Linux and Radeon hd2400 backlight, how to make them friends?

Question

linux

I decided to install linux for home use, the choice fell on debian 8 with xfce, everything started up and works fine, but I ran into one problem, I dug this way and that, but I could not overcome it, I hope for your help, friends.
I have an asus m51sr laptop with a radeon hd2400 graphics card.
The Fn keys on it adequately adjust the backlight of the screen in the state when no axis is loaded, visually the brightness ranges from 20% to 100%.
Also they adequately work from under wines (xp/win7/win10).
But when running on a debian (and ubuntu) laptop, these keys adjust the backlight between 0%-80% visibility, with flickering at medium values.
Adjustment via the module on the panel gives exactly the same result.
Writing values ​​to the /sys/class/backlight/acpi_video0 (/radeon_bl0)/brightness files also change the backlight skewedly.
Changing the boot option acpi_backlight=native (video/vendor/none) has no effect.
It is noteworthy that if you boot from a clean debian without installing a driver, then the backlight works as it should from both the keys and the panel, but the image is out of the blue and does not in any way work.
Please tell me how you can overcome the driver, or in extreme cases, turn off the backlight control using the driver, so that you get the option as with a clean installation, but with video card support.
Now on Debian 8.5 (jessie) laptop, kernel 3.16.0-4-686-pae
Packages: firmware-linux-nonfree, xserver-xorg-video-radeon, xserver-xorg-video-ati

Answer 1

Problem solved.
#dmesg, looking for a highlight message, in my case this is:
Download the required "linux-source" and find the file with this phrase.
In this file, at the beginning of the backlight initialization function, we write "return;"
We assemble the core, the crutch is ready.
As a result: full screen brightness at maximum, adequate operation of fn keys and modules that change brightness, no flickering and whistling of the inverter.