The is primarily a communication interface for JieLi (JL) Bluetooth chips , which are common in low-cost audio devices like Bluetooth speakers and headphones. The "SPP" refers to the Serial Port Profile , which allows these chips to emulate a virtual serial port for data transfer and device management. Key Functionality
A common pitfall: forgetting to call dma_sync_single_for_device() before enqueuing a TX buffer, leading to stale data. jl-spp driver