[Bug 97883] New: [i915] intel_backlight does not function - Lenovo X1 Yoga OLED

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=97883

            Bug ID: 97883
           Summary: [i915] intel_backlight does not function - Lenovo X1
                    Yoga OLED
           Product: DRI
           Version: DRI git
          Hardware: Other
                OS: All
            Status: NEW
          Severity: normal
          Priority: medium
         Component: DRM/Intel
          Assignee: intel-gfx-bugs at lists.freedesktop.org
          Reporter: dan at ified.ca
        QA Contact: intel-gfx-bugs at lists.freedesktop.org
                CC: intel-gfx-bugs at lists.freedesktop.org

Created attachment 126688
  --> https://bugs.freedesktop.org/attachment.cgi?id=126688&action=edit
Full dmesg output with drm.debug=0x1e log_buf_len=1M

On the OLED version of the Lenovo X1 Yoga, the intel_backlight device reports a
range of 0 to 852, but its setting has no effect. (Perhaps not too surprising
since this device technically has no backlight.) The display brightness is
always (near?) maximum when Linux is booted.

The thinkpad_acpi module does no better at providing brightness controls.

The xrandr --brightness setting is a nearly-adequate workaround, but is
occasionally reset while using X.org normally (I have not investigated the
cause yet).

Attached logs are from an Ubuntu kernel-ppa image, stamped:
  cod/tip/drm-intel-next/2016-09-20 (6e05f3d3b9298a56d6f1acb474a75cf14a17c31e)

The laptop display is attached to eDP1. There is a second display attached to
DP1; I can provide logs without that if requested.

I was not able to create a vbios dump. ("Input/Output error")

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