The driver architecture

The required header for SPI stuff in the Linux kernel is <linux/spi/spi.h>. Before talking about the driver structure, let's see how SPI devices are defined in the kernel. An SPI device is represented in the kernel as an instance of spi_device. The instance of the driver that manages them is the struct spi_driver structure.

The device structure

The struct spi_device structure represents an SPI device, and is defined in include/linux/spi/spi.h:

struct spi_device { 
    struct devicedev; 
    struct spi_master*master; 
    u32 max_speed_hz; 
    u8 chip_select; 
    u8 bits_per_word; 
    u16 mode; 
    int irq; 
    [...] 
    int cs_gpio;        /* chip select gpio */ 
}; 

Some fields that are not meaningful for us have been removed.  The following are the meanings of the elements in the structure:

• master: This represents the SPI controller (bus) on which the device is connected.
• max_speed_hz: This is the maximum clock rate to be used with this chip (on the current...