On Wed, 2012-09-19 at 14:50 +0200, Rafael J. Wysocki wrote: > On Wednesday, September 19, 2012, James Bottomley wrote: > > On Wed, 2012-09-19 at 16:03 +0800, Aaron Lu wrote: > > > Hi James, > > > > > > May I know if this patchset will enter v3.7? > > > > Sigh, well, I was hoping to persuade the PM people to sort this out > > first. > > > > The first observation is that all this looks to be too specific. ZPO > > may be ACPI specific, but the property it abstracts: whether the > > particular device is powered off or not is generic and probably should > > be known at the generic PM level. Nothing actually really cares about > > how we power off the device until you get all the way down to the ACPI > > controller. > > > > I think we could do this with a couple of flags sitting inside struct > > device itself: one for pm state and capabilities defined at a generic > > level and one for device specific pm state. The latter would be for > > things like the door lock information which is very specific to CDs > > (although not specific to SCSI CDs). Alternatively, even if we can't > > use these capabilities at the generic pm level, we still need an > > internal state set of flags because power state stuff traverses the > > stack and struct device is the only universal object in that stack. > > > > So I definitely think all of the sdev flags should become either generic > > or specific flags in device. > > Well, the problem is that it is kind of irrelevant to the core whether or > not the given device can be powered off. Moreover, the actual meaning of > what "power off" means depends on the platform (it may be an individual device > state or a power domain state, for instance). Also, the set of available > low-power states depends on the platform (or the bus type) and generally > cannot be universally represented and there are low-power states that > aren't "power off" per se, but still require the device state to be > restored when putting it back into full power. So I don't insist on it being generic, but we do need somewhere to hang the state. > We've discussed that for a few times and each time we've ended up agreeing > that struct device is not the right place to store this information (for > example, PCI stores it in struct pci_dev, USB has its own rules etc.). So, here's the problem this causes. In SCSI, lower level devices have no access to the drivers (to which the upper layer structures are tied), so we have no way to go from device/scsi device to the scsi_disk structure say. This means that a lot of device specific PM stuff tends to have flags in scsi_device just so we can get access to it. A flag in device would allow us to carry the information farther (say to struct cdrom for instance). > I'll have a look at the patchset again and see what can be done about this. Thanks, James -- 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
