Linux-2.6.12-rc2v2.6.12-rc2

Initial git repository build. I'm not bothering with the full history,
even though we have it. We can create a separate "historical" git
archive of that later if we want to, and in the meantime it's about
3.2GB when imported into git - space that would just make the early
git days unnecessarily complicated, when we don't have a lot of good
infrastructure for it.

Let it rip!

24 files changed, 13728 insertions, 0 deletions

diff --git a/Documentation/DocBook/Makefile b/Documentation/DocBook/Makefile
new file mode 100644
index 00000000000..a221039ee4c
--- /dev/null
+++ b/Documentation/DocBook/Makefile
@@ -0,0 +1,195 @@
+###
+# This makefile is used to generate the kernel documentation,
+# primarily based on in-line comments in various source files.
+# See Documentation/kernel-doc-nano-HOWTO.txt for instruction in how
+# to ducument the SRC - and how to read it.
+# To add a new book the only step required is to add the book to the
+# list of DOCBOOKS.
+
+DOCBOOKS := wanbook.xml z8530book.xml mcabook.xml videobook.xml \
+	    kernel-hacking.xml kernel-locking.xml via-audio.xml \
+	    deviceiobook.xml procfs-guide.xml tulip-user.xml \
+	    writing_usb_driver.xml scsidrivers.xml sis900.xml \
+	    kernel-api.xml journal-api.xml lsm.xml usb.xml \
+	    gadget.xml libata.xml mtdnand.xml librs.xml
+
+###
+# The build process is as follows (targets):
+#              (xmldocs)
+# file.tmpl --> file.xml +--> file.ps   (psdocs)
+#                        +--> file.pdf  (pdfdocs)
+#                        +--> DIR=file  (htmldocs)
+#                        +--> man/      (mandocs)
+
+###
+# The targets that may be used.
+.PHONY:	xmldocs sgmldocs psdocs pdfdocs htmldocs mandocs installmandocs
+
+BOOKS := $(addprefix $(obj)/,$(DOCBOOKS))
+xmldocs: $(BOOKS)
+sgmldocs: xmldocs
+
+PS := $(patsubst %.xml, %.ps, $(BOOKS))
+psdocs: $(PS)
+
+PDF := $(patsubst %.xml, %.pdf, $(BOOKS))
+pdfdocs: $(PDF)
+
+HTML := $(patsubst %.xml, %.html, $(BOOKS))
+htmldocs: $(HTML)
+
+MAN := $(patsubst %.xml, %.9, $(BOOKS))
+mandocs: $(MAN)
+
+installmandocs: mandocs
+	$(MAKEMAN) install Documentation/DocBook/man
+
+###
+#External programs used
+KERNELDOC = scripts/kernel-doc
+DOCPROC   = scripts/basic/docproc
+SPLITMAN  = $(PERL) $(srctree)/scripts/split-man
+MAKEMAN   = $(PERL) $(srctree)/scripts/makeman
+
+###
+# DOCPROC is used for two purposes:
+# 1) To generate a dependency list for a .tmpl file
+# 2) To preprocess a .tmpl file and call kernel-doc with
+#     appropriate parameters.
+# The following rules are used to generate the .xml documentation
+# required to generate the final targets. (ps, pdf, html).
+quiet_cmd_docproc = DOCPROC $@
+      cmd_docproc = SRCTREE=$(srctree)/ $(DOCPROC) doc $< >$@
+define rule_docproc
+	set -e;								\
+        $(if $($(quiet)cmd_$(1)),echo '  $($(quiet)cmd_$(1))';) 	\
+        $(cmd_$(1)); 							\
+        ( 								\
+          echo 'cmd_$@ := $(cmd_$(1))'; 				\
+          echo $@: `SRCTREE=$(srctree) $(DOCPROC) depend $<`; 		\
+        ) > $(dir $@).$(notdir $@).cmd
+endef
+
+%.xml: %.tmpl FORCE
+	$(call if_changed_rule,docproc)
+
+###
+#Read in all saved dependency files 
+cmd_files := $(wildcard $(foreach f,$(BOOKS),$(dir $(f)).$(notdir $(f)).cmd))
+
+ifneq ($(cmd_files),)
+  include $(cmd_files)
+endif
+
+###
+# Changes in kernel-doc force a rebuild of all documentation
+$(BOOKS): $(KERNELDOC)
+
+###
+# procfs guide uses a .c file as example code.
