On Friday, September 07, 2012, Aaron Lu wrote: > On Thu, Sep 06, 2012 at 11:53:34PM +0200, Rafael J. Wysocki wrote: > > On Thursday, September 06, 2012, Rafael J. Wysocki wrote: > > > On Monday, August 27, 2012, Aaron Lu wrote: > > > > Currently, when we are trying to get the power state of an acpi device, > > > > we will do the following: > > > > If device is not power manageable, init its power state as its parent or > > > > if it does not have a parent, init as D0; > > > > If device is power manageable, evaluate _PSC and then refine with > > > > acpi_power_get_inferred_state. > > > > > > > > But there exist some devices with _PSx defined, but no _PSC or _PRx. > > > > It is power manageable, but the above method to get power state does > > > > not cover this case and its power state will be UNKNOWN(255). > > > > > > > > So change the check of power manageable to whether _PSC and _PRx > > > > defined. > > > > > > > > Signed-off-by: Aaron Lu <aaron.lu@xxxxxxxxx> > > > > > > Applied to the linux-next branch of the linux-pm.git tree. > > > > > > I think it should go to -stable too and therefore it would be good to have > > > it in v3.6, so I'd like to push it to Linus for -rc5, if Len has no objections. > > > > On a second thought, perhaps the initial power state of those devices > > _should_ be "unknown", hmm? > > > > After all, we don't know what power state the device is in. > > Agree here but I think this is a safe assumption that on initial system > boot, all devices should be at D0. We have already assumed this fact if > the device is not power manageable and has no parent. That is mandated by the spec, though. > And this patch just changed the condition to not judging if power > manageable but if it has _PSC or _PRx, since we will use that to know > the device's power state, so I think using _PSC or _PRx as the > condition check is more precise. It is not clear if we can assume anything about the initial power states of devices having _PSx defined if they cannot be determined through _PSC or power resources. > > Is there any practical user-visible problem this causes to happen? > > Yes, on a test system, when I try to put a device into D3 cold and ACPI > will complain that I can't due to its parent is in a even lower power > state UNKNOWN(255), this parent device is power manageable but has no > _PSC and _PRx defined. Perhaps we can force _PS0 for such devices to start with, so that we know for sure that the initial state is D0? Rafael -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
