On Tue, 18 Nov 2014, Dmitry Torokhov wrote: > OK. Another question then: pm_runtime_get_noresume() does literally this: > > atomic_inc(&dev->power.usage_count); > > So who is responsible for actually waking up parent device and/or power > domain? Is it simply missing because we did not really have PM domains > before? Ths bus is responsible for making sure that all the standard resources are available -- that is, all the resources that would be needed by a normal device on that bus. Anything beyond that (such as special-purpose clocks) has to be set up by the driver. Thus the bus would insure that the device was powered, its parent was resumed, and the usual clock inputs were enabled. And of course, one mechanism for doing this is to runtime-resume the power domain. Often the bus doesn't have to do anything special to resume the device's parent. This is because the device gets probed when it is registered, which happens when it is discovered, and the discovery is done by the parent's driver as part of its normal activity. Since the parent has to be powered up to carry out this normal activity, nothing more is needed. (Of course, devices can get probed at other times too, not just when they are discovered. For example, a device might get probed when a driver module is loaded, and that can occur at any time. So in general it might indeed be necessary for the bus to wake up the parent before calling the driver's probe routine.) Alan Stern -- 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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