+# This requires an explicit dependency
+C-procfs-example = procfs_example.xml
+C-procfs-example2 = $(addprefix $(obj)/,$(C-procfs-example))
+$(obj)/procfs-guide.xml: $(C-procfs-example2)
+
+###
+# Rules to generate postscript, PDF and HTML
+# db2html creates a directory. Generate a html file used for timestamp
+
+quiet_cmd_db2ps = DB2PS   $@
+      cmd_db2ps = db2ps -o $(dir $@) $<
+%.ps : %.xml
+	@(which db2ps > /dev/null 2>&1) || \
+	 (echo "*** You need to install DocBook stylesheets ***"; \
+	  exit 1)
+	$(call cmd,db2ps)
+
+quiet_cmd_db2pdf = DB2PDF  $@
+      cmd_db2pdf = db2pdf -o $(dir $@) $<
+%.pdf : %.xml
+	@(which db2pdf > /dev/null 2>&1) || \
+	 (echo "*** You need to install DocBook stylesheets ***"; \
+	  exit 1)
+	$(call cmd,db2pdf)
+
+quiet_cmd_db2html = DB2HTML $@
+      cmd_db2html = db2html -o $(patsubst %.html,%,$@) $< &&		      \
+		echo '<a HREF="$(patsubst %.html,%,$(notdir $@))/book1.html"> \
+         Goto $(patsubst %.html,%,$(notdir $@))</a><p>' > $@
+
+%.html:	%.xml
+	@(which db2html > /dev/null 2>&1) || \
+	 (echo "*** You need to install DocBook stylesheets ***"; \
+	  exit 1)
+	@rm -rf $@ $(patsubst %.html,%,$@)
+	$(call cmd,db2html)
+	@if [ ! -z "$(PNG-$(basename $(notdir $@)))" ]; then \
+            cp $(PNG-$(basename $(notdir $@))) $(patsubst %.html,%,$@); fi
+
+###
+# Rule to generate man files - output is placed in the man subdirectory
+
+%.9:	%.xml
+ifneq ($(KBUILD_SRC),)
+	$(Q)mkdir -p $(objtree)/Documentation/DocBook/man
+endif
+	$(SPLITMAN) $< $(objtree)/Documentation/DocBook/man "$(VERSION).$(PATCHLEVEL).$(SUBLEVEL)"
+	$(MAKEMAN) convert $(objtree)/Documentation/DocBook/man $<
+
+###
+# Rules to generate postscripts and PNG imgages from .fig format files
+quiet_cmd_fig2eps = FIG2EPS $@
+      cmd_fig2eps = fig2dev -Leps $< $@
+
+%.eps: %.fig
+	@(which fig2dev > /dev/null 2>&1) || \
+	 (echo "*** You need to install transfig ***"; \
+	  exit 1)
+	$(call cmd,fig2eps)
+
+quiet_cmd_fig2png = FIG2PNG $@
+      cmd_fig2png = fig2dev -Lpng $< $@
+
+%.png: %.fig
+	@(which fig2dev > /dev/null 2>&1) || \
+	 (echo "*** You need to install transfig ***"; \
+	  exit 1)
+	$(call cmd,fig2png)
+
+###
+# Rule to convert a .c file to inline XML documentation
+%.xml: %.c
+	@echo '  GEN     $@'
+	@(                            \
+	   echo "<programlisting>";   \
+	   expand --tabs=8 < $< |     \
+	   sed -e "s/&/\\&amp;/g"     \
+	       -e "s/</\\&lt;/g"      \
+	       -e "s/>/\\&gt;/g";     \
+	   echo "</programlisting>")  > $@
+
+###
+# Help targets as used by the top-level makefile
+dochelp:
+	@echo  '  Linux kernel internal documentation in different formats:'
+	@echo  '  xmldocs (XML DocBook), psdocs (Postscript), pdfdocs (PDF)'
+	@echo  '  htmldocs (HTML), mandocs (man pages, use installmandocs to install)'
+
+###
+# Temporary files left by various tools
+clean-files := $(DOCBOOKS) \
+	$(patsubst %.xml, %.dvi,  $(DOCBOOKS)) \
+	$(patsubst %.xml, %.aux,  $(DOCBOOKS)) \
+	$(patsubst %.xml, %.tex,  $(DOCBOOKS)) \
+	$(patsubst %.xml, %.log,  $(DOCBOOKS)) \
+	$(patsubst %.xml, %.out,  $(DOCBOOKS)) \
+	$(patsubst %.xml, %.ps,   $(DOCBOOKS)) \
+	$(patsubst %.xml, %.pdf,  $(DOCBOOKS)) \
+	$(patsubst %.xml, %.html, $(DOCBOOKS)) \
+	$(patsubst %.xml, %.9,    $(DOCBOOKS)) \
+	$(C-procfs-example)
+
+clean-dirs := $(patsubst %.xml,%,$(DOCBOOKS))
+
+#man put files in man subdir - traverse down
+subdir- := man/
diff --git a/Documentation/DocBook/deviceiobook.tmpl b/Documentation/DocBook/deviceiobook.tmpl
new file mode 100644
index 00000000000..6f41f2f5c6f
