On Thursday, September 7, 2017 8:56:07 AM CEST Ulf Hansson wrote: > On 7 September 2017 at 00:14, Rafael J. Wysocki <rjw@xxxxxxxxxxxxx> wrote: > > Hi, > > > > It occurred to me earlier today that it should be possible to modify the > > PM core to get the functionality of pm_runtime_force_suspend/resume() from it > > in a somewhat nicer way which should be possible to extend to middle layers > > (bus types, PM domains etc). > > > > Say we have a flag telling the PM core to use the runtime PM path at the > > late suspend and early resume stages of system suspend/resume directly if > > it can't find "proper" callbacks for that. It is called DPM_FLAG_USE_RPM in > > the prototype patch below. > > > > The idea is to set only ->runtime_suspend and ->runtime_resume in the driver's > > dev_pm_ops and then set that flag in ->probe and be done. If the core sees > > the flag and doesn't see any "original" system sleep callbacks at the stages > > in question, it will automatically switch over to the runtime PM path and > > leave the device alone if it is already runtime-suspended. > > > > One nice thing about it is that it will happen at the core level and not in > > a driver callback, so all of the concerns regarding layering violations are > > simply not relevant any more. Also, at least in principle, it should be > > possible to extend this to middle layers that need to do some non-trivial PM > > handling, simply by making them look at that flag and honor in the same way > > as the core does that. This way drivers may still be able to reuse their > > runtime PM stuff for handling system sleep transitions even if the middle > > layers they need to work with have different things to do for runtime PM > > and system suspend/resume. Even modifying *all* middle layers in the tree to > > do take DPM_FLAG_USE_RPM into accout if set is not out of the question as far > > as I'm concerned. > > > > On top of this it should be possible to add the optimization allowing devices > > to stay suspended after system resume even if they were not suspended before. > > IMO it is better to add a separate flag for enabling it in case some drivers > > don't want it, though. > > > > So the below is just the core part and mostly a prototype to illustrate the > > idea, but at this point it looks promising to me. > > > > Comments? Concerns? > > Yes, a couple so far. > > 1) I like the overall idea, which means the PM core gets the knowledge > of what to do, based on some instructions by the driver. Yeah, it's a > great idea I think. > 2) We need also a way to allow drivers to deal with additional > operations during system suspend (and resume etc), besides making it > possible to re-use the RPM callbacks to put the device into a low > power state. Could we allow the system sleep callbacks to be present > as well when using this flag? Yes, we could. It's perfectly fine to do that with the patch I posted. One can even provide ->suspend_late or ->resume_early and set this flag even though that wouldn't make a lot of sense. :-) > Let's bring up this also at LPC next week, we can make it a part of > the ACPI slot, if needed. Agreed, and we will. Thanks, Rafael -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
