Why I can't control the brightness/backlight level?

At the first:

Notebook Positivo BGH - C500 Series. 

Processor: AMD C60 series (dual core 800 mhz-1ghz)

GPU: Radeon HD 6290 (worked with fglrx/Catalyst)

Hello everybody, this is my first post in 8-years-use of Ubuntu/Kubuntu, I've never had problems with any version, but when I've upgraded from Willy to Xenial I haven't take care in the latest version that the AMD/ATI property drivers (fglrx) have been discontinued or unsupported by the developers, and they advice against not upgrade for AMD users. The Fn keys dosen't work!

However, after upgrade, when I was configuring, I want install drivers from console:

sudo apt-get install fglrx fglrx-updates 

"fglrx" and "fglrx-updates" has no candidates

In the version Willy (and previous versions), I can't control or lower the brightness/backlight util the property drivers have been instaled.

In Ubuntu 16.04, the drivers are:

xserver-xorg-video-amdgpu

xserver-xorg-video-radeon

And These are open drivers, but this is not the trouble really.

I've tried the following procedures:

I tried to put various links, but the newbies can't post more 2 links

Abstract:

1. Can't change backlight level by installing driver.

    sudo apt-get install xserver-org-video-amdgpu

    sudo apt-get install xserver-org-video-radeon

##2. It persist high shine, despite modifing /sys/class/backlight, and the promp shows me (radeon_bl0 is present):

    lspci | grep ati

    00:01.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] Wrestler [Radeon HD 6290]

    ls /sys/class/backlight

    radeon_bl0

Inside the folder, brightness, max_brightness, actual_brightness, bl_power and others are present

    echo > 10 /sys/class/backlight/radeon_bl0/brightness 

There is no effect

    echo > 100 /sys/class/backlight/radeon_bl0/max_brightness

    permission denied

    chmod 0777 /sys/class/backlight/radeon_bl0/max_brightness

    nano /sys/class/backlight/radeon_bl0/max_brighness

    modifing 255 to 100

    Ctrl+O > I/O Error 

    chmod 0777 /sys/class/backlight

    The same result >  I/O Error 

And find another way:

    ls -alh /sys/class/backlight

    lrwxrwxrwx  1 root root 0 abr 23 12:23 radeon_bl0 -> ../../devices/pci0000:00/0000:00:01.0/drm/card0/card0-LVDS-1/radeon_bl0

And trying the same, and no effect.

3. Modifing the grub:

    GRUB_CMDLINE_LINUX="acpi_osi=Linux" | No effect

    GRUB_CMDLINE_LINUX="acpi_backlight=none" | No effect

    GRUB_CMDLINE_LINUX="acpi_backlight=vendor" | No effect

    GRUB_CMDLINE_LINUX="acpi_backlight=video" | No effect

    GRUB_CMDLINE_LINUX="acpi_backlight0" | No effect

    GRUB_CMDLINE_LINUX="acpi_backlight=radeon_bl0" | No effect

Rebooting and edit grub (with the same sentences) before start Ubuntu, strangely It don't start.
Starting in "recovery mode", /sys/class/backlight, shows me:

     acpi_video0

But the SDDM dosen't start.

4. Adding the X11 configuration.

      cd /usr/share/X11/xorg.conf.d

      dir > 10-amdgpu.conf is present

      nano 10-amdgpu.conf | shows me



               Section "OutputClass"

                 Identifier "AMDgpu"

                 MatchDriver "amdgpu"

                 Driver "amdgpu"

               EndSection

I added



              Section "Device"

                Identifier "card0" | put also "AMDgpu"

                Driver "amdgpu" 

                Option "Backlight" "radeon_bl0"

                BusID "PCI:00:01:01"

             End Section

But it dosen't work, due option "Backlight" is for intel driver. I revised man of amdgpu and not figure this option. In several times, neither starts SDDM.

