How can i find some special code in linux kernel ?

furukawabakery

due to my low english proficiency,please don’t be surprised if there are any strange expressions.

I'm trying to develop a driver for a device like this to solve some of the device's problems.

In the above link, there is a column named ‘CrossDisplay Switching’, which describes in detail the issues related to this device and the solutions provided by their company. However, this only works on Windows systems, and this problem still exists and has not been resolved in early versions of Linux (the specific kernel version may be 3.X).
Then I tested the updated version of Linux (kernel version 6.X, system is Ubuntu) and found that this problem has been solved in the updated version of Linux. Now, for some reason, I need to solve this problem in early versions of Linux as well, and the solution seems to be hidden in the code of the new version of Linux.
In summary, my question is: How can I find a solution to this problem in the vast amount of code in Linux? Or if someone knows how to solve this problem in early versions of Linux, please kindly advise. Thank you very much!

This is a more detailed description of the problem and solution. Due to my limited English proficiency, I am borrowing this link to explain the issue.