Mdthbs

I've just installed a fresh new Debian 9 LXDE into an ACER AMD Notebook and everything seems to be working fine. However, during the boot, there is an annoying Strong Backlight Flash (seems like a photo flash). The sequence of events are basically as following:

• Boot starts at maximum backlight brightness


• Debian OS is selected at GRUB menu


• Some messages appear in low resolution at the command line


• Strong Backlight Flash


• Command line is now in high resolution


• Backlight Brightness is set to user pre-defined level


• LXDE login screen

Considering that during the Windows era of this notebook such flash never happened, I'm pretty sure there is a way via software to avoid that.

Question

How to avoid this Strong Backlight Flash?

Debug

root@debian:~# dmesg | grep -i "error|firmware|backlight"

[    0.000000] Command line: BOOT_IMAGE=/boot/vmlinuz-4.9.0-6-amd64 root=UUID=740fe980-f018-4c49-b139-613d41d30fb9 ro quiet acpi_backlight=video

[    0.000000] Kernel command line: BOOT_IMAGE=/boot/vmlinuz-4.9.0-6-amd64 root=UUID=740fe980-f018-4c49-b139-613d41d30fb9 ro quiet acpi_backlight=video

[    0.294171] ACPI: [Firmware Bug]: BIOS _OSI(Linux) query ignored

[    0.311772] acpi PNP0A08:00: [Firmware Info]: MMCONFIG for domain 0000 [bus 00-3f] only partially covers this bridge

[    1.057843] pci 0000:01:00.0: [Firmware Bug]: disabling VPD access (can't determine size of non-standard VPD format)

[    7.131791] EXT4-fs (sda1): re-mounted. Opts: errors=remount-ro

[   12.551069] radeon 0000:00:01.0: firmware: direct-loading firmware radeon/PALM_pfp.bin

[   12.685950] radeon 0000:00:01.0: firmware: direct-loading firmware radeon/PALM_me.bin

[   12.705633] radeon 0000:00:01.0: firmware: direct-loading firmware radeon/SUMO_rlc.bin

[   12.762705] radeon 0000:00:01.0: firmware: direct-loading firmware radeon/SUMO_uvd.bin

[   13.481390] [drm] radeon atom DIG backlight initialized  

Hardware Specifications
Notebook Aspire E1-421-0622 | product details

• AMD 2 Core™ Processor E1-1200 (1.4 GHz) 1MB Cache 64-bit Processing


• AMD Radeon HD 7310 Graphics Controller


• 2Gb DDR3 SDRAM Memory


• 256MB shared video memory

Debian Strech
debian-9.4.0-amd64-netinst.iso

• Software selection
  
  (  ) Debian desktop environment
  
  (  ) ... GNOME
  
  (  ) ... Xfce
  
  (  ) ... KDE
  
  (  ) ... Cinnamon
  
  (  ) ... MATE
  
  (X) ... LXDE
  
  (  ) web server
  
  (X) print server
  
  (  ) SSH server
  
  (X) standard system utilities


• 
  

  Minor adjustments:

  
  
  
  
  
  • Non-free package firmware-amd-graphics installed (full discussion)
  
  
  • 
    

    /etc/default/grub file updated (full discussion):

    
    
    

    GRUB_CMDLINE_LINUX_DEFAULT="quiet acpi_backlight=video"  
    
    

    
    
  
  
  
  

I felt unhappy about the same problem on my laptop maybe longer then this question stays open.

There is a solution:
Disable backlight control in radeon driver by adding radeon.backlight=0 to kernel boot parameters.

But.
The problem here is that you might need another module to control the backlight. This means that instead of acpi_backlight=video you first should test your system with acpi_backlight=vendor or acpi_backlight=native.

More about backlight on Arch Wiki and about ACPI video extensions in kernel docs.