https://bugzilla.kernel.org/show_bug.cgi?id=70571
Bug ID: 70571
Summary: acpi-video-backlight code should filter duplicate
entries from brigthness values table (BCL)
Product: ACPI
Version: 2.5
Kernel Version: 3.13
Hardware: All
OS: Linux
Tree: Mainline
Status: NEW
Severity: normal
Priority: P1
Component: Power-Video
Assignee: [email protected]
Reporter: [email protected]
Regression: No
Created attachment 126081
--> https://bugzilla.kernel.org/attachment.cgi?id=126081&action=edit
acpidump of Dell Latitude E6430 with the latest A14 BIOS
See:
http://www.spinics.net/lists/linux-acpi/msg48954.html
For a patch fixing this, here is the commit msg explaining the issue:
Some devices have duplicate entries in there brightness levels table, ie
on my Dell Latitude E6430 the table looks like this:
[ 3.686060] acpi backlight index 0, val 80
[ 3.686095] acpi backlight index 1, val 50
[ 3.686122] acpi backlight index 2, val 5
[ 3.686147] acpi backlight index 3, val 5
[ 3.686172] acpi backlight index 4, val 5
[ 3.686197] acpi backlight index 5, val 5
[ 3.686223] acpi backlight index 6, val 5
[ 3.686248] acpi backlight index 7, val 5
[ 3.686273] acpi backlight index 8, val 6
[ 3.686332] acpi backlight index 9, val 7
[ 3.686356] acpi backlight index 10, val 8
[ 3.686380] acpi backlight index 11, val 9
etc.
Notice that brightness values 0-5 are all mapped to 5. This means that
if userspace writes any value between 0 and 5 to the brightness sysfs attribute
and then reads it, it will always return 0, which is somewhat unexpected.
This is a problem for ie gnome-settings-daemon, which uses read-modify-write
logic when the users presses the brightness up or down keys. This is done
this way to take brightness changes from other sources into account.
On this specific laptop what happens once the brightness has been set to 0,
is that gsd reads 0, adds 5, writes 5, and on the next brightness up key press
again reads 0, so things get stuck at the lowest brightness setting.
Filtering out the duplicate table entries, makes any write to brightness
read back as the written value as one would expect, fixing this.
I've attached an acpidump of the laptop in question.
--
You are receiving this mail because:
You are watching the assignee of the bug.
------------------------------------------------------------------------------
Android apps run on BlackBerry 10
Introducing the new BlackBerry 10.2.1 Runtime for Android apps.
Now with support for Jelly Bean, Bluetooth, Mapview and more.
Get your Android app in front of a whole new audience. Start now.
http://pubads.g.doubleclick.net/gampad/clk?id=124407151&iu=/4140/ostg.clktrk
_______________________________________________
acpi-bugzilla mailing list
[email protected]
https://lists.sourceforge.net/lists/listinfo/acpi-bugzilla