--- /dev/null
+++ b/Documentation/DocBook/deviceiobook.tmpl
@@ -0,0 +1,341 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN"
+	"http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []>
+
+<book id="DoingIO">
+ <bookinfo>
+  <title>Bus-Independent Device Accesses</title>
+  
+  <authorgroup>
+   <author>
+    <firstname>Matthew</firstname>
+    <surname>Wilcox</surname>
+    <affiliation>
+     <address>
+      <email>matthew@wil.cx</email>
+     </address>
+    </affiliation>
+   </author>
+  </authorgroup>
+
+  <authorgroup>
+   <author>
+    <firstname>Alan</firstname>
+    <surname>Cox</surname>
+    <affiliation>
+     <address>
+      <email>alan@redhat.com</email>
+     </address>
+    </affiliation>
+   </author>
+  </authorgroup>
+
+  <copyright>
+   <year>2001</year>
+   <holder>Matthew Wilcox</holder>
+  </copyright>
+
+  <legalnotice>
+   <para>
+     This documentation is free software; you can redistribute
+     it and/or modify it under the terms of the GNU General Public
+     License as published by the Free Software Foundation; either
+     version 2 of the License, or (at your option) any later
+     version.
+   </para>
+      
+   <para>
+     This program is distributed in the hope that it will be
+     useful, but WITHOUT ANY WARRANTY; without even the implied
+     warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+     See the GNU General Public License for more details.
+   </para>
+      
+   <para>
+     You should have received a copy of the GNU General Public
+     License along with this program; if not, write to the Free
+     Software Foundation, Inc., 59 Temple Place, Suite 330, Boston,
+     MA 02111-1307 USA
+   </para>
+      
+   <para>
+     For more details see the file COPYING in the source
+     distribution of Linux.
+   </para>
+  </legalnotice>
+ </bookinfo>
+
+<toc></toc>
+
+  <chapter id="intro">
+      <title>Introduction</title>
+  <para>
+	Linux provides an API which abstracts performing IO across all busses
+	and devices, allowing device drivers to be written independently of
+	bus type.
+  </para>
+  </chapter>
+
+  <chapter id="bugs">
+     <title>Known Bugs And Assumptions</title>
+  <para>
+	None.	
+  </para>
+  </chapter>
+
+  <chapter id="mmio">
+    <title>Memory Mapped IO</title>
+    <sect1>
+      <title>Getting Access to the Device</title>
+      <para>
+	The most widely supported form of IO is memory mapped IO.
+	That is, a part of the CPU's address space is interpreted
+	not as accesses to memory, but as accesses to a device.  Some
+	architectures define devices to be at a fixed address, but most
+	have some method of discovering devices.  The PCI bus walk is a
+	good example of such a scheme.	This document does not cover how
+	to receive such an address, but assumes you are starting with one.
+	Physical addresses are of type unsigned long. 
+      </para>
+
+      <para>
+	This address should not be used directly.  Instead, to get an
+	address suitable for passing to the accessor functions described
+	below, you should call <function>ioremap</function>.
+	An address suitable for accessing the device will be returned to you.
+      </para>
+
+      <para>
+	After you've finished using the device (say, in your module's
+	exit routine), call <function>iounmap</function> in order to return
+	the address space to the kernel.  Most architectures allocate new
+	address space each time you call <function>ioremap</function>, and
+	they can run out unless you call <function>iounmap</function>.
