SPI-SLAVE driver for linux

Belows are in described in include/linux/spi/spi.h.

* A @spi_device is used to interchange data between an SPI slave
* (usually a discrete chip) and CPU memory.

Why are there no drivers for SPI-SLAVE?
Most of other serial drivers are provided and updated recently.
But SPI-SLAVE drivers are not included still now.

Originally Posted by win.tech2 Why are there no drivers for SPI-SLAVE?

From Linux Documentation/spi/spi-summary:

This document (and Linux) currently only supports the master side of SPI interactions.

IOW nobody has come up with an acceptable framework for SPI slaves that's similar to what's available for USB gadgets.
Also consider that the typical SPI slave is likely to use a microcontroller incapable of running Linux (although that could change in a few more years).

Regards

Originally Posted by win.tech2 But SPI-SLAVE drivers are not included still now.

On the Linux host side of the SPI bus, the device driver for the SPI Master controller is a platform driver that performs the actual I/O on the SPI bus.
There are no device drivers for the SPI slaves, but rather SPI protocol drivers.

There should be a protocol driver for each SPI slave on that bus.
The protocol driver prepares and receives the data for/from its SPI slave, and uses the kernel SPI framework to perform the I/O through the SPI master.
It is the protocol driver that interfaces with userspace, and handles the requests for the device node in /dev.

Source code for SPI protocol drivers are not located in drivers/spi, but rather located by the functionality of the slave device.
An SPI slave that performs A-to-D conversion is in drivers/iio/adc. An SPI slave that is an RS-232 communications link is in drivers/tty/serial. An SPI slave that is a realtime clock is in drivers/rtc.

A list of SPI protocol drivers in the Linux kernel can be generated by searching for a salient framework procedure such as spi_set_drvdata().

Regards