A-Team_Digital_Solutions/android_kernel_motorola_sm6375
Watch
2
0
Fork
You've already forked android_kernel_motorola_sm6375
 0
mirror of https://github.com/BobTheBlinker/android_kernel_motorola_sm6375.git synced 2026-10-28 18:51:56 -04:00
Code Issues Projects Releases Packages Wiki Activity

A slightly quieter cycle for documentation this time around.

Browse source 
Three more DocBook template files have been converted to RST; only 21 to
 go.  There are various build improvements and the usual array of
 documentation improvements and fixes.
 -----BEGIN PGP SIGNATURE-----
 
 iQIcBAABAgAGBQJYriFXAAoJEI3ONVYwIuV6iTMP/iV7ownq9IK1f8askcXKM76i
 NoRdj4/JywAPQ73vLhOSDVELGdVJNRBjdyOdBRzxPgsqAhFmm79lVYV2eLIffQ2k
 7LcVbEQR77I+4z9SwqIVbIWNCBry7Hu8aWh7moDL3I6yeuay408yr5YW2lIlsqHZ
 V/LZgkTWDe+iQPeXNA4Djzylx0lcRlAy4yMSLjN1+gb9/uBnXb9J0eGJzgfZfrL8
 fiIhymg3bv8vB99l6LMR5vT343QLWXf1yS31A7rPQvwkDo6zFehUJA0XNfIsl2dw
 VQYsvl9vp9wy3e6Y0qKXPn1XhAhCrm64P3crBxK31MMvcKZVCfeRSZ78wrvpvewy
 MVLlXdqop1bHPHowtRfA5jwxr1NqcYp+Jg0+YGX3iXpPi1Jfk36DNUy9iWvtvIzr
 lWgQcIKsdCwwYUcvPR8Kt8T/3q/AHbYlI6mimWlkmbZwncQcgCrH5xSG+c2BIPfV
 fn3W6eLHBn8RyVsxlaXlA0Y9TNtI/Cm85b3Ri10pFvhl868ppWfJxXHi7UtcbU58
 sQzahISCTXOH/NQwkkh7kFMtczbB43rAcChvF7EUYpazVBpJ4P4HxKFg3eIzIdc6
 VlBSaMu1hxUGoYxNNYuKr/nYstuczLOKzK7q4j/JOExY3RgTWP+T3bF02wgubvoa
 D/9WfScewkgCJRoA7i17
 =C5nd
 -----END PGP SIGNATURE-----

Merge tag 'docs-4.11' of git://git.lwn.net/linux

Pull documentation updates from Jonathan Corbet:
 "A slightly quieter cycle for documentation this time around.

  Three more DocBook template files have been converted to RST; only 21
  to go. There are various build improvements and the usual array of
  documentation improvements and fixes"

* tag 'docs-4.11' of git://git.lwn.net/linux: (44 commits)
  docs / driver-api: Fix structure references in device_link.rst
  PM / docs: Fix structure references in device.rst
  Add a target to check broken external links in the Documentation
  Documentation: Fix linux-api list typo
  Documentation: DocBook/Makefile comment typo
  Improve sparse documentation
  Documentation: make Makefile.sphinx no-ops quieter
  Documentation: DMA-ISA-LPC.txt
  Documentation: input: fix path to input code definitions
  docs: Remove the copyright year from conf.py
  docs: Fix a warning in the Korean HOWTO.rst translation
  PM / sleep / docs: Convert PM notifiers document to reST
  PM / core / docs: Convert sleep states API document to reST
  PM / core: Update kerneldoc comments in pm.h
  doc-rst: Fix recursive make invocation from macros
  doc-rst: Delete output of failed dot-SVG conversion
  doc-rst: Break shell command sequences on failure
  Documentation/sphinx: make targets independent of Sphinx work for HAVE_SPHINX=0
  doc-rst: fixed cleandoc target when used with O=dir
  Documentation/sphinx: prevent generation of .pyc files in the source tree
  ...
This commit is contained in:
Linus Torvalds 2017-02-22 18:51:29 -08:00
commit c1aac62f36
56 changed files with 3288 additions and 3510 deletions
Download patch file Download diff file Expand all files Collapse all files