+      </para>
+    </sect1>
+
+    <sect1>
+      <title>Accessing the device</title>
+      <para>
+	The part of the interface most used by drivers is reading and
+	writing memory-mapped registers on the device.	Linux provides
+	interfaces to read and write 8-bit, 16-bit, 32-bit and 64-bit
+	quantities.  Due to a historical accident, these are named byte,
+	word, long and quad accesses.  Both read and write accesses are
+	supported; there is no prefetch support at this time.
+      </para>
+
+      <para>
+	The functions are named <function>readb</function>,
+	<function>readw</function>, <function>readl</function>,
+	<function>readq</function>, <function>readb_relaxed</function>,
+	<function>readw_relaxed</function>, <function>readl_relaxed</function>,
+	<function>readq_relaxed</function>, <function>writeb</function>,
+	<function>writew</function>, <function>writel</function> and
+	<function>writeq</function>.
+      </para>
+
+      <para>
+	Some devices (such as framebuffers) would like to use larger
+	transfers than 8 bytes at a time.  For these devices, the
+	<function>memcpy_toio</function>, <function>memcpy_fromio</function>
+	and <function>memset_io</function> functions are provided.
+	Do not use memset or memcpy on IO addresses; they
+	are not guaranteed to copy data in order.
+      </para>
+
+      <para>
+	The read and write functions are defined to be ordered. That is the
+	compiler is not permitted to reorder the I/O sequence. When the 
+	ordering can be compiler optimised, you can use <function>
+	__readb</function> and friends to indicate the relaxed ordering. Use 
+	this with care.
+      </para>
+
+      <para>
+	While the basic functions are defined to be synchronous with respect
+	to each other and ordered with respect to each other the busses the
+	devices sit on may themselves have asynchronicity. In particular many
+	authors are burned by the fact that PCI bus writes are posted
+	asynchronously. A driver author must issue a read from the same
+	device to ensure that writes have occurred in the specific cases the
+	author cares. This kind of property cannot be hidden from driver
+	writers in the API.  In some cases, the read used to flush the device
+	may be expected to fail (if the card is resetting, for example).  In
+	that case, the read should be done from config space, which is
+	guaranteed to soft-fail if the card doesn't respond.
+      </para>
+
+      <para>
+	The following is an example of flushing a write to a device when
+	the driver would like to ensure the write's effects are visible prior
+	to continuing execution.
+      </para>
+
+<programlisting>
+static inline void
+qla1280_disable_intrs(struct scsi_qla_host *ha)
+{
+	struct device_reg *reg;
+
+	reg = ha->iobase;
+	/* disable risc and host interrupts */
+	WRT_REG_WORD(&amp;reg->ictrl, 0);
+	/*
+	 * The following read will ensure that the above write
+	 * has been received by the device before we return from this
+	 * function.
+	 */
+	RD_REG_WORD(&amp;reg->ictrl);
+	ha->flags.ints_enabled = 0;
+}
+</programlisting>
+
+      <para>
+	In addition to write posting, on some large multiprocessing systems
+	(e.g. SGI Challenge, Origin and Altix machines) posted writes won't
+	be strongly ordered coming from different CPUs.  Thus it's important
+	to properly protect parts of your driver that do memory-mapped writes
+	with locks and use the <function>mmiowb</function> to make sure they
+	arrive in the order intended.  Issuing a regular <function>readX
+	</function> will also ensure write ordering, but should only be used
+	when the driver has to be sure that the write has actually arrived
+	at the device (not that it's simply ordered with respect to other
+	writes), since a full <function>readX</function> is a relatively
+	expensive operation.
+      </para>
+
+      <para>
+	Generally, one should use <function>mmiowb</function> prior to
+	releasing a spinlock that protects regions using <function>writeb
+	</function> or similar functions that aren't surrounded by <function>
+	readb</function> calls, which will ensure ordering and flushing.  The
+	following pseudocode illustrates what might occur if write ordering
+	isn't guaranteed via <function>mmiowb</function> or one of the
+	<function>readX</function> functions.
+      </para>
+
+<programlisting>
+CPU A:  spin_lock_irqsave(&amp;dev_lock, flags)
+CPU A:  ...
+CPU A:  writel(newval, ring_ptr);
+CPU A:  spin_unlock_irqrestore(&amp;dev_lock, flags)
+        ...
+CPU B:  spin_lock_irqsave(&amp;dev_lock, flags)
+CPU B:  writel(newval2, ring_ptr);
+CPU B:  ...
