[Bug 106228] amdgpu reads back brightness 0 (which is not true) if checked before a brightness has been explicitly set - bugzilla-daemon

From: bugzilla-daemon@freedesktop.org
To: dri-devel@lists.freedesktop.org
Subject: [Bug 106228] amdgpu reads back brightness 0 (which is not true) if checked before a brightness has been explicitly set
Date: Wed, 25 Apr 2018 03:43:32 +0000	[thread overview]
Message-ID: <bug-106228-502@http.bugs.freedesktop.org/> (raw)

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https://bugs.freedesktop.org/show_bug.cgi?id=106228

            Bug ID: 106228
           Summary: amdgpu reads back brightness 0 (which is not true) if
                    checked before a brightness has been explicitly set
           Product: DRI
           Version: unspecified
          Hardware: Other
                OS: Linux (All)
            Status: NEW
          Severity: normal
          Priority: medium
         Component: DRM/AMDgpu
          Assignee: dri-devel@lists.freedesktop.org
          Reporter: jian-hong@endlessm.com

Created attachment 139091
  --> https://bugs.freedesktop.org/attachment.cgi?id=139091&action=edit
The full dmesg

I have tried to install Linux OS on ASUS laptop which is equipped with AMD
Ryzen 5 2500U with Radeon Vega Mobile Gfx.

When the Linux installation completed and entered to the OS, the brightness of
display looks normal but the brightness bar is shown as the lowest level within
the display's brightness GUI setting.

Also check "cat /sys/class/backlight/amdgpu_bl0/brightness" and it is 0.

After a system reboot, Brightness is dimmed to the lowest level.
Check "cat /sys/class/backlight/amdgpu_bl0/brightness" again and it is 12.

To make sure it is the problem that "system always reads back brightness 0 if
checked before a brightness has been explicitly set".
I disable all of the brightness setting applications, including masking
systemd-backlight service and than reboot.
"cat /sys/class/backlight/amdgpu_bl0/brightness" before set brightness manually
again and it reads back 0, but the brightness of display looks normal actually.
Then, if I drag the brightness bar in GUI, the actual brightness changes and
the "/sys/class/backlight/amdgpu_bl0/brightness" goes to the right value.
And, I reboot again, then the same things happen again.

I also tried this with kernel v4.17.0-rc2.  It still has the same problem.

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