5
Documentation/DocBook/Makefile
View file

@ -13,7 +13,7 @@ DOCBOOKS := z8530book.xml \
gadget.xml libata.xml mtdnand.xml librs.xml rapidio.xml \
genericirq.xml s390-drivers.xml scsi.xml \
sh.xml regulator.xml w1.xml \
writing_musb_glue_layer.xml iio.xml
writing_musb_glue_layer.xml
ifeq ($(DOCBOOKS),)
@ -71,6 +71,7 @@ installmandocs: mandocs
# no-op for the DocBook toolchain
epubdocs:
latexdocs:
linkcheckdocs:
###
#External programs used
@ -272,6 +273,6 @@ cleandocs:
$(Q)rm -rf $(call objectify, $(clean-dirs))
# Declare the contents of the .PHONY variable as phony. We keep that
# information in a variable se we can use it in if_changed and friends.
# information in a variable so we can use it in if_changed and friends.
.PHONY: $(PHONY)

323
Documentation/DocBook/deviceiobook.tmpl
View file

@ -1,323 +0,0 @@
<?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>[email protected]</email>
</address>
</affiliation>
</author>
</authorgroup>
<authorgroup>
<author>
<firstname>Alan</firstname>
<surname>Cox</surname>
<affiliation>
<address>
<email>[email protected]</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 id="getting_access_to_the_device">
<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 id="accessing_the_device">
<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>
</chapter>
<chapter id="port_space_accesses">
<title>Port Space Accesses</title>
<sect1 id="port_space_explained">
<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 id="accessing_port_space">
<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>
!Iarch/x86/include/asm/io.h
!Elib/pci_iomap.c
</chapter>
</book>

