yum list all available packages in a repo

To list all packages available on a specific repo, run

yum  --disablerepo="*" --enablerepo="REPO_NAME_HERE" list available

You can get list of all available repos with command

yum repolist

Example: 

yum  --disablerepo="*" --enablerepo="litespeed" list available

This command list all packages available in repo "litespeed"