[Bug 90151] New: Laptop Backlight Issue with Hybrid Graphics System

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=90151

            Bug ID: 90151
           Summary: Laptop Backlight Issue with Hybrid Graphics System
           Product: xorg
           Version: unspecified
          Hardware: x86-64 (AMD64)
                OS: Linux (All)
            Status: NEW
          Severity: normal
          Priority: medium
         Component: Driver/Radeon
          Assignee: xorg-driver-ati at lists.x.org
          Reporter: k.sarendranath at gmail.com
        QA Contact: xorg-team at lists.x.org

Kernel Version: 3.19.3
Radeon Version: 1:7.5.0-2
Xorg Verison: 1.17.1-5


The system being used is a Lenovo Thinkpad configured with an R7 M260DX
discrete card attached to an A10-7300. Upon booting it, the kernel spits out
this message:


[drm:radeon_acpi_init [radeon]] *ERROR* Cannot find a backlight controller


with the quirk of having the brightness hotkeys not being able to control the
brightness. Looking into the radeon source, here is where the call came from
(radeon_acpi.c):


atif->encoder_for_bl = target;
        if (!target) {
            /* Brightness change notification is enabled, but we
             * didn't find a backlight controller, this should
             * never happen.
             */
            DRM_ERROR("Cannot find a backlight controller\n");
        }

Is this an issue within the driver or from Lenovo's acpi implementation?

If anything, I can control the backlight by using the /sys/ subsystem so I can
remap the hotkeys to control the brightness while systemd will store it on
reboot. In essence, I just wanted to bring this to attention due to the comment
in the source.

Also a quick question on hybrid graphics, the radeon feature matrix states that
Enduro is mostly complete and I believe that this lenovo system is muxless.
Checking vgaswitcheroo, the integrated card is used while the discrete card is
"DynOff" which I presume is dynamically off. Does that mean the driver is
currently powering on the discrete card when rendering is required? Or is
something else required?

Thanks for any answers.

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