On Tuesday, October 17, 2017 10:12:19 PM CEST Alan Stern wrote: > On Tue, 17 Oct 2017, Ulf Hansson wrote: > > > > These functions are wrong, however, because they attempt to reuse the > > > whole callback *path* instead of just reusing driver callbacks. The > > > *only* reason why it all "works" is because there are no middle layer > > > callbacks involved in that now. > > > > > > If you changed them to reuse driver callbacks only today, nothing would break > > > AFAICS. > > > > Yes, it would. > > > > First, for example, the amba bus is responsible for the amba bus > > clock, but relies on drivers to gate/ungate it during system sleep. In > > case the amba drivers don't use the pm_runtime_force_suspend|resume(), > > it will explicitly have to start manage the clock during system sleep > > themselves. Leading to open coding. > > I think what Rafael has in mind is that the PM core will call the amba > bus's ->suspend callback, and that routine will then be able to call > the amba driver's runtime_suspend routine directly, if it wants to -- > as opposed to going through pm_runtime_force_suspend. Right in general. > However, it's not clear whether this fully answers your concerns. Well, in the particular AMBA case fixing this should be quite straightforward. > > Second, it will introduce a regression in behavior for all users of > > pm_runtime_force_suspend|resume(), especially during system resume as > > the driver may then end up resuming the device even in case it isn't > > needed. I believe I have explained why, also several times by now - > > and that's also how far you could take the i2c designware driver at > > this point. > > > > That said, I assume the second part may be addressed in this series, > > if these drivers convert to use the "driver PM flags", right? > > Presumably. > > The problem is how to handle things which need to be treated > differently for runtime PM vs. system suspend vs. hibernation. If > everything filters through a runtime_suspend routine, that doesn't > leave any scope for handling the different kinds of PM transitions > differently. Instead, we can make the middle layer (i.e., the bus-type > callbacks) take care of the varying tasks, and they can directly invoke > a driver's runtime-PM callbacks to handle all the common activities. > If that's how the middle layer wants to do it. Well, that's what happens today, except that driver runtime PM callbacks are not directly invoked. Actually, I tried to implement that, but it was so ugly and fragile that I gave up. It really is better if drivers point the different callback pointers to the same rountine if they want to reuse it. > > However, what about the first case? Is some open coding needed or your > > think the amba driver can instruct the amba bus via the "driver PM > > flags"? > > PM flags won't directly be able to cover things like disabling clocks. > But they could be useful for indicating explicitly whether the code to > take care of those things needs to reside at the driver layer or at the > bus layer. Right. Thanks, Rafael
