Fwd: org.freedesktop.PowerManagement

Patryk Zawadzki patrys at pld-linux.org
Tue Mar 27 04:25:56 PDT 2007

On 3/27/07, Danny Kukawka <dkukawka at suse.de> wrote:
> On Dienstag, 27. März 2007, Richard Hughes wrote:
> > First, there might be more than a single backlight
> - the tool which provide the interface have to handle this or the get/set
> methodes have to take/return arrays with info for each display. But the major
> use case on laptops this is IMO not really needed, there is the internal
> display the thing you want to change

Arrays? Maybe add another param that is the HAL ID of the device to
both get and set and add a method to easily enumerate the devices
(return an array of all known IDs and names).

> > Secondly, exporting the brightness as percentage sucks
> No, it does not. It make no sense to export e.g. all ~250 brightnesslevel of a
> Panasonic laptop display. If you want to change the display brightness of
> such a display e.g. with a slider in the GUI you produce high system load and
> many calls to HAL/in HAL. And you can't see the difference between level 170
> and 172.

But it does suck if your LCD only supports ~17 brightness levels and
calculating percentage gives you fractions. How do you handle
brightness up/down controls there?

- Internally keep the current counter and each time it changes map it
to the closest handled by LCD?

- Each time it changes reset it to the closest value (would require
the application to incrementally try to increase brightness untill
there is a change)

> Mapping the existing level to percentage make much sense. This allow you also
> to use your settings on different machines with different brightness level
> (if you use e.g. a NFS home).

It should be kept as a per-device setting, not global. What if I have
a really bright LCD at one location/machine and a really dim one at
the other?

> Btw. the mapping to percentage should maybe happen in HAL directly.

I think this really belongs to the GUI part of the application, not
the hardware abstraction.

> > Move the backlight stuff to their own D-Bus
> > objects: /org/freedesktop/PowerManagement/BackLighDevices/backlight0 and so
> > on. (better use some HAL device name for naming the object)
> Make maybe sense, but why do we need these new interfaces which are somehow
> only duplicates of the HAL stuff? Would it not make more sense to only
> provide one interface to all display backlights (set brightness to 50% would
> set it to all displays) or only to the primary display (would make sense on
> laptops)? For all other interfaces you can use HAL also directly or not?

It makes sense only for laptops. What if I use an UPS and want all the
monitors but the main one to either turn off or get as low in
brightness as possible in case of power failure?

Or I don't want to touch the one that has an auxiliary power source?

Patryk Zawadzki
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