5. Using the command setpci:

     setpci -s 00:01.0 F4.B=7F | Not work

     setpci -s 00:01.0 F4.B=FF | Not work

     setpci -s 00:01.0 F4.B=50 | Not work

     setpci -s 00:01.0 F4.B=80 | Not work

This video card not support by the setpci

6. Installing xbacklight

     sudo apt-get install xbacklight

     xbacklight -s 80 | there is no effect 

     No outputs have backlight property 

     xbacklight -d LVDS -s 80

     RANDR Query Version returned error -1

It dosen't work, I've searched, and xbacklight is deprecated for xf86-video-ati for control of backlight, I've installed script "light" (lightscript) but It dosen't work too.

7. Making udev rule:

          nano /etc/udev/rules.d/81-backlight.rules



          # Set backlight level to 8

         SUBSYSTEM=="backlight", ACTION=="add", KERNEL=="acpi_video0", ATTR{brightness}="8"

          Save & Exit and there is no effect after boot

8. Using systemd-backlight service.

           I don't understeand how this works, but I've got this from the prompt: 

           systemctl list-units | grep -i backl



           systemd-backlight@backlight:radeon_bl0.service     loaded active exited    Load/Save Screen Backlight Brightness of backlight:radeon_bl0



           system-systemdx2dbacklight.slice       loaded active active    system-systemdx2dbacklight.slice

The systemd-backlight service is loaded for /sys/class/backlight ! But It dosen't work, the backlight don't change.

9. Using xrandr

       Finally I put in the console:

xrandr --output LVDS-1 --brightness 0.6 | 0.4 | 0.3

Previously identified output 

This "worked" for me, but when I restart the values of xrandr going to default, by more than I put xrandr --output LVDS1 --brightness 0.5 at start session. (On Kde by the System Settings>Start and Shutdown)

Conclussion

In all cases, the brightness/backlight ever is high, it dosen't matter I do, the Fn Keys don't work, and the Kde Indicator for brightness goes to 0 and the LCD looks the Christmas tree because it's turn up/down infinitely.

Anyone have more ideas?

Sorry for my bad english!

There's something very odd about the syntax you're using to write to the files in /sys/class/backlight/. Please try this, instead:

echo 128 | sudo tee /sys/class/backlight/radeon_bl0/brightness

By the way, you were not able to modify "max_brightness" because that file is just there to let you know the maximum brightness you can use. You need to change the file named "brightness".

About your shell syntax: The shell redirection operator > only works if you're already running a shell as root (for example, using sudo -s), but I should let you know that doing so is generally considered a bad idea. Logging in to a root shell gives you great power; and with great power comes great whopping mistakes. It's easy to forget you're running as root and then accidentally mess up your whole system. That's why I recommend sudo, as in the example above. Sudo is a reminder to be careful: anything after the word sudo is normally off-limits and potentially dangerous.

However, if you are curious, it is possible to use the > file
redirection operator the way you were asking, but you'd need to change
the arguments around. The part that comes after the > is the
filename to write to, the part before it is the command whose output
you want to redirect. So, for example,

$ sudo -s

# cd /sys/class/backlight/*/

# echo 128

128

# echo 100 > brightness

# cat brightness

100

# echo 200 > brightness

# cat max_brightness

255

# cat max_brightness > brightness

# cat brightness

255

# exit

$ 

(You'll notice your prompt changes to a hash mark when you're running a
root shell. That's a subtle warning sign. Typing exit will get you
back to the safety of your normal user account.)

there is no standard brightness level resolution in universal implementation. For example one of my linux boxes is a Toshiba Satellite L510 and has an 8 bit resolution. i.e. my /sys/class/backlight/acpi_video0/brightnesswill only accept values in [0,7]. I also have seen one other system has a resolution of 23 bits. i.e. [0-22].

To know the range of brightness values, read your /sys/class/backlight/radeon_bl0/max_brightness file. Also the value of the max_brightness file is most likely set by your system's firmware and you can not write to it. But the /sys/class/backlight/radeon_bl0/brightness file can be written to as long as the value being written is between 0 and the result of

cat /sys/class/backlight/radeon_bl0/max_brightness

also suspending your system and waking it up usually fixes some problems with regard to ACPI and UEFI - by extension functions keys. to suspend your system use the following command.

sudo pm-suspend

then wake your system by pressing the power button and check is the function keys are working.