Am Mittwoch 13 August 2008 17:44:00 schrieb Stefan Richter: > Oliver Neukum wrote: > > Am Mittwoch 13 August 2008 16:59:23 schrieb Alan Stern: > [Quoting Oliver: true SCSI busses can be shared. So are we using the > correct approach?] > >> This is a good question. Most USB mass-storage devices do not act as a > >> true SCSI bus, but I believe there are a few non-standard ones that do > >> -- the USB device really contains a SCSI host and arbitrary SCSI > > > > OK, but does it make sense to have SCSI autosuspend? Or should autosuspend > > operate on the bus the _host_ is connected to (usb, pci, ...)? > > In Alan's patch, SCSI calls scsi_host_template methods (if the LLD > provides ones) to suspend and resume a Scsi_Host. The LLD can use them > to work with the underlying infrastructure to determine what can be done > at that time. I.e. are there other protocols or other initiator-like > nodes sharing the link? If yes or if "maybe yes", the infrastructure > keeps the link up. If not, it can move it into a low-power state. That is a parculiar way of viewing it. Alan's patch introduce runtime pm attributes to the devices. Quoting: +/** + * scsi_suspend_sdev - suspend a SCSI device + * @sdev: the scsi_device to suspend + * @msg: Power Management message describing this state transition + * + * SCSI devices can't actually be suspended in a literal sense, + * because SCSI doesn't have any notion of power management. Instead + * this routine drains the request queue and calls the ULD's suspend + * method to flush caches, spin-down drives, and so on. + * + * If the suspend succeeds, we call scsi_autosuspend_host to decrement + * the host's count of unsuspended devices and invoke the LLD's suspend + * method. So you cannot operate on the link independent from the devices. Regards Oliver _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
