On Tue, 8 Dec 2009, Linus Torvalds wrote: > It's just that I think the "looping over children" is ugly, when I think > that by doing it the other way around you can make the code simpler and > only depend on the PM device list and a simple parent pointer access. I agree that it is uglier. The only advantage is in handling asynchronous non-tree suspend dependencies, of which we probably won't have very many. In fact, I don't know of _any_ offhand. Interestingly, this non-tree dependency problem does not affect resume. > I also think that you are wrong that the above somehow protects against > non-topological dependencies. If the device you want to keep delay > yourself suspending for is after you in the list, the down_read() on that > may succeed simply because it hasn't even done its down_write() yet and > you got scheduled early. You mean, if A comes before B in the list and A must suspend after B? Then A's down_read() on B _can't_ occur before B's down_write() on itself. The down_write() on B happens before the list_for_each_entry_reverse() iteration reaches A; it even happens before B's async task is launched. > But I guess you could do that by walking the list twice (first to lock > them all, then to actually call the suspend function). That whole > two-phase thing, except the first phase _only_ locks, and doesn't do any > callbacks. Not necessary. Alan Stern -- 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
