On 4 November 2014 10:05, Dmitry Torokhov <dmitry.torokhov@xxxxxxxxx> 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. 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. 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. Kind regards Uffe -- 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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