On Wednesday, December 15, 2010, ykzhao wrote: > On Wed, 2010-12-15 at 04:24 +0800, Rafael J. Wysocki wrote: > > On Tuesday, December 14, 2010, ykzhao wrote: > > > On Tue, 2010-12-14 at 05:25 +0800, Rafael J. Wysocki wrote: > > > > On Monday, December 13, 2010, ykzhao wrote: > > > > > On Sun, 2010-12-12 at 06:39 +0800, Rafael J. Wysocki wrote: ... > > > > The force_power_state was _only_ a workaround for the case when > > acpi_bus_set_power() called acpi_bus_get_power() and apparently received > > a wrong value from it on some systems (two of them had been identified, one was > > blacklisted in the end). However, after my changes acpi_bus_set_power() > > doesn't call acpi_bus_get_power() (or any equivalent) any more, so this > > workaround isn't necessary any more either. > > The flag of force_power_state will force it to do the transition of > power state even when the target state is already the same as the > current power state. Without this flag, it will skip the power > transition if the two states are consistent. This is useful under the > following cases: (The FAN device is used as an example) > 1. The initial state is reported as D0 state (But we don't know > whether the FAN device is really turned on) > 2. If we expect to turn on the corresponding FAN device for the > first time(put it into D0 state), it will skip the power transition as > the check of "state == device->power.state". In such case it will be > better that the power transition is forced in order to assure that the > FAN device is turned on by calling the _PSC/_ON object. Before my changes the force_power_state device flag was used only by the fan driver in two places: in acpi_fan_add() (ie. during fan initialization) and in acpi_fan_resume(). In both cases it was used to make acpi_bus_set_power() accept the state read by acpi_bus_get_power(). In both cases acpi_bus_update_power() can be used to obtain _exactly_ the same result, so the flag is not necessary any more. Thanks, Rafael _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
