On Friday, 28 September 2007 16:33, Alan Stern wrote: > On Fri, 28 Sep 2007, Oliver Neukum wrote: > > > > > > What exactly would you like to do? > > > > > > > > Put the stuff into struct device and move the autosuspend code into > > > > driver core. > > Moving some of the data fields might be acceptable. Moving the code is > premature at best. You must always bear in mind that the autosuspend > model used by USB is not suitable for every type of device. Each > subsystem needs to implement its own form of runtime PM; the core > should contain only the lowest-denominator common parts. Well, that's what I've been always thinking. > > > Well, I thought that it would be nicer if drivers handled autosuspend in a > > > transparent (from the point of view of the core) way. > > > > That is possible only for drivers which are leaves in the device tree. > > Not true. For example, the USB hub driver handles autosuspend > perfectly well. The main issue is what to do when the autosuspend > notifications need to cross a subsystem boundary. > > > > Now, it seems to follow from what you're saying that this is not possible in > > > general, because of USB mass storage devices that need some special handling. > > > > No, they need the ordinary handling. All a device's children must be suspended > > if a device is suspended. > > > > > I'm not familiar with the USB code, so can you please tell me how the USB > > > autosuspend is handled at present and what exactly the problem with that is? > > > > The drivers for interfaces manage a count. If all a device's interfaces' count > > goes to zero, the device is suspended. The drivers are notified through the > > normal suspend() method. But children of these devices are not notified. > > That's because the notifications go up the device tree, not down. When > a child is suspended, the parent is notified. Then if the driver sees > that all the children are suspended, the parent can be suspended as > well. > > Oliver has been trying to subvert this model by making usb-storage > responsible for suspending the SCSI disk and CD/DVD drivers, which are > located beneath it in the device tree. I've been trying to convince > him that the proper way to handle things is to let the SCSI drivers > decide for themselves when their devices can be suspended, and then > have them inform usb-storage. Yes, I think that the SCSI layer should decide. I guess that the SCSI layer is not really autosuspend-aware, is it? Greetings, Rafael _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
