On Fri, 2022-09-23 at 15:48 +0200, Ulf Hansson wrote: > On Fri, 23 Sept 2022 at 14:47, Liu Ying <victor.liu@xxxxxxx> wrote: > > > > After a device transitions to sleep state through it's system > > suspend > > callback pm_runtime_force_suspend(), the device's driver may still > > try > > to do runtime PM for the device(runtime suspend first and then > > runtime > > resume) although runtime PM is disabled by that callback. The > > runtime > > PM operations would not touch the device effectively and the device > > is > > assumed to be resumed through it's system resume callback > > pm_runtime_force_resume(). > > This sounds like a fragile use case to me. In principle you want to > allow the device to be runtime resumed/suspended, after the device > has > already been put into a low power state through the regular system > suspend callback. Normally it seems better to prevent this from > happening, completely. Not sure if we really may prevent this from happening completely. > > That said, in this case, I wonder if a better option would be to > point > ->suspend_late() to pm_runtime_force_suspend() and ->resume_early() > to > pm_runtime_force_resume(), rather than using the regular > ->suspend|resume() callbacks. This should avoid the problem, I think, > no? I thought about this and it actually works for my particular panel-simple case. What worries me is that the device(DRM device in my case) which triggers the runtime PM operations may also use ->suspend_late/resume_early() callbacks for whatever reasons, hence no fixed order to suspend/resume the two devices(like panel device and DRM device). Also, not sure if there is any sequence issue by using the ->suspend_late/resume_early() callbacks in the panel-simple driver, since it's written for quite a few display panels which may work with various DRM devices - don't want to break any of them. Regards, Liu Ying > > Note that, the PM core also disables runtime PM for the device in > __device_suspend_late(). For good reasons. > > [...] > > Kind regards > Uffe
