Re: [PATCH/RFC] MMC: remove unbalanced pm_runtime_suspend()

Alan Stern
2011-04-21T18:36:09Z

On Thu, 21 Apr 2011, Rafael J. Wysocki wrote:

> > > What about making a rule that it is invalid to schedule a future suspend
> > > or queue a resume request of a device whose driver is being removed?
> > >
> > > Arguably, we can't prevent people from shooting themselves in the foot this
> > > way or another and I'm not sure if this particular case is worth additional
> > > handling.
> >
> > After thinking about this, I tend to agree. The synchronization
> > issues, combined with the unknown needs of the driver, make this very
> > difficult to handle in the PM core.
> >
> > Here's another possible approach: If a driver wants to leave its device
> > in a powered-down state after unbinding then it can invoke its own
> > runtime_suspend callback directly, in the following way:
> >
> > ... unregister all child devices below dev ...
> > pm_runtime_disable(dev);
> > if (dev->power.runtime_status != RPM_SUSPENDED) {
> > pm_set_suspended(dev);
> > my_runtime_suspend_callback(dev);
> > }
>
> I think this would work too, but then possibly many drivers would have to
> do the same thing in their "remove" routines.
>
> > There may be issues regarding coordination with the subsystem or the
> > power domain; at the moment it's not clear what should be done. Maybe
> > the runtime-PM core should include an API for directly invoking the
> > appropriate callbacks.
>
> If we choose this approach, then yes, we should provide a suitable API, but
> I'm still thinking it would be simpler to move the pm_runtime_put_sync() before driver_sysfs_remove() and make the rule as I said previously. :-)

The problem is synchronization. At what point is the driver supposed
to stop queuing runtime PM requests? It would have to be sometime
before the pm_runtime_barrier() call. How is the driver supposed to
know when that point is reached? The remove routine isn't called until
later.

Alan Stern