Patent infringement refers to the unauthorized use of patented technology. The criterion is whether the technology covered by the patent claim of the other party is used.
Attention is the content of the claim, and what is not required in the claim is not infringement.
Your situation here depends on the protection scope of patent A and patent B. B can apply for more functions than A as the protection scope of B, but if all the contents of B use the technology within the protection scope of A, it will infringe A. ..
In this case, there may be mutual infringement (for example, if A wants to use new functions, it may infringe on B). Therefore, many large companies will have patent cross-licensing agreements.