On Fri, 20 May 2016 15:17:20 +0800, Aaron Lu said:
> On Fri, May 20, 2016 at 03:02:08AM -0400, Valdis.Kletnieks@vt.edu wrote:
> > With the patches reverted:
> > 
> > [/sys/class/backlight/acpi_video0] grep . *bright*
> > actual_brightness:95
> > brightness:95
> > max_brightness:95
> > 
> > And the weird part inside the kernel - on a kernel that has the problem,
> > /sys/class/backlight is *empty* - only '.' and '..' entries.
> > 
> > No, I don't understand why the acpi_video0 entry isn't created when that
> > commit is in place.
>
> The commit probably makes acpi_video_init_brightness bail out for some
> reason, adding debug prints under those "if (result)" in
> acpi_video_init_brightness should help to identify where it goes wrong.
>
> And your acpidump please, thanks.

The dmesg output:

[    1.966400] ACPI: Power Button [PWRF]
[    1.969759] ACPI: Video Device [VID] (multi-head: yes  rom: yes  post: no)
[    1.969829] acpi_evaluate_BCL failed, 4097
[    1.969866] acpi_evaluate_BCL failed, 4097
[    1.969898] acpi_evaluate_BCL failed, 4097
[    1.969930] acpi_evaluate_BCL failed, 4097
[    1.969961] acpi_evaluate_BCL failed, 4097
[    1.969994] acpi_evaluate_BCL failed, 4097
[    1.970045] acpi_evaluate_BCL failed, 4097
[    1.970077] acpi_evaluate_BCL failed, 4097
[    1.970621] acpi_evaluate_BCL failed, 5
[    1.970652] Could not query available LCD brightness level
[    1.970692] acpi_video_get_levels failed, -19
[    1.973516] ACPI Error: Current brightness invalid (20160422/video-368)
[    1.973528] acpi_video_bqc_quirk failed, -22
[    1.973567] acpi_evaluate_BCL failed, 5
[    1.973597] Could not query available LCD brightness level
[    1.973636] acpi_video_get_levels failed, -19
[    1.973672] acpi_evaluate_BCL failed, 5
[    1.973701] Could not query available LCD brightness level
[    1.973741] acpi_video_get_levels failed, -19
[    1.973777] acpi_evaluate_BCL failed, 5
[    1.973807] Could not query available LCD brightness level
[    1.973847] acpi_video_get_levels failed, -19
[    1.973882] acpi_evaluate_BCL failed, 5
[    1.973911] Could not query available LCD brightness level
[    1.973951] acpi_video_get_levels failed, -19
[    1.973986] acpi_evaluate_BCL failed, 5
[    1.974439] Could not query available LCD brightness level
[    1.974479] acpi_video_get_levels failed, -19
[    1.974529] acpi_evaluate_BCL failed, 5
[    1.974565] Could not query available LCD brightness level
[    1.974603] acpi_video_get_levels failed, -19
[    1.977783] input: Video Bus as /devices/LNXSYSTM:00/LNXSYBUS:00/PNP0A08:00/device:14/LNXVIDEO:00/input/input4
[    1.980879] thermal LNXTHERM:00: registered as thermal_zone0
[    1.980884] ACPI: Thermal Zone [THM] (64 C)

acpidump is attached...