[Bug 103781] New: Intel - display brightness control not working with i915.fastboot=1

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=103781

            Bug ID: 103781
           Summary: Intel - display brightness control not working with
                    i915.fastboot=1
           Product: DRI
           Version: XOrg git
          Hardware: Other
                OS: All
            Status: NEW
          Severity: normal
          Priority: medium
         Component: DRM/Intel
          Assignee: intel-gfx-bugs at lists.freedesktop.org
          Reporter: arthurborsboom at gmail.com
        QA Contact: intel-gfx-bugs at lists.freedesktop.org
                CC: intel-gfx-bugs at lists.freedesktop.org

Created attachment 135522
  --> https://bugs.freedesktop.org/attachment.cgi?id=135522&action=edit
dmesg when booted with the fastboot flag

Hardware: Asus N751JK laptop, i7-4710HQ
OS: Arch Linux
Kernel: 4.13.11
Kernel module: i915

While reading through a news article on Phoronix.com, I decided to test an
upcoming kernel/driver feature: Intel display 'fastboot'.

This can be activated by the kernel option i915.fastboot=1
This indeed speeds up the boot process and reduces the flickering, but with a
side effect. Normally I use the Fn-buttons to change the brightness of the
(laptop) screen. This works fine without the fastboot kernel parameter.

This does not work anymore with the kernel parameter. It seems to be stuck at
maximum brightness. When I press the reduce brightness button multiple times,
the screen turns black. When I press then only 1 time the increase brightness
button, the screen is back on at maximum brightness. 

dmesg when booted with the fastboot parameter is attached.

Is this misconfiguration, a bug or something else?
Do I need to provide more information and if so what?

Best regards,
Arthur Borsboom.

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