On Thu, 9 Jan 2014, Aaron Lu wrote: > > It's a knotty situation. The only way to find out whether the disk is > > spinning is to ask it, which requires doing I/O, which requires > > spinning up the disk. Maybe we need to add a mechanism to the block > > layer's runtime PM implementation for addressing just this situation. > > I think it's knotty because the runtime PM status is a view from the > kernel/host side, i.e. it is runtime suspended if it is not being used, > no matter which power state it is in. The trigger for the PM state > transition are all based on this, if we want to do it the other way > around(update device's runtime PM status based on device's actual power > state), we are in a knotty situation. No, that's not the problem. The problem is that the block layer does not permit any requests to go through if the queue's rpm_status is RPM_SUSPENDED. We should change the code in the block layer. blk_pm_peek_request should allow requests with REQ_PM set to go through, no matter what the rpm_status is. Then the disk driver could query the disk (to see whether it is spinning) while the disk remains in runtime suspend. Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-ide" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
