On Wed, 9 Dec 2009, Mark Brown wrote: > On Tue, Dec 08, 2009 at 09:35:59PM -0500, Alan Stern wrote: > > 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. > > There's some potential for this in embedded audio - it wants to bring > down the entire embedded audio subsystem at once before the individual > devices (and their parents) get suspended since bringing them down out > of sync can result in audible artifacts. Depending on the system the > suspend may take a noticable amount of time so it'd be nice to be able > to run it asynchronously, though we don't currently do so. For something like bringing down the entire embedded audio subsystem, which isn't directly tied to a single device, you would probably be better off doing it when the PM core broadcasts a suspend notification (see register_pm_notifier() in include/linux/suspend.h). This occurs before any devices are suspended, so synchronization isn't an issue. > At the minute we get away with this mostly through not being able to > represent the cases that are likely to actually trip up over it. > > > Interestingly, this non-tree dependency problem does not affect resume. > > Embedded audio does potentially - the resume needs all the individual > devices in the subsystem and can take a substantial proportion of the > overall resume time. Currently we get away with a combination of > assuming that all the drivers are live when we decide to start resuming > them and using the ALSA userspace API to deal with bringing the resume > out of line, but it's not ideal. You can do the same thing with the resume notifier. 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
