[PATCH v3 0/9] PM / Domains: Fix race conditions during boot

[Rafael J. Wysocki]

On Tuesday, November 04, 2014 10:29:20 AM Dmitry Torokhov wrote:
> On Tue, Nov 04, 2014 at 06:01:44PM +0100, Ulf Hansson wrote:
> > >>
> > >> Devices that are created while "discoverable buses" are being probed
> > >> can't be attached to a PM domain before the probing is done, because
> > >> those simply doesn't exist.
> > >
> > > Honestly, I'm not sure what you're talking about.
> > >
> > > Devices on a "discoverable* bus (say PCI) are added when the *controller* is
> > > probed, not when *they* are probed.
> > 
> > Okay, so maybe "discoverable buses" isn't the proper term.
> > 
> > >
> > > You very much need to have a struct device registered to be able to call
> > > really_probe() for it.
> > 
> > Yes. But my point is that the struct device may be created dynamically
> > at some point in time.
> 
> And that is fine.
> 
> > 
> > This is how mmc/sd/sdio cards are handled. We don't have the
> > information about the card and thus not the struct device of it, until
> > we have detected it. Maybe we could at that point try to add the
> > device to its PM domain?
> 
> Well, I think we need to first define what PM domain they will fall
> into. Do they have to be in one? The concept of power domain, as far as I
> understand it, is needed when we need to form relations going outside
> the standard parent/child relationship. Here we have a controller and
> then one or more cards in it. To be able to use card you need to power
> up parent and you can not power down parent until all children are
> powered down.
> 
> But in any case, device discovery and binding them to drivers are 2
> separate steps. You have a PCI bus. You enumerate it - new PCI devices
> are created. Some of them may be put in a certain power domain. You then
> bind drivers to PCI devices (not strictly 'then' but we could implement
> driver core to postpone binding until current round of enumeration is
> complete) - and you discover USB controller and maybe i2c controller.
> Then you bind drivers to them which causes enumeration of the new bus
> and new devices are created. But in all these cases enumeration and
> creation of new 'struct device's, and driver binding are logically
> separate steps.
> 
> > 
> > >
> > >> Now, I haven't yet seen a demand for such a cases, but it seems wrong
> > >> to not consider them. The current solution cover these.
> > >
> > > Oh dear.  Please rethink this.
> > 
> > Currently, dev_pm_domain_attach() is being invoked at the point when a
> > SDIO card has been found. From sdio_add_func(). How would that be
> > solved?
> > 
> 
> It is probably the one place where we currently doing it correctly (form
> logical point of view, not implementation wise - implementation wise in
> sdio we add device to power domain after calling device_add() which
> means that probe() could have been called before we added the new device
> to any power domain).

I agree.  Ideally, devices should be added to power (or generally PM) domains
before registration.  That is, before calling device_add() for them.

That's the first thing to fix here.

Rafael