On Tue, Sep 11, 2012 at 10:38:06PM +0200, Rafael J. Wysocki wrote:
> It turns out that there are ACPI BIOSes defining device objects with
> _PSx and without either _PSC or _PRx. For devices corresponding to
> those ACPI objetcs __acpi_bus_get_power() returns ACPI_STATE_UNKNOWN
> and their initial power states are regarded as unknown as a result.
> If such a device is a parent of another power-manageable device, the
> child cannot be put into a low-power state through ACPI, because
> __acpi_bus_set_power() refuses to change power states of devices
> whose parents' power states are unknown.
>
> To work around this problem, observe that the ACPI power state of
> a device cannot be higher-power (lower-number) than the power state
> of its parent. Thus, if the device's _PSC method or the
> configuration of its power resources indicates that the device is
> in D0, the device's parent has to be in D0 as well. Consequently,
> if the parent's power state is unknown when we've just learned that
> its child's power state is D0, we can safely set the parent's
> power.state field to ACPI_STATE_D0.
>
> Signed-off-by: Rafael J. Wysocki <rjw@xxxxxxx>
Tested-by: Aaron Lu <aaron.lu@xxxxxxxxx>
-Aaron
> ---
> drivers/acpi/bus.c | 10 ++++++++++
> 1 file changed, 10 insertions(+)
>
> Index: linux/drivers/acpi/bus.c
> ===================================================================
> --- linux.orig/drivers/acpi/bus.c
> +++ linux/drivers/acpi/bus.c
> @@ -237,6 +237,16 @@ static int __acpi_bus_get_power(struct a
> } else if (result == ACPI_STATE_D3_HOT) {
> result = ACPI_STATE_D3;
> }
> +
> + /*
> + * If we were unsure about the device parent's power state up to this
> + * point, the fact that the device is in D0 implies that the parent has
> + * to be in D0 too.
> + */
> + if (device->parent && device->parent->power.state == ACPI_STATE_UNKNOWN
> + && result == ACPI_STATE_D0)
> + device->parent->power.state = ACPI_STATE_D0;
> +
> *state = result;
>
> out:
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