This is related to the OS detection in _BCM control method in DSDT;
however, this is a system from 2012 and it is not likely have any BIOS
update from this.
There are two possible solutions -
1. add a quirk in drivers/acpi/blacklist.c such as below:
+ {
+ .callback = dmi_disable_osi_win8,
+ .ident = "HP Pavilion dv6",
+ .matches = {
+ DMI_MATCH(DMI_SYS_VENDOR, "Hewlett-Packard"),
+ DMI_MATCH(DMI_PRODUCT_NAME, "HP Pavilion dv6 Notebook PC"),
+ },
+ },
This is tested and it works well.
2. newer version of linux kernel enable "use_native_backlight" by
default. This remove ACPI video brightness out of picture and therefore
_BCM will not be used.
This is tested with mainline kernel @ http://kernel.ubuntu.com/~kernel-
ppa/mainline/v3.19-vivid/
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https://bugs.launchpad.net/bugs/1416940
Title:
[HP Pavilion dv6] Brightness control only work on the last two steps
on 12.04.5
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