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

Alan Stern
2011-04-21T21:48:31Z

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

> > > 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.
>
> Executing the driver's callback is not an ideal solution either, because
> it simply may be insufficient (it may be necessary to execute the power
> domain and/or subsystem callbacks, pretty much what rpm_suspend() does,
> but without taking the usage counter into consideration).

That's why I suggested a new API. It could do the right callbacks.

> Moreover, if we want the driver's ->remove() to do the cleanup anyway,
> there's not much point in doing any cleanup before in the core. Also,
> there's a little problem that the bus ->remove() is called before the
> driver's ->remove(), so it may not be entirely possible to power down
> the device when the driver's ->remove() is called already.

Actually, the bus->remove() callback (if there is one) is responsible
for invoking the driver's callback. The subsystem should be smart
enough to handle runtime PM requests while the driver's remove callback
is running.

> I think the current code is better than any of the alternatives considered
> so far.

Then you think Guennadi should leave his patch as it is, including the
"reversed" put/get?

Alan Stern