What's the difference between Xiaomi of Xiaomi Company and Redmi's foundry?

Xiaomi's two mobile phone brands, of which Xiaomi brand is independently designed and manufactured by Foxconn and Inventec, and now BYD has been added; The mobile phones under Redmi brand are all bought from ODM, and Xiaomi changed them by himself (now Redmi is independent, and Redmi company changed them). After optimizing the scheme, they were commissioned for production, mainly in Wen Tai and Qi Long.