X-Git-Url: http://pilppa.org/gitweb/gitweb.cgi?a=blobdiff_plain;f=Documentation%2FDocBook%2Fkernel-api.tmpl;h=a2b2b4d187c5c75a9312112fb9fc361159acd20b;hb=36f021b579d195cdc5fa6f3e2bab198b4bf70643;hp=b61dfc79e1b87904b4280ad8a9fba47b733e0bef;hpb=e0cc09e295f346b7921e921f385fe5213472316a;p=linux-2.6-omap-h63xx.git

diff --git a/Documentation/DocBook/kernel-api.tmpl b/Documentation/DocBook/kernel-api.tmpl
index b61dfc79e1b..a2b2b4d187c 100644
--- a/Documentation/DocBook/kernel-api.tmpl
+++ b/Documentation/DocBook/kernel-api.tmpl
@@ -576,4 +576,67 @@ X!Idrivers/video/console/fonts.c
 !Edrivers/input/ff-core.c
 !Edrivers/input/ff-memless.c
   </chapter>
+
+  <chapter id="spi">
+      <title>Serial Peripheral Interface (SPI)</title>
+  <para>
+	SPI is the "Serial Peripheral Interface", widely used with
+	embedded systems because it is a simple and efficient
+	interface:  basically a multiplexed shift register.
+	Its three signal wires hold a clock (SCK, often in the range
+	of 1-20 MHz), a "Master Out, Slave In" (MOSI) data line, and
+	a "Master In, Slave Out" (MISO) data line.
+	SPI is a full duplex protocol; for each bit shifted out the
+	MOSI line (one per clock) another is shifted in on the MISO line.
+	Those bits are assembled into words of various sizes on the
+	way to and from system memory.
+	An additional chipselect line is usually active-low (nCS);
+	four signals are normally used for each peripheral, plus
+	sometimes an interrupt.
+  </para>
+  <para>
+	The SPI bus facilities listed here provide a generalized
+	interface to declare SPI busses and devices, manage them
+	according to the standard Linux driver model, and perform
+	input/output operations.
+	At this time, only "master" side interfaces are supported,
+	where Linux talks to SPI peripherals and does not implement
+	such a peripheral itself.
+	(Interfaces to support implementing SPI slaves would
+	necessarily look different.)
+  </para>
+  <para>
+	The programming interface is structured around two kinds of driver,
+	and two kinds of device.
+	A "Controller Driver" abstracts the controller hardware, which may
+	be as simple as a set of GPIO pins or as complex as a pair of FIFOs
+	connected to dual DMA engines on the other side of the SPI shift
+	register (maximizing throughput).  Such drivers bridge between
+	whatever bus they sit on (often the platform bus) and SPI, and
+	expose the SPI side of their device as a
+	<structname>struct spi_master</structname>.
+	SPI devices are children of that master, represented as a
+	<structname>struct spi_device</structname> and manufactured from
+	<structname>struct spi_board_info</structname> descriptors which
+	are usually provided by board-specific initialization code.
+	A <structname>struct spi_driver</structname> is called a
+	"Protocol Driver", and is bound to a spi_device using normal
+	driver model calls.
+  </para>
+  <para>
+	The I/O model is a set of queued messages.  Protocol drivers
+	submit one or more <structname>struct spi_message</structname>
+	objects, which are processed and completed asynchronously.
+	(There are synchronous wrappers, however.)  Messages are
+	built from one or more <structname>struct spi_transfer</structname>
+	objects, each of which wraps a full duplex SPI transfer.
+	A variety of protocol tweaking options are needed, because
+	different chips adopt very different policies for how they
+	use the bits transferred with SPI.
+  </para>
+!Iinclude/linux/spi/spi.h
+!Fdrivers/spi/spi.c spi_register_board_info
+!Edrivers/spi/spi.c
+  </chapter>
+
 </book>