Alan Stern writes: > That's not what I'm saying. What I'm saying is that it would be a big > mistake to force all drivers which implement runtime PM to do it using > a separate code path from system PM. OK; I can accept that provided there is a way to change the "what to do with an I/O request" policy from auto-resume to something else while we're suspending the system (and presumably restore the old policy on system resume if the device was runtime-suspended at the point where the system was suspended). > > The main attraction of the late-suspend call is that it really does, > > reliably, guarantee that the driver's I/O request methods won't get > > called between the late-suspend call and the early-resume call. > > For some drivers (like USB), carrying out an actual suspend requires a > delay. Right now we implement those delays using wait_event(), > wait_for_completion(), and so on. Would you have us check at runtime > whether or not a system suspend is underway and in each case use a > busy-loop instead if it is? No; the late suspend call isn't appropriate for all drivers. It is a simple and safe way to do the suspend for some drivers, mostly the simpler ones. Things that are complex enough to have a subsystem (e.g. USB) would want to use the early suspend call. > What happens if, in order to carry out the late-suspend, a driver needs > to acquire a mutex which happens to be held by some other task? That > other task won't be able to run and release the mutex, so you will > deadlock. Then late-suspend is not appropriate for that driver, and it needs to use the early-suspend call, and do something such as setting a flag that the I/O request function tests. Paul. _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
