ASUS 401A has some fundamental problems with its BIOS ASL code.
First, its _BCL returns
[ 344.088661] Brightness[0] = 100
[ 344.088669] Brightness[1] = 77
[ 344.088672] Brightness[2] = 60
[ 344.088675] Brightness[3] = 48
[ 344.088677] Brightness[4] = 43
[ 344.088680] Brightness[5] = 38
[ 344.088682] Brightness[6] = 33
[ 344.088684] Brightness[7] = 28
[ 344.088687] Brightness[8] = 23
[ 344.088689] Brightness[9] = 18
[ 344.088692] Brightness[10] = 10
However, _BCL should returns elements like (from B.6.2 of ACPI spec
4.0a)
Method (_BCL, 0) {
// List of supported brightness levels
Return (Package(7){
80, // level when machine has full power
50,// level when machine is on batteries
// other supported levels:
20, 40, 60, 80, 100}
}
Secondly, its _BQC returns the nth level of brightness, but ACPI spec
requires "An Integer containing the current brightness level (must be
one of the values returned from the _BCLmethod). For example, when the
brightness is "10", _BQC returns 0. When the brightness is "18", it
returns 1. This causes a lot of confusion to kernel who does not how to
control brightness. Last, _BQC always returns 0 on boot time.
However, I don't think ASUS is going to release BIOS fixes for it.
Fortunately, the brightness is not too dim to be visible (not completely
dark).
** Changed in: linux (Ubuntu)
Status: Confirmed => Incomplete
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https://bugs.launchpad.net/bugs/1132649
Title:
display brightness is very low by default
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