The present invention provides a compound of formula I; or a pharmaceutically acceptable salt thereof, wherein R 1 , R 2 , R 3 , R 4 , R 6 , A 1 , A 2 , X 1 , sand m are defined herein. The invention also relates to a method for manufacturing the compounds of the invention, and its therapeutic uses. The present invention further provides a combination of pharmacologically active agents and a pharmaceutical composition.