On Friday, June 20, 2014 02:34:14 PM Kevin Hilman wrote: > Alan Stern <st...@rowland.harvard.edu> writes: > > > On Fri, 20 Jun 2014, Rafael J. Wysocki wrote: > > > >> > For a general device, the fact that dev->power.is_suspended is set > >> > means the device _has_ been powered down. Even though the > >> > runtime_status may not have changed, the PM core has to assume the > >> > device is not available for use. > >> > >> This seems to go a bit too far. What power.is_suspended actually means is > >> that __device_suspend() has run for the device successfully. What the > >> implications of that are depends on the bus type (or subsystem in general) > >> and device driver. > >> > >> > While your I2C devices may be useable even after the ->suspend callback > >> > returns, for most devices this isn't true. So we shouldn't allow > >> > rpm_resume() to return imediately when is_suspended is set. > >> > >> I can agree with that. > > > > We really do need to decide more precisely how runtime PM and system PM > > will interact. > > Yes! > > > Should ->runtime_resume callbacks be allowed after ->suspend has > > returned? > > Abolutely. > > > Kevin has stated that some devices do need this ability. But most > > don't. > > Does it matter if most don't? As long a some do, we need to support > this. It may not be "most" devices, but on the (mostly embedded) SoCs I > work on, the devices that do need this tend to be rather crucial core > devices that are used during the PM of other devices (e.g. I2C, SPI, > GPIOs, etc. etc.) > > > The PM core needs to handle these conflicting requirements > > somehow. > > I agree. We've gone back and forth a few times on the various > interactions between system PM and runtime PM over the years but it > seems there are still things to clarify.
Well, we only considered a specific use case every time without looking at the big picture, mostly because we didn't really know what the big picture was. I guess today we have enough experience to try to address all of these problems together. I guess we need to start with making a list of different types of bus type/driver behavior existing today and how the core is supposed to interact with them. Rafael -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
