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.
Alan Stern
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