[Bugme-new] [Bug 41672] New: backlight control will not work on Lenovo V570

bugzilla-daemon at bugzilla.kernel.org bugzilla-daemon at bugzilla.kernel.org
Wed Aug 24 12:25:15 PDT 2011


https://bugzilla.kernel.org/show_bug.cgi?id=41672

           Summary: backlight control will not work on Lenovo V570
           Product: ACPI
           Version: 2.5
    Kernel Version: 3.1-rc3 and others
          Platform: All
        OS/Version: Linux
              Tree: Mainline
            Status: NEW
          Severity: normal
          Priority: P1
         Component: ACPICA-Core
        AssignedTo: acpi_acpica-core at kernel-bugs.osdl.org
        ReportedBy: wfp5p at virginia.edu
        Regression: No


No backlight options will be available on a Lenovo V570.  I've tried it with
several different kernel versions including 3.1-rc3.  In all cases dmesg has
the error  ACPI Error: Current brightness invalid. 

It appears the kernel believes the machine is multi-headed.  It does the right
thing for the first head it sees and then gets the invalid brightness on the
second head which causes it to assume acpi brightness won't work.  The laptop
has the standard external D-sub connector for an external monitor, but there is
nothing connected to it.  In fact, if I make the ugly hack of commenting out
the multihead check in acpi_video_bus_check() then backlight control works
fine.

I'll attach the acpidump, dmesg, and ugly hack.

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