PowerManager Methods

[David Zeuthen]

On Sun, 2005-07-24 at 21:20 +0100, Richard Hughes wrote: 
> Okay, how do we approach the problem of acpi/pmu/apm specific scripts in
> HAL?
> 

I think I said it before but I'll say it again - we'll leave that to the
distros to sort out :-) - I'd love to have distros/vendors (Red Hat,
SUSE, Ubuntu, Debian, Gentoo etc.) rally around a common format but I
don't see that happening anytime soon. I've heard though that Ubuntu got
some good power management scripts :-). But see below too.

> Two ways I see as feasible:
> 
> 1. A script that is passed the acpi/apm/pmu information as part of it's
> command line (i.e. a multipurpose script)
> The FDI would match the different hibernate/suspend/restart methods with
> the power_management.can_hibernate keys (that are created in
> acpi.c/apm.c/pmu.c)
> 
> 2. Multiple scripts for each platform such as acpi-hibernate.sh that
> actually perform the action.
> This would mean we would potentially have 12 different scripts, but the
> scripts could be kept very small.
> 
> Assuming we have the key power_management.can_hibernate, where would it
> be set? From an FDI file or from acpi.c itself.
> 
> For testing I've been testing the presence of
> power_management.is_enabled and unconditionally adding the keys (so a
> user would modify the FDI file manually)
> 
> Doing it in the apm.c type files would allow us to be more selective on
> what each subsystem is capable of.
> 
> How should we do this?

I think the first thing to agree upon is the interface exported by HAL.
This will be the abstract vendor/distro neutral interface that desktop
apps, like gnome-power-manager, can rely on. What do we want this
interface to look like?

Here's an idea (in pseudo-code)

  interface org.freedesktop.Hal.Device.SystemPowerManagement {

    # Suspends the entire system. Puts the system in a state where
    # the session is kept in memory at a low power consumption
    # rate.
    #
    # @param wakeUpTime   number of seconds before the system wakes up
    #                     or 0 to not automatically wake up
    #
    # @raises             WakeupNotSupported, OperationFailed,
    #                     NotSupported
    #
    void Suspend(int wakeUpTime);

    # Hibernates the entire system. Puts the system in a state where
    # the session is stored on persistent media and the system can
    # be completely powered off.
    #
    # @param wakeUpTime   number of seconds before the system wakes up
    #                     or 0 to not automatically wake up
    #
    # @raises             WakeupNotSupported, OperationFailed, 
    #                     NotSupported
    #
    void Hibernate(int wakeUpTime);

    # This method is used to configure the operating system kernel
    # to sacrifice performance, and to a certain extent, data
    # integrity, in order to preserve power. It's useful to invoke
    # this method when the system transitions from running on AC
    # power to battery power and vice verca.
    #
    # @param lowPowerMode   Whether to put the system in low power
    #                       mode
    # 
    # @raises               OperationFailed, NotSupported
    # 
    void SetLowPowerMode(bool lowPowerMode);

  };

Also, we should have the following properties

 system_power_management.supports_suspend (bool)
 system_power_management.supports_hibernate (bool)
 system_power_management.supports_low_power_mode (bool)

so e.g. gnome-power-manager knows, a'priori, what is supported. We might
want a callout to set these values.

Once we agree on the interface we can talk about how to implement it; if
you want to do a wrapper [1] for the various distros out there and put
that in hal, fine by me :-)

(yea, I know that we already have policy.acpi.linux.can_suspend etc. but
I want to change the names so they match with the interface)

Btw I really really want this interface, and others, to be described in
the spec document

http://cvs.freedesktop.org/*checkout*/hal/hal/doc/spec/hal-spec.html

here; patches always welcome for updating this document from 0.4.x to
0.5.x - right now it's sort of inbetween =).

What do you think?

Cheers,
David

[1] : e.g. pm-suspend on Fedora; other commands on other distros etc.


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