697
Documentation/DocBook/iio.tmpl
View file

@ -1,697 +0,0 @@
<?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="iioid">
<bookinfo>
<title>Industrial I/O driver developer's guide </title>
<authorgroup>
<author>
<firstname>Daniel</firstname>
<surname>Baluta</surname>
<affiliation>
<address>
<email>[email protected]</email>
</address>
</affiliation>
</author>
</authorgroup>
<copyright>
<year>2015</year>
<holder>Intel Corporation</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 version 2.
</para>
</legalnotice>
</bookinfo>
<toc></toc>
<chapter id="intro">
<title>Introduction</title>
<para>
The main purpose of the Industrial I/O subsystem (IIO) is to provide
support for devices that in some sense perform either analog-to-digital
conversion (ADC) or digital-to-analog conversion (DAC) or both. The aim
is to fill the gap between the somewhat similar hwmon and input
subsystems.
Hwmon is directed at low sample rate sensors used to monitor and
control the system itself, like fan speed control or temperature
measurement. Input is, as its name suggests, focused on human interaction
input devices (keyboard, mouse, touchscreen). In some cases there is
considerable overlap between these and IIO.
</para>
<para>
Devices that fall into this category include:
<itemizedlist>
<listitem>
analog to digital converters (ADCs)
</listitem>
<listitem>
accelerometers
</listitem>
<listitem>
capacitance to digital converters (CDCs)
</listitem>
<listitem>
digital to analog converters (DACs)
</listitem>
<listitem>
gyroscopes
</listitem>
<listitem>
inertial measurement units (IMUs)
</listitem>
<listitem>
color and light sensors
</listitem>
<listitem>
magnetometers
</listitem>
<listitem>
pressure sensors
</listitem>
<listitem>
proximity sensors
</listitem>
<listitem>
temperature sensors
</listitem>
</itemizedlist>
Usually these sensors are connected via SPI or I2C. A common use case of the
sensors devices is to have combined functionality (e.g. light plus proximity
sensor).
</para>
</chapter>
<chapter id='iiosubsys'>
<title>Industrial I/O core</title>
<para>
The Industrial I/O core offers:
<itemizedlist>
<listitem>
a unified framework for writing drivers for many different types of
embedded sensors.
</listitem>
<listitem>
a standard interface to user space applications manipulating sensors.
</listitem>
</itemizedlist>
The implementation can be found under <filename>
drivers/iio/industrialio-*</filename>
</para>
<sect1 id="iiodevice">
<title> Industrial I/O devices </title>
!Finclude/linux/iio/iio.h iio_dev
!Fdrivers/iio/industrialio-core.c iio_device_alloc
!Fdrivers/iio/industrialio-core.c iio_device_free
!Fdrivers/iio/industrialio-core.c iio_device_register
!Fdrivers/iio/industrialio-core.c iio_device_unregister
<para>
An IIO device usually corresponds to a single hardware sensor and it
provides all the information needed by a driver handling a device.
Let's first have a look at the functionality embedded in an IIO
device then we will show how a device driver makes use of an IIO
device.
</para>
<para>
There are two ways for a user space application to interact
with an IIO driver.
<itemizedlist>
<listitem>
<filename>/sys/bus/iio/iio:deviceX/</filename>, this
represents a hardware sensor and groups together the data
channels of the same chip.
</listitem>
<listitem>
<filename>/dev/iio:deviceX</filename>, character device node
interface used for buffered data transfer and for events information
retrieval.
</listitem>
</itemizedlist>
</para>
A typical IIO driver will register itself as an I2C or SPI driver and will
create two routines, <function> probe </function> and <function> remove
</function>. At <function>probe</function>:
<itemizedlist>
<listitem>call <function>iio_device_alloc</function>, which allocates memory
for an IIO device.
</listitem>
<listitem> initialize IIO device fields with driver specific information
(e.g. device name, device channels).
</listitem>
<listitem>call <function> iio_device_register</function>, this registers the
device with the IIO core. After this call the device is ready to accept
requests from user space applications.
</listitem>
</itemizedlist>
At <function>remove</function>, we free the resources allocated in
<function>probe</function> in reverse order:
<itemizedlist>
