We have 2 separate sites for desktop (www.example.com) and mobile (m.example.com)

As per the guideline, we have added Rel=alternate tag on www.example.com to point to mobile URL(m.example.com) and Rel=canonical tag on m.example.com to point to Desktop site(www.example.com).However, i didn't find any guideline on what canonical tag we should add ifFor Desktop sitewww.example.com/PageA - has a canonical tag to www.example.com/PageBOn this page, we have a Rel=alternate tag m.example.com/pageAWhat will be the canonical we should add for the mobile version of Page Am.example.com/PageA - Canonical tag point to www.example.com/PageA -or www.example.com/PageB?Kalpesh