On 01/09/2014 05:21 AM, Alan Stern wrote: > On Wed, 8 Jan 2014, Phillip Susi wrote: >> You issue a REQUEST SENSE command and that returns status indicating >> whether the drive is stopped, or in standby. See my patches. One of > > I never saw your patches. Where were they posted? > > If you issue the REQUEST SENSE command in the usual way (going through > the SCSI and block layers), and the disk is already in runtime suspend, > it won't do what you want. The block layer won't deliver requests > until the device leaves the RPM_SUSPENDED state. In addition, when it > receives the command the block layer will submit a deferred > runtime-resume request, which rather defeats the whole purpose. > > (I guess you actually saw some of this happen, and that's what led to > this email thread in the first place.) > > 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. -- 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