<listitem><function>iio_device_unregister</function>, unregister the device
from the IIO core.
</listitem>
<listitem><function>iio_device_free</function>, free the memory allocated
for the IIO device.
</listitem>
</itemizedlist>
<sect2 id="iioattr"> <title> IIO device sysfs interface </title>
<para>
Attributes are sysfs files used to expose chip info and also allowing
applications to set various configuration parameters. For device
with index X, attributes can be found under
<filename>/sys/bus/iio/iio:deviceX/ </filename> directory.
Common attributes are:
<itemizedlist>
<listitem><filename>name</filename>, description of the physical
chip.
</listitem>
<listitem><filename>dev</filename>, shows the major:minor pair
associated with <filename>/dev/iio:deviceX</filename> node.
</listitem>
<listitem><filename>sampling_frequency_available</filename>,
available discrete set of sampling frequency values for
device.
</listitem>
</itemizedlist>
Available standard attributes for IIO devices are described in the
<filename>Documentation/ABI/testing/sysfs-bus-iio </filename> file
in the Linux kernel sources.
</para>
</sect2>
<sect2 id="iiochannel"> <title> IIO device channels </title>
!Finclude/linux/iio/iio.h iio_chan_spec structure.
<para>
An IIO device channel is a representation of a data channel. An
IIO device can have one or multiple channels. For example:
<itemizedlist>
<listitem>
a thermometer sensor has one channel representing the
temperature measurement.
</listitem>
<listitem>
a light sensor with two channels indicating the measurements in
the visible and infrared spectrum.
</listitem>
<listitem>
an accelerometer can have up to 3 channels representing
acceleration on X, Y and Z axes.
</listitem>
</itemizedlist>
An IIO channel is described by the <type> struct iio_chan_spec
</type>. A thermometer driver for the temperature sensor in the
example above would have to describe its channel as follows:
<programlisting>
static const struct iio_chan_spec temp_channel[] = {
{
.type = IIO_TEMP,
.info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED),
},
};
</programlisting>
Channel sysfs attributes exposed to userspace are specified in
the form of <emphasis>bitmasks</emphasis>. Depending on their
shared info, attributes can be set in one of the following masks:
<itemizedlist>
<listitem><emphasis>info_mask_separate</emphasis>, attributes will
be specific to this channel</listitem>
<listitem><emphasis>info_mask_shared_by_type</emphasis>,
attributes are shared by all channels of the same type</listitem>
<listitem><emphasis>info_mask_shared_by_dir</emphasis>, attributes
are shared by all channels of the same direction </listitem>
<listitem><emphasis>info_mask_shared_by_all</emphasis>,
attributes are shared by all channels</listitem>
</itemizedlist>
When there are multiple data channels per channel type we have two
ways to distinguish between them:
<itemizedlist>
<listitem> set <emphasis> .modified</emphasis> field of <type>
iio_chan_spec</type> to 1. Modifiers are specified using
<emphasis>.channel2</emphasis> field of the same
<type>iio_chan_spec</type> structure and are used to indicate a
physically unique characteristic of the channel such as its direction
or spectral response. For example, a light sensor can have two channels,
one for infrared light and one for both infrared and visible light.
</listitem>
<listitem> set <emphasis>.indexed </emphasis> field of
<type>iio_chan_spec</type> to 1. In this case the channel is
simply another instance with an index specified by the
<emphasis>.channel</emphasis> field.
</listitem>
</itemizedlist>
Here is how we can make use of the channel's modifiers:
<programlisting>
static const struct iio_chan_spec light_channels[] = {
{
.type = IIO_INTENSITY,
.modified = 1,
.channel2 = IIO_MOD_LIGHT_IR,
.info_mask_separate = BIT(IIO_CHAN_INFO_RAW),
.info_mask_shared = BIT(IIO_CHAN_INFO_SAMP_FREQ),
},
{
.type = IIO_INTENSITY,
.modified = 1,
.channel2 = IIO_MOD_LIGHT_BOTH,
.info_mask_separate = BIT(IIO_CHAN_INFO_RAW),
.info_mask_shared = BIT(IIO_CHAN_INFO_SAMP_FREQ),
},
{
.type = IIO_LIGHT,
.info_mask_separate = BIT(IIO_CHAN_INFO_PROCESSED),
.info_mask_shared = BIT(IIO_CHAN_INFO_SAMP_FREQ),
},
}
</programlisting>
This channel's definition will generate two separate sysfs files
for raw data retrieval:
<itemizedlist>
<listitem>
<filename>/sys/bus/iio/iio:deviceX/in_intensity_ir_raw</filename>
</listitem>
<listitem>
<filename>/sys/bus/iio/iio:deviceX/in_intensity_both_raw</filename>
</listitem>
</itemizedlist>
one file for processed data:
<itemizedlist>
<listitem>
<filename>/sys/bus/iio/iio:deviceX/in_illuminance_input
</filename>
</listitem>
</itemizedlist>
and one shared sysfs file for sampling frequency:
<itemizedlist>
<listitem>
<filename>/sys/bus/iio/iio:deviceX/sampling_frequency.
</filename>
</listitem>
</itemizedlist>
</para>
<para>
Here is how we can make use of the channel's indexing:
<programlisting>
static const struct iio_chan_spec light_channels[] = {
{
.type = IIO_VOLTAGE,
.indexed = 1,
.channel = 0,
.info_mask_separate = BIT(IIO_CHAN_INFO_RAW),
},
{
.type = IIO_VOLTAGE,
.indexed = 1,
.channel = 1,
.info_mask_separate = BIT(IIO_CHAN_INFO_RAW),
},
}
</programlisting>
This will generate two separate attributes files for raw data
retrieval:
<itemizedlist>
<listitem>
<filename>/sys/bus/iio/devices/iio:deviceX/in_voltage0_raw</filename>,
representing voltage measurement for channel 0.
</listitem>
<listitem>
<filename>/sys/bus/iio/devices/iio:deviceX/in_voltage1_raw</filename>,
representing voltage measurement for channel 1.
</listitem>
</itemizedlist>
</para>
</sect2>
</sect1>
<sect1 id="iiobuffer"> <title> Industrial I/O buffers </title>
!Finclude/linux/iio/buffer.h iio_buffer
!Edrivers/iio/industrialio-buffer.c
<para>
The Industrial I/O core offers a way for continuous data capture
based on a trigger source. Multiple data channels can be read at once
from <filename>/dev/iio:deviceX</filename> character device node,
thus reducing the CPU load.
</para>
<sect2 id="iiobuffersysfs">
<title>IIO buffer sysfs interface </title>
<para>
An IIO buffer has an associated attributes directory under <filename>
/sys/bus/iio/iio:deviceX/buffer/</filename>. Here are the existing
attributes:
<itemizedlist>
<listitem>
<emphasis>length</emphasis>, the total number of data samples
(capacity) that can be stored by the buffer.
</listitem>
<listitem>
<emphasis>enable</emphasis>, activate buffer capture.
</listitem>
</itemizedlist>
</para>
</sect2>
<sect2 id="iiobuffersetup"> <title> IIO buffer setup </title>
<para>The meta information associated with a channel reading
placed in a buffer is called a <emphasis> scan element </emphasis>.
The important bits configuring scan elements are exposed to
userspace applications via the <filename>
/sys/bus/iio/iio:deviceX/scan_elements/</filename> directory. This
file contains attributes of the following form:
<itemizedlist>
<listitem><emphasis>enable</emphasis>, used for enabling a channel.
If and only if its attribute is non zero, then a triggered capture
will contain data samples for this channel.
</listitem>
<listitem><emphasis>type</emphasis>, description of the scan element
data storage within the buffer and hence the form in which it is
read from user space. Format is <emphasis>
[be|le]:[s|u]bits/storagebitsXrepeat[>>shift] </emphasis>.
<itemizedlist>
<listitem> <emphasis>be</emphasis> or <emphasis>le</emphasis>, specifies
big or little endian.
</listitem>
<listitem>
<emphasis>s </emphasis>or <emphasis>u</emphasis>, specifies if
signed (2's complement) or unsigned.
</listitem>
<listitem><emphasis>bits</emphasis>, is the number of valid data
bits.
</listitem>
<listitem><emphasis>storagebits</emphasis>, is the number of bits
(after padding) that it occupies in the buffer.
</listitem>
<listitem>
<emphasis>shift</emphasis>, if specified, is the shift that needs
to be applied prior to masking out unused bits.
</listitem>
<listitem>
<emphasis>repeat</emphasis>, specifies the number of bits/storagebits
repetitions. When the repeat element is 0 or 1, then the repeat
value is omitted.
</listitem>
</itemizedlist>
</listitem>
</itemizedlist>
For example, a driver for a 3-axis accelerometer with 12 bit
resolution where data is stored in two 8-bits registers as
follows:
<programlisting>
7 6 5 4 3 2 1 0
+---+---+---+---+---+---+---+---+
|D3 |D2 |D1 |D0 | X | X | X | X | (LOW byte, address 0x06)
+---+---+---+---+---+---+---+---+
7 6 5 4 3 2 1 0
+---+---+---+---+---+---+---+---+
|D11|D10|D9 |D8 |D7 |D6 |D5 |D4 | (HIGH byte, address 0x07)
+---+---+---+---+---+---+---+---+
</programlisting>
