diff options
Diffstat (limited to 'Documentation/DocBook')
| -rw-r--r-- | Documentation/DocBook/Makefile | 10 | ||||
| -rw-r--r-- | Documentation/DocBook/deviceiobook.tmpl | 3 | ||||
| -rw-r--r-- | Documentation/DocBook/kernel-api.tmpl | 88 | ||||
| -rw-r--r-- | Documentation/DocBook/kernel-locking.tmpl | 2 | ||||
| -rw-r--r-- | Documentation/DocBook/libata.tmpl | 5 | ||||
| -rw-r--r-- | Documentation/DocBook/procfs-guide.tmpl | 82 | ||||
| -rw-r--r-- | Documentation/DocBook/uio-howto.tmpl | 607 |
7 files changed, 764 insertions, 33 deletions
diff --git a/Documentation/DocBook/Makefile b/Documentation/DocBook/Makefile index 6fd1646d3204..08687e45e19d 100644 --- a/Documentation/DocBook/Makefile +++ b/Documentation/DocBook/Makefile @@ -15,11 +15,11 @@ DOCBOOKS := wanbook.xml z8530book.xml mcabook.xml videobook.xml \ ### # The build process is as follows (targets): -# (xmldocs) -# file.tmpl --> file.xml +--> file.ps (psdocs) -# +--> file.pdf (pdfdocs) -# +--> DIR=file (htmldocs) -# +--> man/ (mandocs) +# (xmldocs) [by docproc] +# file.tmpl --> file.xml +--> file.ps (psdocs) [by db2ps or xmlto] +# +--> file.pdf (pdfdocs) [by db2pdf or xmlto] +# +--> DIR=file (htmldocs) [by xmlto] +# +--> man/ (mandocs) [by xmlto] # for PDF and PS output you can choose between xmlto and docbook-utils tools diff --git a/Documentation/DocBook/deviceiobook.tmpl b/Documentation/DocBook/deviceiobook.tmpl index 90ed23df1f68..c917de681ccd 100644 --- a/Documentation/DocBook/deviceiobook.tmpl +++ b/Documentation/DocBook/deviceiobook.tmpl @@ -316,7 +316,8 @@ CPU B: spin_unlock_irqrestore(&dev_lock, flags) <chapter id="pubfunctions"> <title>Public Functions Provided</title> -!Einclude/asm-i386/io.h +!Iinclude/asm-i386/io.h +!Elib/iomap.c </chapter> </book> diff --git a/Documentation/DocBook/kernel-api.tmpl b/Documentation/DocBook/kernel-api.tmpl index 38f88b6ae405..b886f52a9aac 100644 --- a/Documentation/DocBook/kernel-api.tmpl +++ b/Documentation/DocBook/kernel-api.tmpl @@ -139,8 +139,10 @@ X!Ilib/string.c !Elib/cmdline.c </sect1> - <sect1><title>CRC Functions</title> + <sect1 id="crc"><title>CRC Functions</title> +!Elib/crc7.c !Elib/crc16.c +!Elib/crc-itu-t.c !Elib/crc32.c !Elib/crc-ccitt.c </sect1> @@ -157,7 +159,6 @@ X!Ilib/string.c !Earch/i386/lib/usercopy.c </sect1> <sect1><title>More Memory Management Functions</title> -!Iinclude/linux/rmap.h !Emm/readahead.c !Emm/filemap.c !Emm/memory.c @@ -379,7 +380,6 @@ X!Edrivers/base/interface.c !Edrivers/base/bus.c </sect1> <sect1><title>Device Drivers Power Management</title> -!Edrivers/base/power/main.c !Edrivers/base/power/resume.c !Edrivers/base/power/suspend.c </sect1> @@ -397,15 +397,19 @@ X!Edrivers/acpi/pci_bind.c --> </sect1> <sect1><title>Device drivers PnP support</title> -!Edrivers/pnp/core.c +!Idrivers/pnp/core.c <!-- No correct structured comments X!Edrivers/pnp/system.c --> !Edrivers/pnp/card.c -!Edrivers/pnp/driver.c +!Idrivers/pnp/driver.c !Edrivers/pnp/manager.c !Edrivers/pnp/support.c </sect1> + <sect1><title>Userspace IO devices</title> +!Edrivers/uio/uio.c +!Iinclude/linux/uio_driver.h + </sect1> </chapter> <chapter id="blkdev"> @@ -643,4 +647,78 @@ X!Idrivers/video/console/fonts.c !Edrivers/spi/spi.c </chapter> + <chapter id="i2c"> + <title>I<superscript>2</superscript>C and SMBus Subsystem</title> + + <para> + I<superscript>2</superscript>C (or without fancy typography, "I2C") + is an acronym for the "Inter-IC" bus, a simple bus protocol which is + widely used where low data rate communications suffice. + Since it's also a licensed trademark, some vendors use another + name (such as "Two-Wire Interface", TWI) for the same bus. + I2C only needs two signals (SCL for clock, SDA for data), conserving + board real estate and minimizing signal quality issues. + Most I2C devices use seven bit addresses, and bus speeds of up + to 400 kHz; there's a high speed extension (3.4 MHz) that's not yet + found wide use. + I2C is a multi-master bus; open drain signaling is used to + arbitrate between masters, as well as to handshake and to + synchronize clocks from slower clients. + </para> + + <para> + The Linux I2C programming interfaces support only the master + side of bus interactions, not the slave side. + The programming interface is structured around two kinds of driver, + and two kinds of device. + An I2C "Adapter Driver" abstracts the controller hardware; it binds + to a physical device (perhaps a PCI device or platform_device) and + exposes a <structname>struct i2c_adapter</structname> representing + each I2C bus segment it manages. + On each I2C bus segment will be I2C devices represented by a + <structname>struct i2c_client</structname>. Those devices will + be bound to a <structname>struct i2c_driver</structname>, + which should follow the standard Linux driver model. + (At this