You should be fine then, unless some other part of Linux is using it as I/O. That is unlikely. Your driver will need to configure the pins to connect them to the SPI peripheral internally. You'll need to look at the chip's user manual for details on how to do that.SPI is neither a char or a block device because those are abstract Linux terms used to classify a device. However, your driver should probably present SPI as a char device.What exactly are you trying to achieve with SPI? It sends and receives synchronously, so a slave cannot simply send data, and similar a master cannot simply receive data. It doesn't work like a normal UART-like device.