How to determine primary GPU?

[Ashark]

Hello. Here I saw a log of gpu manager, and I am interested how it works. I am looking answer for the question https://stackoverflow.com/questions/19985131/how-identify-the-primary-video-card-on-linux-programmatically
This is needed for my project in which I detect many info about gpu on the user's system.
If user has multiple GPUs, I need to understand which is primary, because I need to do different things for different GPUs.

I am especially interested in theese parts of the log:

Vendor/Device Id: 8086:1902
BusID "PCI:0@0:2:0"
Is boot vga? no  # <-- How ?
Vendor/Device Id: 10de:1c81
BusID "PCI:1@0:0:0"
Is boot vga? yes  # <-- How ?
Does it require offloading? yes # <-- How?

I would be glad if you point me in the right direction. How do I identify the gpu that is used as main/primary/boot?
Is it possible with drm_info? I tried to manually make another card as a primary at boot, and the order of gpus list in drm_info did not changed. I need some way to say if particular gpu is currently primary.