+CPU B:  spin_unlock_irqrestore(&amp;dev_lock, flags)
+</programlisting>
+
+      <para>
+	In the case above, newval2 could be written to ring_ptr before
+	newval.  Fixing it is easy though:
+      </para>
+
+<programlisting>
+CPU A:  spin_lock_irqsave(&amp;dev_lock, flags)
+CPU A:  ...
+CPU A:  writel(newval, ring_ptr);
+CPU A:  mmiowb(); /* ensure no other writes beat us to the device */
+CPU A:  spin_unlock_irqrestore(&amp;dev_lock, flags)
+        ...
+CPU B:  spin_lock_irqsave(&amp;dev_lock, flags)
+CPU B:  writel(newval2, ring_ptr);
+CPU B:  ...
+CPU B:  mmiowb();
+CPU B:  spin_unlock_irqrestore(&amp;dev_lock, flags)
+</programlisting>
+
+      <para>
+	See tg3.c for a real world example of how to use <function>mmiowb
+	</function>
+      </para>
+
+      <para>
+	PCI ordering rules also guarantee that PIO read responses arrive
+	after any outstanding DMA writes from that bus, since for some devices
+	the result of a <function>readb</function> call may signal to the
+	driver that a DMA transaction is complete.  In many cases, however,
+	the driver may want to indicate that the next
+	<function>readb</function> call has no relation to any previous DMA
+	writes performed by the device.  The driver can use
+	<function>readb_relaxed</function> for these cases, although only
+	some platforms will honor the relaxed semantics.  Using the relaxed
+	read functions will provide significant performance benefits on
+	platforms that support it.  The qla2xxx driver provides examples
+	of how to use <function>readX_relaxed</function>.  In many cases,
+	a majority of the driver's <function>readX</function> calls can
+	safely be converted to <function>readX_relaxed</function> calls, since
+	only a few will indicate or depend on DMA completion.
+      </para>
+    </sect1>
+
+    <sect1>
+      <title>ISA legacy functions</title>
+      <para>
+	On older kernels (2.2 and earlier) the ISA bus could be read or
+	written with these functions and without ioremap being used. This is
+	no longer true in Linux 2.4. A set of equivalent functions exist for
+	easy legacy driver porting. The functions available are prefixed
+	with 'isa_' and are <function>isa_readb</function>,
+	<function>isa_writeb</function>, <function>isa_readw</function>, 
+	<function>isa_writew</function>, <function>isa_readl</function>,
+	<function>isa_writel</function>, <function>isa_memcpy_fromio</function>
+	and <function>isa_memcpy_toio</function>
+      </para>
+      <para>
+	These functions should not be used in new drivers, and will
+	eventually be going away.
+      </para>
+    </sect1>
+
+  </chapter>
+
+  <chapter>
+    <title>Port Space Accesses</title>
+    <sect1>
+      <title>Port Space Explained</title>
+
+      <para>
+	Another form of IO commonly supported is Port Space.  This is a
+	range of addresses separate to the normal memory address space.
+	Access to these addresses is generally not as fast as accesses
+	to the memory mapped addresses, and it also has a potentially
+	smaller address space.
+      </para>
+
+      <para>
+	Unlike memory mapped IO, no preparation is required
+	to access port space.
+      </para>
+
+    </sect1>
+    <sect1>
+      <title>Accessing Port Space</title>
+      <para>
+	Accesses to this space are provided through a set of functions
+	which allow 8-bit, 16-bit and 32-bit accesses; also
+	known as byte, word and long.  These functions are
+	<function>inb</function>, <function>inw</function>,
+	<function>inl</function>, <function>outb</function>,
+	<function>outw</function> and <function>outl</function>.
+      </para>
+
+      <para>
+	Some variants are provided for these functions.  Some devices
+	require that accesses to their ports are slowed down.  This
+	functionality is provided by appending a <function>_p</function>
+	to the end of the function.  There are also equivalents to memcpy.
+	The <function>ins</function> and <function>outs</function>
+	functions copy bytes, words or longs to the given port.
