Fix Radeon HD 6400 Series (Caicos) on Ubuntu

Hi, I got my old VGA card black/blank display when using Ubuntu 24.04. On Windows 10 it is work perfectly on 1440p (2K) resolution.

Here is my VGA card info:

$ lspci -k -d ::03xx                                                                                                                                      
01:00.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] Caicos [Radeon HD 6450/7450/8450 / R5 230 OEM]                                  │
        Subsystem: Bitland(ShenZhen) Information Technology Co., Ltd. Radeon HD 6450                                                                      
        Kernel driver in use: radeon                                                                                                                      
        Kernel modules: radeon, amdgpu 

This old card correctly use radeon driver instead of newer amdgpu driver. I also can confirm driver is works well by executing DRI_PRIME=1 glxgears while monitoring Radeon GPU usage with radeontop utility.

But still monitor will be blank if change from onboard Intel GPU (i915) to Radeon GPU on PCIe interface. 😭

After days of googling, go to forums, try and error. ChatGPT is life saver 😃

Here options need to grub config /etc/default/grub to fix those issue:

#GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"
GRUB_CMDLINE_LINUX_DEFAULT="radeon.si_support=1 radeon.cik_support=1 amdgpu.si_support=0 amdgpu.cik_support=0 radeon.dpm=0 radeon.audio=0 radeon.modeset=1"

Then sudo update-grub

It now my monitor can display 2560x1440p (2K) again. yay...🎉