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From 0be2c71f293e8c8423e5378cc73f71e10205ad54 Mon Sep 17 00:00:00 2001
From: Geert Uytterhoeven <geert+renesas@glider.be>
Date: Thu, 8 Sep 2016 15:01:48 +0200
Subject: [PATCH 3/7] spi: Document SPI slave controller support
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
---
Documentation/spi/spi-summary | 27 ++++++++++++++++++++-------
1 file changed, 20 insertions(+), 7 deletions(-)
diff --git a/Documentation/spi/spi-summary b/Documentation/spi/spi-summary
index d1824b3..1721c1b 100644
--- a/Documentation/spi/spi-summary
+++ b/Documentation/spi/spi-summary
@@ -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
--
1.7.10.4
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