Ubuntu
xserver-xorg-video-intel package

  1. Bug #228399
  2. Comment #38

Comment 38 for bug 228399

Revision history for this message
Stefan Bader (smb) wrote :

The patch had to get reverted as it caused regressions for Intel video cards (see bug #423296). The problem is that without the KMS code, the patch just causes the acpi video driver never to get initialized and by that prevents backlight control. The fix of this bug was unfortunately just coincidental. Without te acpi video driver being initialized it could not cause a panic.

As for this bug, I remember some other cases which could be avoided by playing around with the contents of /proc/acpi/video/*/DOS. This controls whether the BIOS switches video modes and how.

Bit 1:0
        0: The system BIOS should not automatically switch (toggle) the active display output,
           but instead just save the desired state change for the display output devices in
           variables associated with each display output, and generate the display switch event.
           OSPM can query these state changes by calling the _DGS method.
        1: The system BIOS should automatically switch (toggle) the active display output, with
           no interaction required on the OS part. The display switch event should not be
           generated in this case.
        2: The _DGS values should be locked. It’s highly recommended that the system BIOS
           do nothing when hotkey pressed. No switch, no notification.
        3: The system BIOS should not automatically switch (toggle) the active display output,
           but instead generate the display switch event notify codes 0x82, 0x83, or 0x84.
           OSPM will determine what display output state should be set, and change the display
           output state without further involvement from the system BIOS.
Bit 2
        0: The system BIOS should automatically control the brightness level of the LCD when
           the power changes from AC to DC.
        1: The system BIOS should not automatically control the brightness level of the LCD
           when the power changes from AC to DC.

The documentation (ACPI spec 3.0a) states 1 the default state, but it might depend on the card.