On Tuesday, September 13, 2016 09:21:23 AM Marek Szyprowski wrote: > Hi Rafael, > > > On 2016-09-12 23:25, Rafael J. Wysocki wrote: > > On Monday, September 12, 2016 04:07:27 PM Lukas Wunner wrote: > >> On Thu, Sep 08, 2016 at 11:29:48PM +0200, Rafael J. Wysocki wrote: > >>> Introduce a new flag in struct dev_pm_info, pm_sleep_in_progress, to > >>> indicate that runtime PM has been disabled because of a PM sleep > >>> transition in progress. > >> [...] > >>> That will allow helpers like pm_runtime_get_sync() to be called > >>> during system sleep transitions without worrying about possible > >>> error codes they may return because runtime PM is disabled at > >>> that point. > >> I have a suspicion that this patch papers over the direct_complete bug > >> I reported Sep 10 and that the patch is unnecessary once that bug is > >> fixed. > > It doesn't paper over anything, but it may not be necessary anyway. > > > >> AFAICS, runtime PM is only disabled in two places during the system > >> sleep process: In __device_suspend() for devices using direct_complete, > >> and __device_suspend_late() for all devices. > >> > >> In both of these phases (dpm_suspend() and dpm_suspend_late()), the > >> device tree is walked bottom-up. Since we've reordered consumers to > >> the back of dpm_list, they will be treated *before* their suppliers. > >> Thus, runtime PM is disabled on the consumers first, and only later > >> on the suppliers. > >> > >> Then how can it be that runtime PM is already disabled on the supplier? > > Actually, I think that this was a consequence of a bug in > > device_reorder_to_tail() > > that was present in the previous iteration of the patchset (it walked > > suppliers > > instead of consumers). > > > >> The only scenario I can imagine is that the supplier chose to exercise > >> direct_complete, thus was pm_runtime_disabled() in the __device_suspend() > >> phase, and the consumer did *not* choose to exercise direct_complete and > >> later tried to runtime resume its suppliers and itself. > >> > >> I assume this patch is a replacement for Marek's [v2 08/10]. > >> @Marek, does this scenario match with what you witnessed? > > It is not strictly a replacement for it. The Marek's patch was the > > reason to post it, but I started to think about this earlier. > > > > Some people have complained to me about having to deal with error codes > > returned by the runtime PM framework during system suspend, so I thought > > it might be useful to deal with that too. > > > > That said it probably is not necessary right now. > > I've tested this patchset without this patch and system sleep with > device link > enabled worked fine. However this might be also a consequence of > enabling runtime > pm during system sleep since v4.8-rc1. > > It looks that for now this patch can be skipped until a real use case for it > appears.
OK, thanks!
