What was the relationship between the Shona people and the groups along the Swahili Coast?

Shona people has the largest population of indigenous people in zimbabwe that is composed of more than 9 million people. They have products such textiles, golds, and copper. Swahili groups situated near Swahili coast shows interest with the Shona's people goods that is why the Swahili people chose to trade with Shona people.