will have the following scan element type for each axis:
<programlisting>
$ cat /sys/bus/iio/devices/iio:device0/scan_elements/in_accel_y_type
le:s12/16>>4
</programlisting>
A user space application will interpret data samples read from the
buffer as two byte little endian signed data, that needs a 4 bits
right shift before masking out the 12 valid bits of data.
</para>
<para>
For implementing buffer support a driver should initialize the following
fields in <type>iio_chan_spec</type> definition:
<programlisting>
struct iio_chan_spec {
/* other members */
int scan_index
struct {
char sign;
u8 realbits;
u8 storagebits;
u8 shift;
u8 repeat;
enum iio_endian endianness;
} scan_type;
};
</programlisting>
The driver implementing the accelerometer described above will
have the following channel definition:
<programlisting>
struct struct iio_chan_spec accel_channels[] = {
{
.type = IIO_ACCEL,
.modified = 1,
.channel2 = IIO_MOD_X,
/* other stuff here */
.scan_index = 0,
.scan_type = {
.sign = 's',
.realbits = 12,
.storagebits = 16,
.shift = 4,
.endianness = IIO_LE,
},
}
/* similar for Y (with channel2 = IIO_MOD_Y, scan_index = 1)
* and Z (with channel2 = IIO_MOD_Z, scan_index = 2) axis
*/
}
</programlisting>
</para>
<para>
Here <emphasis> scan_index </emphasis> defines the order in which
the enabled channels are placed inside the buffer. Channels with a lower
scan_index will be placed before channels with a higher index. Each
channel needs to have a unique scan_index.
</para>
<para>
Setting scan_index to -1 can be used to indicate that the specific
channel does not support buffered capture. In this case no entries will
be created for the channel in the scan_elements directory.
</para>
</sect2>
</sect1>
<sect1 id="iiotrigger"> <title> Industrial I/O triggers </title>
!Finclude/linux/iio/trigger.h iio_trigger
!Edrivers/iio/industrialio-trigger.c
<para>
In many situations it is useful for a driver to be able to
capture data based on some external event (trigger) as opposed
to periodically polling for data. An IIO trigger can be provided
by a device driver that also has an IIO device based on hardware
generated events (e.g. data ready or threshold exceeded) or
provided by a separate driver from an independent interrupt
source (e.g. GPIO line connected to some external system, timer
interrupt or user space writing a specific file in sysfs). A
trigger may initiate data capture for a number of sensors and
also it may be completely unrelated to the sensor itself.
</para>
<sect2 id="iiotrigsysfs"> <title> IIO trigger sysfs interface </title>
There are two locations in sysfs related to triggers:
<itemizedlist>
<listitem><filename>/sys/bus/iio/devices/triggerY</filename>,
this file is created once an IIO trigger is registered with
the IIO core and corresponds to trigger with index Y. Because
triggers can be very different depending on type there are few
standard attributes that we can describe here:
<itemizedlist>
<listitem>
<emphasis>name</emphasis>, trigger name that can be later
used for association with a device.
</listitem>
<listitem>
<emphasis>sampling_frequency</emphasis>, some timer based
triggers use this attribute to specify the frequency for
trigger calls.
</listitem>
</itemizedlist>
</listitem>
<listitem>
<filename>/sys/bus/iio/devices/iio:deviceX/trigger/</filename>, this
directory is created once the device supports a triggered
buffer. We can associate a trigger with our device by writing
the trigger's name in the <filename>current_trigger</filename> file.
</listitem>
</itemizedlist>
</sect2>
<sect2 id="iiotrigattr"> <title> IIO trigger setup</title>
<para>
Let's see a simple example of how to setup a trigger to be used
by a driver.
<programlisting>
struct iio_trigger_ops trigger_ops = {
.set_trigger_state = sample_trigger_state,
.validate_device = sample_validate_device,
}
struct iio_trigger *trig;
/* first, allocate memory for our trigger */
trig = iio_trigger_alloc(dev, "trig-%s-%d", name, idx);
/* setup trigger operations field */
trig->ops = &amp;trigger_ops;
/* now register the trigger with the IIO core */
iio_trigger_register(trig);
</programlisting>
</para>
</sect2>
<sect2 id="iiotrigsetup"> <title> IIO trigger ops</title>
!Finclude/linux/iio/trigger.h iio_trigger_ops
<para>
