_sync() and then pm_runtime_put_<something>() some time
> > > > > during resume, or we should revert commit e8665002477f0278f84f898145b1f141ba26ee26.
> > > >
> > > > pm_runtime_put_noidle would be appropriate.
> > > >
> > > > > Quite frankly, which shouldn't be a surprise to anyone at this point, I'd
> > > > > prefer to revert that commit for 3.0.
> > > >
> > > > Maybe we can compromise. Instead of reverting that commit outright,
> > > > put the get_noresume just before the suspend callback and put the
> > > > put_sync just after the resume callback.
> > >
> > > That wouldn't fix the PCI problem, though, because it would leave a small
> > > window in which the device could be suspended after the pm_runtime_resume()
> > > in pci_pm_prepare() had run.
> >
> > That said, the PCI case can be solved with a separate patch and if the other
> > subsystems are not affected, perhaps that's the best approach.
>
> Yes, it would be a simple change.
>
> > Still, I'd like to make sure that there won't be any races between runtime
> > PM and .suspend_noirq() and .resume_noirq() callbacks, so I'd like to apply
> > the patch below.
> >
> > Thanks,
> > Rafael
> >
> > ---
> > drivers/base/power/main.c | 7 ++++++-
> > 1 file changed, 6 insertions(+), 1 deletion(-)
> >
> > Index: linux-2.6/drivers/base/power/main.c
> > ===================================================================
> > --- linux-2.6.orig/drivers/base/power/main.c
> > +++ linux-2.6/drivers/base/power/main.c
> > @@ -591,6 +591,8 @@ void dpm_resume(pm_message_t state)
> > async_error = 0;
> >
> > list_for_each_entry(dev, &dpm_suspended_list, power.entry) {
> > + pm_runtime_get_noresume(dev);
> > + pm_runtime_enable(dev);
> > INIT_COMPLETION(dev->power.completion);
> > if (is_async(dev)) {
> > get_device(dev);
> > @@ -614,6 +616,7 @@ void dpm_resume(pm_message_t state)
> > }
> > if (!list_empty(&dev->power.entry))
> > list_move_tail(&dev->power.entry, &dpm_prepared_list);
> > + pm_runtime_put_noidle(dev);
> > put_device(dev);
> > }
> > mutex_unlock(&dpm_list_mtx);
> > @@ -939,8 +942,10 @@ int dpm_suspend(pm_message_t state)
> > put_device(dev);
> > break;
> > }
> > - if (!list_empty(&dev->power.entry))
> > + if (!list_empty(&dev->power.entry)) {
> > list_move(&dev->power.entry, &dpm_suspended_list);
> > + pm_runtime_disable(dev);
> > + }
>
> The put_noidle is in the wrong place for async resumes. Likewise for
> the pm_runtime_disable() and async suspends. Also this runs into
> problems if a device is never suspended (i.e., if the sleep transition
> aborts before suspending that device).
I overlooked that, thanks for pointing it out.
Well, assuming that https://patchwork.kernel.org/patch/893722/ is applied,
which is going to be, I think we can put
+ pm_runtime_get_noresume(dev);
+ pm_runtime_enable(dev);
in device_resume() after the dev->power.is_suspended check and
pm_runtime_put_noidle() under the End label. That cause them to
be called under the device lock, but that shouldn't be a big deal.
Accordingly, we can call pm_runtime_disable(dev) in __device_suspend(),
right next to the setting of power.is_suspended.
This is implemented by the patch below.
Thanks,
Rafael
---
drivers/base/power/main.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)
Index: linux-2.6/drivers/base/power/main.c
===================================================================
--- linux-2.6.orig/drivers/base/power/main.c
+++ linux-2.6/drivers/base/power/main.c
@@ -521,6 +521,9 @@ static int device_resume(struct device *
if (!dev->power.is_suspended)
goto Unlock;
+ pm_runtime_get_noresume(dev);
+ pm_runtime_enable(dev);
+
if (dev->pwr_domain) {
pm_dev_dbg(dev, state, "power domain ");
error = pm_op(dev, &dev->pwr_domain->ops, state);
@@ -557,6 +560,7 @@ static int device_resume(struct device *
End:
dev->power.is_suspended = false;
+ pm_runtime_put_noidle(dev);
Unlock:
device_unlock(dev);
@@ -888,7 +892,10 @@ static int __device_suspend(struct devic
}
End:
- dev->power.is_suspended = !error;
+ if (!error) {
+ dev->power.is_suspended = true;
+ pm_runtime_disable(dev);
+ }
Unlock:
device_unlock(dev);
--
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