Bug 108668

Summary:	drm/amd/display: set backlight level limit to 1: breaks userspace programs assuming 0 is the minimum brightness
Product:	DRI	Reporter:	Samantha McVey <samantham>
Component:	DRM/AMDgpu	Assignee:	Default DRI bug account <dri-devel>
Status:	RESOLVED FIXED	QA Contact:
Severity:	normal
Priority:	medium
Version:	unspecified
Hardware:	Other
OS:	All
Whiteboard:
i915 platform:		i915 features:

Description Samantha McVey 2018-11-05 20:27:57 UTC

This commit https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=0cafc82fae41531b0162150f9a97f2c74f97118f breaks KDE and any other software that assumes setting 0 will induce the minimum brightness. Maybe it would make more sense to set the brightness level to "1" if userspace requests brightness level "0" so programs still function correctly.

If desired the call could still return false to indicate it was out of bounds, but still lower brightness.

Comment 1 Samantha McVey 2018-11-05 20:41:35 UTC

In addition, even though there is a write error, when you read back the brightness value, it shows that the backlight is at level 0, while its brightness has actually been unchanged from before:

echo 0 > /sys/devices/pci0000:00/0000:00:08.1/0000:05:00.0/backlight/amdgpu_bl0/brightness
bash: echo: write error: Invalid argument

cat /sys/devices/pci0000:00/0000:00:08.1/0000:05:00.0/backlight/amdgpu_bl0/brightness
0

Comment 2 Harry Wentland 2018-11-06 16:59:58 UTC

This should fix it: https://patchwork.freedesktop.org/patch/260537/

Comment 3 Samantha McVey 2018-11-30 03:20:57 UTC

Closing this since it has been fixed.

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