More advanced power savings (rev. the DPMS extension).

[Keith Packard]

On Wed, 2006-07-26 at 12:48 -0700, Jay Cotton wrote:

> There are four power levels specified by the Video Electron-
> ics  Standards  Association  (VESA) Display Power Management
> Signaling (DPMS) standard.  These are mapped onto the X FBPM
> Extension like this:
> 
>   0            FBPMModeOn          In                    use
>   1            FBPMModeStandby     In      standby     mode.
>   2            FBPMModeSuspend     In     suspend      mode.
>   3            FBPMModeOff         Shut     off,    awaiting
> activity

I don't see any substantive difference between this extension and our
existing DPMS extension in terms of controlling the power levels in the
monitor. We should, instead, work to unify the core screen saver, DPMS,
FBPM and Screen Saver extensions into something usable by applications.
Adding another extension to this already horrible mess doesn't appear
helpful to me...

Some ideas:

 1) Existing external screen savers don't want the server to do anything
automatically. All power state transitions should be mediatable by an
external client.

 2) Power saving != screen blanking. Backlight levels dominate power use
by LCD screens, so a useful power saving mode is reduced backlight
level, which doesn't blank the screen. We should probably just expose
the backlight level through the X server and let the screen saver frob
that if it likes. Similarly, the OLPC color/mono switch could be made
visible as a power saving mode, but it may be that we should let that be
exposed through a separate extension as it is significantly different
than the normal power saving mechanisms.

 3) I don't think the OLPC internal/external FB switching should be
visible to the user; it sounds like there is a 15-45ms lag when
switching between the two frame buffers, which is well under the usual
100ms interactivity limit. As this can be entirely transparent to the
user, it should be.

-- 
keith.packard at intel.com
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