It is possible to use 2560x1080 resolution on Linux using ATI Radeon?

What do you need? Whats missing?

Dont do that. Besides this being a generally bad idea for handling any software in linux (we use repositories and packages and such … and they usually are tied to things like system libraries)… manjaro also has MSM/mhwd to handle these things. Dont deviate from that unless you have a good reason and know what you are doing.

Please see this: