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[Volker Knollmann <v.knollmann@xxxxxx>]

Hmmm... weird... I just found out that correct display brightness is
restored on resume if the laptop is NOT CONNECTED to the AC power. So
the problem does not occur when resuming on battery power.

@Philippe:
Can you confirm this behaviour with our own system?

I have no idea about the detailed technical background, so I'm just guessing:
Is there some kind of trigger/event/interrupt from ACPI missing/ignored when resuming on AC power? Some trigger like "Hey, adjust your display brightness!!".
During normal operation such an event seems to be fired when disconnecting AC power, since the display is slightly dimmed. Maybe it's exactly this function "detect transition from AC to battery ==> set brightness" that runs at the very moment the laptop wakes up with AC power disconnected. That would explain why the brightness is restored in that special case.


This is just my own theory... since I'm not burdened with any technical expertise chances are high that it's complete bullsh*t... ;-)

Best regards,
Volker

-- 
[i965GM] Display brightness completely dimmed after waking up from suspend
https://bugs.launchpad.net/bugs/417610
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