On Mon, 7 Jan 2008, Oliver Neukum wrote: > Am Montag, 7. Januar 2008 22:34:52 schrieb Alan Stern: > > On Mon, 7 Jan 2008, Oliver Neukum wrote: > > > > > Am Montag, 7. Januar 2008 20:42:23 schrieb Alan Stern: > > > > When all the devices under a host are suspended, the LLD is informed > > > > (via a new "autosuspend" method in the host template) so that it can > > > > > > That is most certainly a mistake. > > > > Why? > > You'll have to add this method whenever a new subsystem is affected > by power management. Sorry, I don't understand your point. If you mean that we'll have to add autosuspend and autoresume code to every driver that wants to support autosuspend, I agree. There doesn't seem to be any way around it. Note that the code added by the companion usb-storage patch is pretty small. > Besides what are the semantics of this method? The semantics are simple. The SCSI midlayer calls the autosuspend method when all the host's devices are suspended and the host's usage count becomes <= 0 (redundant, since each non-suspended device contributes to the usage count). The midlayer calls the autoresume method whenever the host's usage count rises from 0 to 1. (There are a few exceptions, such as when the host is being removed. We don't have to worry about them now.) To put it another way, the autosuspend method tells the LLD that it _may_ autosuspend the host adapter, not that it _must_. However the autoresume method does mean that the LLD _must_ attempt an immediate autoresume (the attempt is allowed to fail). > May suspend() be called after autosuspend() ? Your question contains a layering violation: The SCSI host template doesn't contain a suspend method. Do you mean to ask whether, for example, a PCI host adapter driver's PCI-suspend method could be called after its SCSI-autosuspend method? In general yes, but it depends on exactly what the autosuspend method does. > If not, will resume() be > called or autoresume() ? Let's take USB as a representative example (since it is the _only_ example at the moment). The SCSI core will call usb-storage's autosuspend method when the SCSI device is suspended. In turn, the method calls usb_autopm_put_interface(). This starts a timer that will, after 2 seconds, call usb-storage's suspend method and actually suspend the USB port. Or consider what happens during a system resume. The PM core will first resume the USB device, which causes usb-storage's resume method to be invoked. A little later the PM core will resume the SCSI device, which is lower in the device tree. This will cause the SCSI midlayer to call usb-storage's autoresume method, which will call usb_autopm_get_interface() -- thereby preventing the USB device from autosuspending 2 seconds after it was resumed. Does that answer your questions? Alan Stern - To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
