When the whole mobile device took off Google came out and stated using a directory /m or a subdomain m.abc.com was perfectly acceptable, They understood either routes and many went the subdomain route.
However, things have moved on and now googles primary search results is the mobile version of the site. With this in mind, most webmasters dropped their m.abc.com version and went for a responsive design.
Having a responsive design means you only have 1 lot of code to look after so long term makes your life a hell of a lot easier.
Having said that if making it a responsive site and you're now stuck with 2 separate sites then both canonicals (desktop and mobile) should point to the mobile version as this is what Google will be indexing and largely ignoring your desktop version.