Our suggestion would be to take the ALSA bus towards Grandas de Salime from Oviedo to Tineo - there might be only 1 bus per day. More buses go to Salas, but that is an extra day's walking. If Tineo is too many days then going to Pola de Allande, Berducedo or Grandas itself is an option. Starting in Pola de Allande gives you the walk over the beautiful mountain pass at Puerto de Palo. There is
no public transport beteween Grandas and Fonsagrada, but you can shorten the long day after Fonsagrada by taking the little bus to Cádabo from there or from Paradavella (Lugo bus - 3 a day?). If short of time I would choose to start in Tineo or Pola and then shorten a day, or miss a stage, elsewhere because the Camino between there and Fonsagrada is what makes the Primitivo so special. If you have the
CSJ guide to the Primitivo (Caminos del Norte; F) then you can work out the distances and it will help choose your starting point. Distances are also on our Primitivo blog, see link below my post, we walked short days so took 'double time'.
Note: You reach Grandas by bus from the Oviedo side only and Fonsagrada by bus from the Santiago/Lugo side only.
Buen Camino