Mastering Embedded Linux Programming - Second Edition

Serial Peripheral Interface (SPI)

The SPI bus is similar to I²C, but is a lot faster, up to tens of MHz. The interface uses four wires with separate send and receive lines, which allow it to operate in full duplex. Each chip on the bus is selected with a dedicated chip select line. It is commonly used to connect to touchscreen sensors, display controllers, and serial NOR flash devices.

As with I²C, it is a master-slave protocol with most SoCs implementing one or more master host controllers. There is a generic SPI device driver, which you can enable through the kernel configuration CONFIG_SPI_SPIDEV. It creates a device node for each SPI controller, which allows you to access SPI chips from user space. The device nodes are named spidev[bus].[chip ...