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New: 2.6.25-rc1 regression - IBM ACPI backlight controlls do not work

Bugme-new Andrew Morton 3 participants 3 messages Feb 15, 2008 1 message not in the archive ACPI

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Andrew Morton

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#1 lore raw
Quoted 26 lines · On Fri, 15 Feb 2008 04:51:15 -0800 (PST) [email protected] wrote:

http://bugzilla.kernel.org/show_bug.cgi?id=9995

           Summary: 2.6.25-rc1 regression - IBM ACPI backlight controlls do
                    not work
           Product: ACPI
           Version: 2.5
     KernelVersion: 2.6.25-rc1
          Platform: All
        OS/Version: Linux
              Tree: Mainline
            Status: NEW
          Severity: normal
          Priority: P1
         Component: BIOS
        AssignedTo: [email protected]
        ReportedBy: [email protected]

Latest working kernel version: 2.6.24
Earliest failing kernel version: 2.6.25-rc1
Distribution: Ubuntu/Hardy
Hardware Environment: ThinkPad T61
Software Environment: n/a
Problem Description: /sys/class/backlight/acpi_video0 does not control backlight, nothing happens if I change brightness.

Quoted 3 lines

Steps to reproduce: echo {15,5,0} > /sys/class/backlight/acpi_video0/brightness nothing happens.

I've lost the plot on what's happening with backlight. I think you're about to find that this is not-a-bug, even though it stopped working.

#2 lore raw
Quoted 2 lines · Andrew Morton

I've lost the plot on what's happening with backlight. I think you're about to find that this is not-a-bug, even though it stopped working.

Why do you think that it is not-a-bug even if it stopped working? I don't think it is a feature as acpi video driver should control backlight levels on laptop that provides generic ACPI based backlight support which is the case of ThinkPad T61. Or at least it used to be with up to 2.6.24 kernels.

I can read sane values from /sys/class/backlight/acpi_video0/* but changing them has no effect on the backlight.

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Lukáš Hejtmánek
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