<html> <head> <base href="https://bugs.freedesktop.org/" /> </head> <body> <div> <a class="bz_bug_link bz_status_NEEDINFO " title="NEEDINFO --- - [gm45] Backlight shuts off during boot when KMS is enabled" href="https://bugs.freedesktop.org/show_bug.cgi?id=53153#c34">Comment # 34</a> on <a class="bz_bug_link bz_status_NEEDINFO " title="NEEDINFO --- - [gm45] Backlight shuts off during boot when KMS is enabled" href="https://bugs.freedesktop.org/show_bug.cgi?id=53153">bug 53153</a> from <a class="email" href="mailto:jpabbott02@gmail.com" title="Jay Abbott <jpabbott02@gmail.com>"> Jay Abbott</a> <pre>Trying to change the brightness with the wmi hotkeys DOES send a value to '/sys/class/backlight/acpi_video0', but the screen does not change. Each time I press Fn+[RightArrow] the value will change in this sequence: [0,2,4,6,8,9]. I'm stating the obvious here, but to consolidate what we know up to this point: The ACPI backlight control does not work, so we're forced to use the drm to adjust it instead. The drm backlight control is buggy - the max brightness is the minimum and vice versa. So when the drm kicks in during boot and tries to set the brightness to max, the backlight shuts off. The parameter i915.invert_brightness=1 solves this problem. So the issue here is really twofold. There is a buggy ACPI which fails to set the brightness, and a buggy drm which sees brightness values as their inverse. Now here's the game-changer: I was looking at dmesg and I noticed it always returns this line: [ 11.089157] acer_wmi: Brightness must be controlled by acpi video driver I realized that the above line must be critical in understanding what is wrong with the brightness controller, but I wasn't sure how to interpret it. So I did some research on the acer_wmi module, and it turns out I need to enable the backlight subsystem in my kernel config. Take a look, there needs to be an additional controller called "backlight" here: jay@jay-debian:/sys/devices/platform/acer-wmi$ ls driver interface modalias power rfkill subsystem uevent I will recompile with this enabled and let you know how it goes. With this finally out of the way, we can focus on figuring out why the drm brightness control is working backwards.</pre> </div> <hr> You are receiving this mail because: <ul> <li>You are the QA Contact for the bug.</li> </ul> </body> </html>