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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