[Bug 214899] ideapad-laptop: platform backlight device not working

[bugzilla-daemon@bugzilla.kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=214899

Hans de Goede (jwrdegoede@fedoraproject.org) changed:

           What    |Removed                     |Added
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                 CC|                            |jwrdegoede@fedoraproject.or
                   |                            |g

--- Comment #2 from Hans de Goede (jwrdegoede@fedoraproject.org) ---
What is your kernel commandline?  According to your attached dmesg it is empty,
but that seems unlikely... ?

The ideapad-laptop code has this:

        if (acpi_video_get_backlight_type() == acpi_backlight_vendor) {
                err = ideapad_backlight_init(priv);
                if (err && err != -ENODEV)
                        goto backlight_failed;
        }

And acpi_video_get_backlight_type() is:

enum acpi_backlight_type acpi_video_get_backlight_type(void)
{
...
        if (acpi_backlight_cmdline != acpi_backlight_undef)
                return acpi_backlight_cmdline;

        if (acpi_backlight_dmi != acpi_backlight_undef)
                return acpi_backlight_dmi;

        if (!(video_caps & ACPI_VIDEO_BACKLIGHT))
                return acpi_backlight_vendor;

        if (acpi_osi_is_win8() && backlight_device_get_by_type(BACKLIGHT_RAW))
                return acpi_backlight_native;

        return acpi_backlight_video;
}

So the only way that the ideapad backlight can get registered is if:

1. You have acpi_backlight=vendor on your kernel cmdline
2. There is a DMI quirk setting for your model in the kernel which there is
not.
3. Your ACPI tables do not implement the ACPI_VIDEO_BACKLIGHT interface, but
your dmesg says:

[    2.237329] ACPI: video: Video Device [GFX0] (multi-head: yes  rom: no 
post: no)

So this is unlikely, it is still possible though that your DSDT implements the
ACPI video interface but not the backlight part (that would be a first). I
cannot tell since the ACPI video interface is not in the DSDT, it is likely
defined in one of the SSDT tables. Please attach a full acpidump.

Can you try specifying: "acpi_backlight=video" on the kernel commandline and
then do:

ls /sys/class/backlight

And copy and paste the output here. This cmdline option not only helps me debug
this, but it should also workaround your backlight issue :)

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