Re: use of pm_runtime_disable() from driver probe?

Rafael J. Wysocki
2012-07-10T19:41:24Z

On Tuesday, July 10, 2012, Rafael J. Wysocki wrote:
> On Tuesday, July 10, 2012, Alan Stern wrote:
> > On Tue, 10 Jul 2012, Rafael J. Wysocki wrote:
> >
> > > > > Anyway, you can't force the device into a low-power state using
> > > > > runtime PM after a failing probe, at least in general.
> > > >
> > > > Well, using PM domains, that's exactly what can happen if the driver
> > > > doesn't call pm_runtime_disable() because the _put_sync() in the driver
> > > > core will trigger the PM domain callbacks.
> > >
> > > OK, so if you have PM domains, then the case is equivalent to having a bus
> > > type with its own runtime PM callbacks. In that case, if .probe() fails,
> > > it obviously doesn't mean that the device shouldn't be power managed,
> > > so the driver shouldn't call pm_runtime_disable().
> > >
> > > Generally, if runtime PM was enabled for a device before .probe() has been
> > > called, the driver shouldn't disable it in .probe() whatever the reason,
> > > because it may not have enough information for deciding whether or not
> > > runtime PM should be disabled.
> >
> > So if the PM domain code called pm_runtime_enable() then the domain
> > code should be responsible for calling pm_runtime_disable() too,
> > presumably after putting the device back into a low-power state. I'm
> > not sure when that would occur, however. Immediately after registering
> > the device, if no driver is bound?
> >
> > In the case where the probe routine called pm_runtime_enable(), you're
> > stuck. The probe routine _has_ to call pm_runtime_disable() when a
> > failure occurs, to keep the disable count balanced.
>
> Yes, I has just been thinking about that.
>
> If .probe() enabled runtime PM and called pm_runtime_get_sync() (or _resume),
> it can't clean up properly in case of an error, because its
> pm_runtime_put_sync() (or _suspend) won't be effective and you're right that
> it has to call pm_runtime_disable().
>
> So, we don't handle this particular case correctly.
>
> I'm not sure what the solution should be, though. We could remove the
> runtime PM operations around really_probe(), but then there may be drivers
> assuming that the core will call pm_runtime_put_sync() after .probe()
> has returned.

I have an idea.

What about the following patch? It shouldn't matter except for the cases when
.probe() attempts to suspend the device by itself.

---
drivers/base/dd.c | 7 ++-----
1 file changed, 2 insertions(+), 5 deletions(-)

Index: linux/drivers/base/dd.c
===================================================================
--- linux.orig/drivers/base/dd.c
+++ linux/drivers/base/dd.c
@@ -356,10 +356,8 @@ int driver_probe_device(struct device_dr
pr_debug("bus: '%s': %s: matched device %s with driver %s\n",
drv->bus->name, __func__, dev_name(dev), drv->name);

- pm_runtime_get_noresume(dev);
- pm_runtime_barrier(dev);
ret = really_probe(dev, drv);
- pm_runtime_put_sync(dev);
+ pm_runtime_idle(dev);

return ret;
}
@@ -406,9 +404,8 @@ int device_attach(struct device *dev)
ret = 0;
}
} else {
- pm_runtime_get_noresume(dev);
ret = bus_for_each_drv(dev->bus, NULL, dev, __device_attach);
- pm_runtime_put_sync(dev);
+ pm_runtime_idle(dev);
}
out_unlock:
device_unlock(dev);