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I am interested in working on SPI devices available in linux. I have a specific controller which supports SPI in both master and slave mode. I have to configure the SPI controller in slave mode.

My question: Does the Linux frame work support SPI slaves? I will get asynchronous data on SPI bus, I have to read this data and process it, then send back a command.

artless noise
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user3012531
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3 Answers3

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Support of SPI Slave Mode has been in the Linux kernel from revision v4.13-rc1. From SPI Documentation of Linux Kernel:

This document (and Linux) supports both the master and slave sides of SPI interactions.

[...]

A "struct spi_device" encapsulates the controller-side interface between those two types of drivers.

[...]

/sys/devices/.../CTLR/slave ... virtual file for (un)registering the slave device for an SPI slave controller.

Writing the driver name of an SPI slave handler to this file registers the slave device; writing "(null)" unregisters the slave device.

Reading from this file shows the name of the slave device ("(null)" if not registered).

/sys/class/spi_slave/spiB ... symlink (or actual device node) to a logical node which could hold class related state for the SPI slave controller on bus "B". When registered, a single spiB.* device is present here, possible sharing the physical SPI bus segment with other SPI slave devices.

I do not have any example C++/C code to support this off-hand.

Kiley Hykawy
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Saber
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  • That link to the doc is a 404. Someone know where to get an updated link? – Tejas Kale Oct 06 '20 at 09:07
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    @TejasKale, updated link is https://github.com/torvalds/linux/blob/master/Documentation/spi/spi-summary.rst. I already edited the answer with the new link and just waiting for approval so others can see it. – Kiley Hykawy Dec 14 '20 at 21:50
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No, Linux does not support operating as a SPI slave.

From the Overview of Linux kernel SPI support:

A "struct spi_device" encapsulates the master-side interface between those two types of driver. At this writing, Linux has no slave side programming interface.

Joseph Stine
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    Of course, you can always map the SPI registers and write code for a slave spi. So, it is possible to make a custom device that is a SPI slave. However, there is no generic infra-structure so the job is not easy. – artless noise May 06 '14 at 21:56
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The two most common examples of SPI slave implementation on Linux are the i.MX28-specific patches:

  1. Tony Lin's patch available at https://community.nxp.com/thread/325404
  2. Marek Vasut available at http://www.spinics.net/lists/arm-kernel/msg190860.html

Ishaqe Ahamed has posted some code for an SPI slave driver for OMAP2 on https://e2e.ti.com/support/embedded/linux/f/354/t/162748 but has not posted a full patch.

You might me able to get some information from Intel's Moorestown SPI Slave Controller chip driver posted at http://git.yoctoproject.org/cgit/cgit.cgi/meta-extras/plain/recipes-kernel/linux/linux-netbook-2.6.33.2/linux-2.6.34-moorestown-spi-slave-controller-driver-1.1.patch .

Note that all of these examples were done some years ago, and will need to be ported to whatever newer kernel you are using. None of the examples provides a cross-architecture framework for SPI slave drivers.

Jonathan Ben-Avraham
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