diff options
Diffstat (limited to 'Documentation/spi/spi-summary')
| -rw-r--r-- | Documentation/spi/spi-summary | 27 |
1 files changed, 20 insertions, 7 deletions
diff --git a/Documentation/spi/spi-summary b/Documentation/spi/spi-summary index d1824b399b2d..1721c1b570c3 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 |