It's a well-known fact that AMD’s support for their GPUs is rather poor on the Linux platform, even if some AMD owners don't really want to accept it. The best proof of this situation is the fact that Valve developers are now tracking the new AMD releases in order to compile the issues that are found by the community.

NVIDIA, AMD, and Intel have pretty much all of the market share on GPUs on the Linux platform. Intel doesn't really compete with the other two companies in terms of performance, so they are not really important in this matter, although their support is very good.

On the other hand, NVIDIA has really good proprietary drivers for their products, but AMD's are just adequate, for lack of a more insulting word. It's not just a problem of performance when it comes with AMD's drivers. The releases don't fix or bring any major improvements, they don't provide support for the latest Xorg or Linux kernel, and they often don't provide any kind of info about a released driver, just a simple download link.

Why is Valve tracking AMD’s problems?

Valve is looking to provide the best performance for their SteamOS Linux distribution and the company needs to be sure that users have the best possible experience. AMD has the second most used GPUs among Steam users, and it stands to reason that the proportion will remain the same when SteamOS finally starts to ship with the Steam Machines (PC / console hybrid).

The main problem is that the AMD drivers are not reliable. In fact, some future games won't work with AMD hardware or they will need a lot of attention. This is an unacceptable situation and Valve is trying to fix this problem. They've set up a forum topic that is updated with problems found in the AMD drivers.

This is the list so far: black or flickering screen when fullscreen mode is enabled in certain games, lower performance and hitching in games compared to desktop distributions, crackling sound over HDMI, graphics memory reported as -0GB in System information; this is a Steam bug with reporting memory amount and doesn't affect actual usage of the graphics memory.

The fact that Valve, not AMD, has to do this is not really flattering for the hardware company. You won't find this kind of topic with NVIDIA or Intel hardware, which points towards a problem with AMD.