I tried everything that is in this thread.
The brightness increase / decrease buttons do not work. Debian 8, Lenozo Z500
if I set GRUB_CMDLINE_LINUX_DEFAULT = "quiet acpi_backlight = vendor" in grub, then the fn + buttons add and subtract decrease the brightness, but the maximum screen brightness is lower than it should be.
if you add acpi_osi = Linux there, then everything is fine and bright with brightness, but then the nvidia video card disappears from the system at all (it is not displayed in lspci).
00: 02.0 VGA compatible controller: Intel Corporation 3rd Gen Core processor Graphics Controller (rev 09)
01: 00.0 3D controller: NVIDIA Corporation GK208M [GeForce GT 740M] (rev a1)
I tried it all on kali linux rolling on gnome3 with proprietary nvidia drivers now debian 9 on kde, it's all the same, so I don’t think this is important.
acpi_backlight = vendor is also needed for bbswitch
It would be ideal if there is a file in which you can increase the maximum brightness value or maybe a command.
as far as I understood it is necessary to create a config for xorg, and use it in grub, but since a newbie to linux doesn't know what and how, or why. More interesting is the "vendor" from where is it, what is it and where can I see the settings for this. As well as acpi_osi = Linux. :)
Sorry if that is not according to the rules issued. Thank you in advance.
when I set up acpi_osi = Linux in grub, then intel_backlight is used (in sys / class / backlight / intel_backlight) I am maximizing, not regulated and nvidia disappears
if acpi_backlight = vendor then ideapad is used (sys / class / backlight / ideapad) is regulated, there is nvidia, but when using then brightness is lower than it should be (maximum is darker than it should be)
I am even ready to sacrifice the adjustment if only I was to the maximum and nvidia did not fall away
