AMD has accused several companies of infringing its patents. In particular, this refers to the sale of specific graphics related components. The US International Trade Commission has bolstered this claim by agreeing to investigate the matter.
LG, MediaTek, Vizio, and Sigma Design all face a cease and desist order should they be found in violation of US patent laws. However, the case is not exactly viewed as a move against the four companies in question. The claim is more of a proxy move against ARM which designs the GPUs in the first place.
Samsung, which also uses the same technology, is already licensing the patents from AMD. Which should help its case against the other four companies.
Moving against the manufacturers that actually produce the chips would be much easier than trying to build a case against ARM. Since there is a physical product to point to and profits are easier to establish. More importantly, it’s a shot across the bow against other who are looking to incorporate ARM based graphics into their mobile devices.