On Mon, Nov 17, 2014 at 04:44:56PM -0500, Alan Stern wrote:
> On Mon, 17 Nov 2014, Dmitry Torokhov wrote:
>
> > > When the runtime PM core invokes a power domain's callback routine,
> > > what does the domain's routine usually do? Does it go ahead and invoke
> > > the driver's callback? Or does it try to invoke the subsystem's
> > > callback?
> > >
> > > Obviously this depends on how the power domain code is written. But
> > > suppose every power domain would always use the same strategy as the PM
> > > core: Invoke the subsystem's callback if there is one; otherwise invoke
> > > the driver's callback.
> > >
> > > Then there wouldn't be a problem. Even when a runtime-resume went via
> > > the power domain, the subsystem would still be able to protect the
> > > not-yet-bound driver from being called.
> > >
> > > (... Unless the subsystem itself was incapable of doing this the right
> > > way. But subsystems can be fixed.)
> >
> > The genpd code currently starts by powering on the domain (if it is not
> > on already) and then does "device restore" which is:
> >
> > /**
> > * pm_genpd_default_restore_state - Default PM domians "restore device state".
> > * @dev: Device to handle.
> > */
> > static int pm_genpd_default_restore_state(struct device *dev)
> > {
> > int (*cb)(struct device *__dev);
> >
> > cb = dev_gpd_data(dev)->ops.restore_state;
> > if (cb)
> > return cb(dev);
> >
> > if (dev->type && dev->type->pm)
> > cb = dev->type->pm->runtime_resume;
> > else if (dev->class && dev->class->pm)
> > cb = dev->class->pm->runtime_resume;
> > else if (dev->bus && dev->bus->pm)
> > cb = dev->bus->pm->runtime_resume;
> > else
> > cb = NULL;
> >
> > if (!cb && dev->driver && dev->driver->pm)
> > cb = dev->driver->pm->runtime_resume;
> >
> > return cb ? cb(dev) : 0;
> > }
> >
> > So I guess bus (or class or type) can take care of it.
>
> The bus could. I don't think the class or type knows when a driver is
> being probed.
>
> > Except buses
> > usually call pm_generic_runtime_resume() which ends up fetching driver's
> > callbacks. Maybe pm_generic_runtime_*() need be a bit smarter?
>
> No, the bus subsystem needs to be smarter. It shouldn't call
> pm_generic_runtime_resume() if the driver hasn't been probed yet, or if
> the driver has already been unbound from the device.
But that code wold be exactly the same for all buses, right? So why
can't pm_generic_runtime_resume() be smarter?
However, is it allowed to call pm_runtime_get_sync() on devices that
didn't issue pm_runtime_enable()?
Thanks.
--
Dmitry
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