Notice that a trigger has a set of operations attached:
<itemizedlist>
<listitem>
<function>set_trigger_state</function>, switch the trigger on/off
on demand.
</listitem>
<listitem>
<function>validate_device</function>, function to validate the
device when the current trigger gets changed.
</listitem>
</itemizedlist>
</para>
</sect2>
</sect1>
<sect1 id="iiotriggered_buffer">
<title> Industrial I/O triggered buffers </title>
<para>
Now that we know what buffers and triggers are let's see how they
work together.
</para>
<sect2 id="iiotrigbufsetup"> <title> IIO triggered buffer setup</title>
!Edrivers/iio/buffer/industrialio-triggered-buffer.c
!Finclude/linux/iio/iio.h iio_buffer_setup_ops
<para>
A typical triggered buffer setup looks like this:
<programlisting>
const struct iio_buffer_setup_ops sensor_buffer_setup_ops = {
.preenable = sensor_buffer_preenable,
.postenable = sensor_buffer_postenable,
.postdisable = sensor_buffer_postdisable,
.predisable = sensor_buffer_predisable,
};
irqreturn_t sensor_iio_pollfunc(int irq, void *p)
{
pf->timestamp = iio_get_time_ns((struct indio_dev *)p);
return IRQ_WAKE_THREAD;
}
irqreturn_t sensor_trigger_handler(int irq, void *p)
{
u16 buf[8];
int i = 0;
/* read data for each active channel */
for_each_set_bit(bit, active_scan_mask, masklength)
buf[i++] = sensor_get_data(bit)
iio_push_to_buffers_with_timestamp(indio_dev, buf, timestamp);
iio_trigger_notify_done(trigger);
return IRQ_HANDLED;
}
/* setup triggered buffer, usually in probe function */
iio_triggered_buffer_setup(indio_dev, sensor_iio_polfunc,
sensor_trigger_handler,
sensor_buffer_setup_ops);
</programlisting>
</para>
The important things to notice here are:
<itemizedlist>
<listitem><function> iio_buffer_setup_ops</function>, the buffer setup
functions to be called at predefined points in the buffer configuration
sequence (e.g. before enable, after disable). If not specified, the
IIO core uses the default <type>iio_triggered_buffer_setup_ops</type>.
</listitem>
<listitem><function>sensor_iio_pollfunc</function>, the function that
will be used as top half of poll function. It should do as little
processing as possible, because it runs in interrupt context. The most
common operation is recording of the current timestamp and for this reason
one can use the IIO core defined <function>iio_pollfunc_store_time
</function> function.
</listitem>
<listitem><function>sensor_trigger_handler</function>, the function that
will be used as bottom half of the poll function. This runs in the
context of a kernel thread and all the processing takes place here.
It usually reads data from the device and stores it in the internal
buffer together with the timestamp recorded in the top half.
</listitem>
</itemizedlist>
</sect2>
</sect1>
</chapter>
<chapter id='iioresources'>
<title> Resources </title>
IIO core may change during time so the best documentation to read is the
source code. There are several locations where you should look:
<itemizedlist>
<listitem>
<filename>drivers/iio/</filename>, contains the IIO core plus
and directories for each sensor type (e.g. accel, magnetometer,
etc.)
</listitem>
<listitem>
<filename>include/linux/iio/</filename>, contains the header
files, nice to read for the internal kernel interfaces.
</listitem>
<listitem>
<filename>include/uapi/linux/iio/</filename>, contains files to be
used by user space applications.
</listitem>
<listitem>
<filename>tools/iio/</filename>, contains tools for rapidly
testing buffers, events and device creation.
</listitem>
<listitem>
<filename>drivers/staging/iio/</filename>, contains code for some
drivers or experimental features that are not yet mature enough
to be moved out.
</listitem>
</itemizedlist>
<para>
Besides the code, there are some good online documentation sources:
<itemizedlist>
<listitem>
<ulink url="http://marc.info/?l=linux-iio"> Industrial I/O mailing
list </ulink>
</listitem>
<listitem>
<ulink url="http://wiki.analog.com/software/linux/docs/iio/iio">
Analog Device IIO wiki page </ulink>
</listitem>
<listitem>
<ulink url="https://fosdem.org/2015/schedule/event/iiosdr/">
Using the Linux IIO framework for SDR, Lars-Peter Clausen's
presentation at FOSDEM </ulink>
</listitem>
</itemizedlist>
</para>
</chapter>
</book>
<!--
vim: softtabstop=2:shiftwidth=2:expandtab:textwidth=72
-->

