Messages in this thread | | | Date | Wed, 16 Sep 2015 15:27:55 -0400 (EDT) | From | Alan Stern <> | Subject | Re: [PATCH] driver core: Ensure proper suspend/resume ordering |
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On Wed, 16 Sep 2015, Grygorii Strashko wrote:
> I think, It should prohibited to probe devices during suspend/hibernation. > And solution introduced in this patch might help to fix it - > in general, we could do : > - add sync point on suspend enter: wait_for_device_probe() and > - prohibit probing: move all devices which will request probing into > deferred_probe list > - one suspend exit: allow probing and do driver_deferred_probe_trigger
That could work; it's a good idea.
> I'd like to mention here that this patch will work only > if dmp_list will be filled according device creation order ("parent<-child" dependencies) > *AND* according device's probing order ("supplier<-consumer"). > So, if there is the case when Parent device can be probed AFTER its children > - it will not work, because "parent<-child" dependencies will not be tracked > any more :( Sry, I could not even imagine that such crazy case exist :'(
If we avoid moving devices to the end of the dpm_list when they already have children, then we should be okay, right?
> Are there any other subsystems with the same behavior like PCI?
I don't know.
> If not - probably, it could be fixed in PCI subsystem using device_pm_move_after() or > device_move() in PCIe ports probe. > if yes - ... maybe we can scan/re-check and reorder dpm_list on suspend enter and > restore ("parent<-child" dependencies).
> Truth is that smth. need to be done 100%. Personally, I was hit by this issue also, > and it cost me 3 hours of debugging and I came up with the same patch as > Bill Huang, then spent some time trying to understand what is wrong with PCI > - finally, I've just changed the order of my devices in DT :) > > Also, I think, it will be good to have this patch in -next to collect more feedbacks.
I like the idea of forcing all probes during a sleep transition to be deferred. We could carry them out just before unfreezing the user threads. That combined with the change mentioned above ought to be worth testing.
Alan Stern
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