+      </para>
+    </sect1>
+
+  </chapter>
+
+  <chapter id="pubfunctions">
+     <title>Public Functions Provided</title>
+!Einclude/asm-i386/io.h
+  </chapter>
+
+</book>
diff --git a/Documentation/DocBook/gadget.tmpl b/Documentation/DocBook/gadget.tmpl
new file mode 100644
index 00000000000..a3444243612
--- /dev/null
+++ b/Documentation/DocBook/gadget.tmpl
@@ -0,0 +1,752 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN"
+	"http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []>
+
+<book id="USB-Gadget-API">
+  <bookinfo>
+    <title>USB Gadget API for Linux</title>
+    <date>20 August 2004</date>
+    <edition>20 August 2004</edition>
+  
+    <legalnotice>
+       <para>
+	 This documentation is free software; you can redistribute
+	 it and/or modify it under the terms of the GNU General Public
+	 License as published by the Free Software Foundation; either
+	 version 2 of the License, or (at your option) any later
+	 version.
+       </para>
+	  
+       <para>
+	 This program is distributed in the hope that it will be
+	 useful, but WITHOUT ANY WARRANTY; without even the implied
+	 warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+	 See the GNU General Public License for more details.
+       </para>
+	  
+       <para>
+	 You should have received a copy of the GNU General Public
+	 License along with this program; if not, write to the Free
+	 Software Foundation, Inc., 59 Temple Place, Suite 330, Boston,
+	 MA 02111-1307 USA
+       </para>
+	  
+       <para>
+	 For more details see the file COPYING in the source
+	 distribution of Linux.
+       </para>
+    </legalnotice>
+    <copyright>
+      <year>2003-2004</year>
+      <holder>David Brownell</holder>
+    </copyright>
+
+    <author>
+      <firstname>David</firstname> 
+      <surname>Brownell</surname>
+      <affiliation>
+        <address><email>dbrownell@users.sourceforge.net</email></address>
+      </affiliation>
+    </author>
+  </bookinfo>
+
+<toc></toc>
+
+<chapter><title>Introduction</title>
+
+<para>This document presents a Linux-USB "Gadget"
+kernel mode
+API, for use within peripherals and other USB devices
+that embed Linux.
+It provides an overview of the API structure,
+and shows how that fits into a system development project.
+This is the first such API released on Linux to address
+a number of important problems, including: </para>
+
+<itemizedlist>
+    <listitem><para>Supports USB 2.0, for high speed devices which
+	can stream data at several dozen megabytes per second.
+	</para></listitem>
+    <listitem><para>Handles devices with dozens of endpoints just as
+	well as ones with just two fixed-function ones.  Gadget drivers
+	can be written so they're easy to port to new hardware.
+	</para></listitem>
+    <listitem><para>Flexible enough to expose more complex USB device
+	capabilities such as multiple configurations, multiple interfaces,
+	composite devices,
+	and alternate interface settings.
+	</para></listitem>
+    <listitem><para>USB "On-The-Go" (OTG) support, in conjunction
+	with updates to the Linux-USB host side.
+	</para></listitem>
+    <listitem><para>Sharing data structures and API models with the
+	Linux-USB host side API.  This helps the OTG support, and
+	looks forward to more-symmetric frameworks (where the same
+	I/O model is used by both host and device side drivers).
+	</para></listitem>
+    <listitem><para>Minimalist, so it's easier to support new device
+	controller hardware.  I/O processing doesn't imply large
+	demands for memory or CPU resources.
+	</para></listitem>
+</itemizedlist>
+
+
+<para>Most Linux developers will not be able to use this API, since they
+have USB "host" hardware in a PC, workstation, or server.
+Linux users with embedded systems are more likely to
+have USB peripheral hardware.
+To distinguish drivers running inside such hardware from the
+more familiar Linux "USB device drivers",
+which are host side proxies for the real USB devices,
+a different term is used:
+the drivers inside the peripherals are "USB gadget drivers".
+In USB protocol interactions, the device driver is the master
+(or "client driver")
+and the gadget driver is the slave (or "function driver").
+</para>
+
+<para>The gadget API resembles the host side Linux-USB API in that both
+use queues of request objects to package I/O buffers, and those requests
+may be submitted or canceled.
+They share common definitions for the standard USB
+<emphasis>Chapter 9</emphasis> messages, structures, and constants.
+Also, both APIs bind and unbind drivers to devices.
+The APIs differ in detail, since the host side's current
+URB framework exposes a number of implementation details
+and assumptions that are inappropriate for a gadget API.
+While the model for control transfers and configuration
+management is necessarily different (one side is a hardware-neutral master,
+the other is a hardware-aware slave), the endpoint I/0 API used here
+should also be usable for an overhead-reduced host side API.
