Messages in this thread | | | Date | Fri, 30 Apr 2004 12:07:06 -0700 | From | Todd Poynor <> | Subject | Re: [PATCH] Hotplug for device power state changes |
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Benjamin Herrenschmidt wrote:
>>Now that you mention it, device power hotplug should be synchronous, to >>make sure the power management application has reacted to the changed >>state prior to the device going into actual service (in the case of a >>resume). > > > This is dangerous. > > If the device you are suspending is on the VM path in any way, > beeing synchronous with a userland call can deadlock you solid. > > This is even more true for system suspend where we are suspending > all devices including the main swap/storage.
Well, this feature is intended to allow power management of appropriate devices; using sysfs or a driver call to individually suspend a device required for proper system operation would be a danger, hotplug notification or no. And the individual device notifications provided by the patch under discussion are not for use during a system-wide suspend/resume sequence. I would imagine system suspend/resume would be separate events that probably would not notify of the individual device suspends/resumes performed as a consequence. At any rate, yes, this would occur outside of the code path that freezes processes and such.
-- Todd Poynor MontaVista Software
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