304
Documentation/DocBook/regulator.tmpl
View file

@ -1,304 +0,0 @@
<?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="regulator-api">
<bookinfo>
<title>Voltage and current regulator API</title>
<authorgroup>
<author>
<firstname>Liam</firstname>
<surname>Girdwood</surname>
<affiliation>
<address>
<email>[email protected]</email>
</address>
</affiliation>
</author>
<author>
<firstname>Mark</firstname>
<surname>Brown</surname>
<affiliation>
<orgname>Wolfson Microelectronics</orgname>
<address>
<email>[email protected]</email>
</address>
</affiliation>
</author>
</authorgroup>
<copyright>
<year>2007-2008</year>
<holder>Wolfson Microelectronics</holder>
</copyright>
<copyright>
<year>2008</year>
<holder>Liam Girdwood</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 version 2 as published by the Free Software Foundation.
</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>
This framework is designed to provide a standard kernel
interface to control voltage and current regulators.
</para>
<para>
The intention is to allow systems to dynamically control
regulator power output in order to save power and prolong
battery life. This applies to both voltage regulators (where
voltage output is controllable) and current sinks (where current
limit is controllable).
</para>
<para>
Note that additional (and currently more complete) documentation
is available in the Linux kernel source under
<filename>Documentation/power/regulator</filename>.
</para>
<sect1 id="glossary">
<title>Glossary</title>
<para>
The regulator API uses a number of terms which may not be
familiar:
</para>
<glossary>
<glossentry>
<glossterm>Regulator</glossterm>
<glossdef>
<para>
Electronic device that supplies power to other devices. Most
regulators can enable and disable their output and some can also
control their output voltage or current.
</para>
</glossdef>
</glossentry>
<glossentry>
<glossterm>Consumer</glossterm>
<glossdef>
<para>
Electronic device which consumes power provided by a regulator.
These may either be static, requiring only a fixed supply, or
dynamic, requiring active management of the regulator at
runtime.
</para>
</glossdef>
</glossentry>
<glossentry>
<glossterm>Power Domain</glossterm>
<glossdef>
<para>
The electronic circuit supplied by a given regulator, including
the regulator and all consumer devices. The configuration of
the regulator is shared between all the components in the
circuit.
</para>
</glossdef>
</glossentry>
<glossentry>
<glossterm>Power Management Integrated Circuit</glossterm>
<acronym>PMIC</acronym>
<glossdef>
<para>
An IC which contains numerous regulators and often also other
subsystems. In an embedded system the primary PMIC is often
equivalent to a combination of the PSU and southbridge in a
desktop system.
</para>
</glossdef>
</glossentry>
</glossary>
</sect1>
</chapter>
<chapter id="consumer">
<title>Consumer driver interface</title>
<para>
This offers a similar API to the kernel clock framework.
Consumer drivers use <link
linkend='API-regulator-get'>get</link> and <link
linkend='API-regulator-put'>put</link> operations to acquire and
release regulators. Functions are
provided to <link linkend='API-regulator-enable'>enable</link>
and <link linkend='API-regulator-disable'>disable</link> the
regulator and to get and set the runtime parameters of the
regulator.
</para>
<para>
When requesting regulators consumers use symbolic names for their
supplies, such as "Vcc", which are mapped into actual regulator
devices by the machine interface.
</para>
<para>
A stub version of this API is provided when the regulator
framework is not in use in order to minimise the need to use
ifdefs.
</para>
<sect1 id="consumer-enable">
<title>Enabling and disabling</title>
<para>
The regulator API provides reference counted enabling and
disabling of regulators. Consumer devices use the <function><link
linkend='API-regulator-enable'>regulator_enable</link></function>
and <function><link
linkend='API-regulator-disable'>regulator_disable</link>
</function> functions to enable and disable regulators. Calls
to the two functions must be balanced.
</para>
<para>
Note that since multiple consumers may be using a regulator and
machine constraints may not allow the regulator to be disabled
there is no guarantee that calling
<function>regulator_disable</function> will actually cause the
supply provided by the regulator to be disabled. Consumer
drivers should assume that the regulator may be enabled at all
times.
</para>
</sect1>
<sect1 id="consumer-config">
<title>Configuration</title>
<para>
Some consumer devices may need to be able to dynamically
configure their supplies. For example, MMC drivers may need to
select the correct operating voltage for their cards. This may
be done while the regulator is enabled or disabled.
</para>
<para>
The <function><link
linkend='API-regulator-set-voltage'>regulator_set_voltage</link>
</function> and <function><link
linkend='API-regulator-set-current-limit'
>regulator_set_current_limit</link>
</function> functions provide the primary interface for this.
Both take ranges of voltages and currents, supporting drivers
that do not require a specific value (eg, CPU frequency scaling
normally permits the CPU to use a wider range of supply
voltages at lower frequencies but does not require that the
supply voltage be lowered). Where an exact value is required
both minimum and maximum values should be identical.
</para>
</sect1>
<sect1 id="consumer-callback">
<title>Callbacks</title>
<para>
Callbacks may also be <link
linkend='API-regulator-register-notifier'>registered</link>
for events such as regulation failures.
</para>
</sect1>
</chapter>
<chapter id="driver">
<title>Regulator driver interface</title>
<para>
Drivers for regulator chips <link
linkend='API-regulator-register'>register</link> the regulators
with the regulator core, providing operations structures to the
core. A <link
linkend='API-regulator-notifier-call-chain'>notifier</link> interface
allows error conditions to be reported to the core.
</para>
<para>
Registration should be triggered by explicit setup done by the
platform, supplying a <link
linkend='API-struct-regulator-init-data'>struct
regulator_init_data</link> for the regulator containing
<link linkend='machine-constraint'>constraint</link> and
<link linkend='machine-supply'>supply</link> information.
</para>
</chapter>
<chapter id="machine">
<title>Machine interface</title>
<para>
This interface provides a way to define how regulators are
connected to consumers on a given system and what the valid
operating parameters are for the system.
</para>
<sect1 id="machine-supply">
<title>Supplies</title>
<para>
Regulator supplies are specified using <link
linkend='API-struct-regulator-consumer-supply'>struct
regulator_consumer_supply</link>. This is done at
<link linkend='driver'>driver registration
time</link> as part of the machine constraints.
</para>
</sect1>
<sect1 id="machine-constraint">
<title>Constraints</title>
<para>
As well as defining the connections the machine interface
also provides constraints defining the operations that
clients are allowed to perform and the parameters that may be
set. This is required since generally regulator devices will
offer more flexibility than it is safe to use on a given
system, for example supporting higher supply voltages than the
consumers are rated for.
</para>
<para>
This is done at <link linkend='driver'>driver
registration time</link> by providing a <link
linkend='API-struct-regulation-constraints'>struct
regulation_constraints</link>.
</para>
<para>
The constraints may also specify an initial configuration for the
regulator in the constraints, which is particularly useful for
use with static consumers.
</para>
</sect1>
</chapter>
<chapter id="api">
<title>API reference</title>
<para>
Due to limitations of the kernel documentation framework and the
existing layout of the source code the entire regulator API is
documented here.
</para>
!Iinclude/linux/regulator/consumer.h
!Iinclude/linux/regulator/machine.h
!Iinclude/linux/regulator/driver.h
!Edrivers/regulator/core.c
</chapter>
</book>