+</para>
+
+</chapter>
+
+<chapter id="structure"><title>Structure of Gadget Drivers</title>
+
+<para>A system running inside a USB peripheral
+normally has at least three layers inside the kernel to handle
+USB protocol processing, and may have additional layers in
+user space code.
+The "gadget" API is used by the middle layer to interact
+with the lowest level (which directly handles hardware).
+</para>
+
+<para>In Linux, from the bottom up, these layers are:
+</para>
+
+<variablelist>
+
+    <varlistentry>
+        <term><emphasis>USB Controller Driver</emphasis></term>
+
+	<listitem>
+	<para>This is the lowest software level.
+	It is the only layer that talks to hardware,
+	through registers, fifos, dma, irqs, and the like.
+	The <filename>&lt;linux/usb_gadget.h&gt;</filename> API abstracts
+	the peripheral controller endpoint hardware.
+	That hardware is exposed through endpoint objects, which accept
+	streams of IN/OUT buffers, and through callbacks that interact
+	with gadget drivers.
+	Since normal USB devices only have one upstream
+	port, they only have one of these drivers.
+	The controller driver can support any number of different
+	gadget drivers, but only one of them can be used at a time.
+	</para>
+
+	<para>Examples of such controller hardware include
+	the PCI-based NetChip 2280 USB 2.0 high speed controller,
+	the SA-11x0 or PXA-25x UDC (found within many PDAs),
+	and a variety of other products.
+	</para>
+
+	</listitem></varlistentry>
+
+    <varlistentry>
+	<term><emphasis>Gadget Driver</emphasis></term>
+
+	<listitem>
+	<para>The lower boundary of this driver implements hardware-neutral
+	USB functions, using calls to the controller driver.
+	Because such hardware varies widely in capabilities and restrictions,
+	and is used in embedded environments where space is at a premium,
+	the gadget driver is often configured at compile time
+	to work with endpoints supported by one particular controller.
+	Gadget drivers may be portable to several different controllers,
+	using conditional compilation.
+	(Recent kernels substantially simplify the work involved in
+	supporting new hardware, by <emphasis>autoconfiguring</emphasis>
+	endpoints automatically for many bulk-oriented drivers.)
+	Gadget driver responsibilities include:
+	</para>
+	<itemizedlist>
+	    <listitem><para>handling setup requests (ep0 protocol responses)
+		possibly including class-specific functionality
+		</para></listitem>
+	    <listitem><para>returning configuration and string descriptors
+		</para></listitem>
+	    <listitem><para>(re)setting configurations and interface
+		altsettings, including enabling and configuring endpoints
+		</para></listitem>
+	    <listitem><para>handling life cycle events, such as managing
+		bindings to hardware,
+		USB suspend/resume, remote wakeup,
+		and disconnection from the USB host.
+		</para></listitem>
+	    <listitem><para>managing IN and OUT transfers on all currently
+		enabled endpoints
+		</para></listitem>
+	</itemizedlist>
+
+	<para>
+	Such drivers may be modules of proprietary code, although
+	that approach is discouraged in the Linux community.
+	</para>
+	</listitem></varlistentry>
+
+    <varlistentry>
+	<term><emphasis>Upper Level</emphasis></term>
+
+	<listitem>
+	<para>Most gadget drivers have an upper boundary that connects
+	to some Linux driver or framework in Linux.
+	Through that boundary flows the data which the gadget driver
+	produces and/or consumes through protocol transfers over USB.
+	Examples include:
+	</para>
+	<itemizedlist>
+	    <listitem><para>user mode code, using generic (gadgetfs)
+	        or application specific files in
+		<filename>/dev</filename>
+		</para></listitem>
+	    <listitem><para>networking subsystem (for network gadgets,
+		like the CDC Ethernet Model gadget driver)
+		</para></listitem>
+	    <listitem><para>data capture drivers, perhaps video4Linux or
+		 a scanner driver; or test and measurement hardware.
+		 </para></listitem>
+	    <listitem><para>input subsystem (for HID gadgets)
+		</para></listitem>
+	    <listitem><para>sound subsystem (for audio gadgets)
+		</para></listitem>
+	    <listitem><para>file system (for PTP gadgets)
+		</para></listitem>
+	    <listitem><para>block i/o subsystem (for usb-storage gadgets)
+		</para></listitem>
+	    <listitem><para>... and more </para></listitem>
+	</itemizedlist>
+	</listitem></varlistentry>
+
+    <varlistentry>
+	<term&