On Tuesday, November 04, 2014 01:05:21 AM Dmitry Torokhov wrote: > On Tue, Nov 04, 2014 at 09:54:19AM +0100, Ulf Hansson wrote: > > [...] > > > > > Generally, there are two or even three levels of runtime PM handling, > > > driver, (possibly) bus type and (possibly) PM domain (and multiple levels > > > of these are possible in principle). All of them have to be initialized > > > at different times. > > > > > > Quite arguably, the PM domain and/or bus type runtime PM handling should > > > be initialized even before registerind the device or during device > > > registration. Doing that later may be too late. When the device has been > > > registered, runtime PM should work to an extent allowing the driver to access > > > the device and configure it further after calling pm_runtime_resume(). > > > > > > Of course, if ->probe() is to call pm_runtime_resume() for this purpose, > > > it must take the fact that the driver's own ->runtime_resume() may be called > > > as a result of this into account. That's why I'm asking whether or not the > > > core should call pm_runtime_resume() before calling really_probe() in a > > > followup branch of this thread. > > > > I am reading the other thread, let's see. > > > > > > > > The driver's own runtime PM handling must be initialized in the driver and > > > the only place suitable for that is ->probe(). However, it needs to be done > > > *before* the driver's own ->runtime_resume() or ->runtime_suspend() callback > > > is executed. If that is done properly, it should be possible to cover > > > both the CONFIG_PM_RUNTIME set/unset cases in that code. > > > > > > And I wouldn't recommend anyone to do the runtime PM initialization in > > > ->runtime_resume() (when it is called for the first time), as that would be > > > error prone and fragile. > > > > Great! That's means we are at least aligned on this topic. :-) > > > > > > > >> The AMBA bus and some of its drivers a good example of how this has > > >> been implemented: > > >> driver/amba/bus.c > > >> drivers/mmc/host/mmci.c > > >> drivers/spi/spi-pl022.c > > >> > > >> This conclusion I have made from this is: > > >> - Using pm_runtime_get_sync() during the ->probe() path to explicitly > > >> power up a PM domain, is not suitable as the _common_ solution to > > >> solve the race condition. It certainly may work for some scenarios, > > >> but not for those I am looking at. > > > > > > I think, however, that it might work if the core calls pm_runtime_get_sync() > > > from driver_probe_device(). > > > > Currently this won't work. > > > > That's because the buses' ->probe() are invoked in this path and they > > are doing the attachment of the device to its PM domain. > > > > In other words, we can't power up the PM domain using > > pm_runtime_get_sync(), until the device has been attached to its PM > > domain. Right? > > > I think this is one of the issues that we have there. Why do we conflate > probing and placing the device into a power domain? The latter should > happen when we register the device. The fact that a device was probed > and has a driver bound or not bound to it should have no bearing on > whether the device is member of power domain or not. Agreed. Rafael -- To unsubscribe from this list: send the line "unsubscribe linux-samsung-soc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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