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spi: Document SPI slave controller support 

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Mark Brown <broonie@kernel.org>
This commit is contained in:
Geert Uytterhoeven 2017-05-22 15:11:42 +02:00 committed by Mark Brown
parent 6c364062bf
commit aa2ea9115b
1 changed files with 20 additions and 7 deletions
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27
Documentation/spi/spi-summary
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@ -62,8 +62,8 @@ chips described as using "three wire" signaling: SCK, data, nCSx.
(That data line is sometimes called MOMI or SISO.)
Microcontrollers often support both master and slave sides of the SPI
protocol. This document (and Linux) currently only supports the master
side of SPI interactions.
protocol. This document (and Linux) supports both the master and slave
sides of SPI interactions.
Who uses it? On what kinds of systems?
@ -154,9 +154,8 @@ control audio interfaces, present touchscreen sensors as input interfaces,
or monitor temperature and voltage levels during industrial processing.
And those might all be sharing the same controller driver.
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.
A "struct spi_device" encapsulates the controller-side interface between
those two types of drivers.
There is a minimal core of SPI programming interfaces, focussing on
using the driver model to connect controller and protocol drivers using
@ -177,10 +176,24 @@ shows up in sysfs in several locations:
/sys/bus/spi/drivers/D ... driver for one or more spi*.* devices
/sys/class/spi_master/spiB ... symlink (or actual device node) to
a logical node which could hold class related state for the
controller managing bus "B". All spiB.* devices share one
a logical node which could hold class related state for the SPI
master controller managing bus "B". All spiB.* devices share one
physical SPI bus segment, with SCLK, MOSI, and MISO.
/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.
Note that the actual location of the controller's class state depends
on whether you enabled CONFIG_SYSFS_DEPRECATED or not. At this time,
the only class-specific state is the bus number ("B" in "spiB"), so