writing, a legacy model is more widely used.) + There are functions to perform various I2C protocol operations; at + this writing all such functions are usable only from task context. + </para> + + <para> + The System Management Bus (SMBus) is a sibling protocol. Most SMBus + systems are also I2C conformant. The electrical constraints are + tighter for SMBus, and it standardizes particular protocol messages + and idioms. Controllers that support I2C can also support most + SMBus operations, but SMBus controllers don't support all the protocol + options that an I2C controller will. + There are functions to perform various SMBus protocol operations, + either using I2C primitives or by issuing SMBus commands to + i2c_adapter devices which don't support those I2C operations. + </para> + +!Iinclude/linux/i2c.h +!Fdrivers/i2c/i2c-boardinfo.c i2c_register_board_info +!Edrivers/i2c/i2c-core.c + </chapter> + + <chapter id="splice"> + <title>splice API</title> + <para> + splice is a method for moving blocks of data around inside the + kernel, without continually transferring them between the kernel + and user space. + </para> +!Ffs/splice.c + </chapter> + + <chapter id="pipes"> + <title>pipes API</title> + <para> + Pipe interfaces are all for in-kernel (builtin image) use. + They are not exported for use by modules. + </para> +!Iinclude/linux/pipe_fs_i.h +!Ffs/pipe.c + </chapter> + </book> diff --git a/Documentation/DocBook/kernel-locking.tmpl b/Documentation/DocBook/kernel-locking.tmpl index 0a441f73261a..01825ee7db64 100644 --- a/Documentation/DocBook/kernel-locking.tmpl +++ b/Documentation/DocBook/kernel-locking.tmpl @@ -219,7 +219,7 @@ </para> <sect1 id="lock-intro"> - <title>Two Main Types of Kernel Locks: Spinlocks and Semaphores</title> + <title>Three Main Types of Kernel Locks: Spinlocks, Mutexes and Semaphores</title> <para> There are three main types of kernel locks. The fundamental type diff --git a/Documentation/DocBook/libata.tmpl b/Documentation/DocBook/libata.tmpl index e2e24b4778d4..ba9975771503 100644 --- a/Documentation/DocBook/libata.tmpl +++ b/Documentation/DocBook/libata.tmpl @@ -456,8 +456,9 @@ void (*irq_clear) (struct ata_port *); <sect2><title>SATA phy read/write</title> <programlisting> -u32 (*scr_read) (struct ata_port *ap, unsigned int sc_reg); -void (*scr_write) (struct ata_port *ap, unsigned int sc_reg, +int (*scr_read) (struct ata_port *ap, unsigned int sc_reg, + u32 *val); +int (*scr_write) (struct ata_port *ap, unsigned int sc_reg, u32 val); </programlisting> diff --git a/Documentation/DocBook/procfs-guide.tmpl b/Documentation/DocBook/procfs-guide.tmpl index 45cad23efefa..2de84dc195a8 100644 --- a/Documentation/DocBook/procfs-guide.tmpl +++ b/Documentation/DocBook/procfs-guide.tmpl @@ -352,49 +352,93 @@ entry->write_proc = write_proc_foo; <funcsynopsis> <funcprototype> <funcdef>int <function>read_func</function></funcdef> - <paramdef>char* <parameter>page</parameter></paramdef> + <paramdef>char* <parameter>buffer</parameter></paramdef> <paramdef>char** <parameter>start</parameter></paramdef> <paramdef>off_t <parameter>off</parameter></paramdef> <paramdef>int <parameter>count</parameter></paramdef> - <paramdef>int* <parameter>eof</parameter></paramdef> + <paramdef>int* <parameter>peof</parameter></paramdef> <paramdef>void* <parameter>data</parameter></paramdef> </funcprototype> </funcsynopsis> <para> The read function should write its information into the - <parameter>page</parameter>. For proper use, the function - should start writing at an offset of - <parameter>off</parameter> in <parameter>page</parameter> and - write at most <parameter>count</parameter> bytes, but because - most read functions are quite simple and only return a small - amount of information, these two parameters are usually - ignored (it breaks pagers like <literal>more</literal> and - <literal>less</literal>, but <literal>cat</literal> still - works). + <parameter>buffer</parameter>, which will be exactly + <literal>PAGE_SIZE</literal> bytes long. </para> <para> - If the <parameter>off</parameter> and - <parameter>count</parameter> parameters are properly used, - <parameter>eof</parameter> should be used to signal that the + The parameter + <parameter>peof</parameter> should be used to signal that the end of the file has been reached by writing <literal>1</literal> to the memory location - <parameter>eof</parameter> points to. + <parameter>peof</parameter> points to. </para> <para> - The parameter <parameter>start</parameter> doesn't seem to be - used anywhere in the kernel. The <parameter>data</parameter> + The <parameter>data</parameter> parameter can be used to create a single call back function for several files, see <xref linkend="usingdata"/>. </para> <para> - The <function>read_func</function> function must return the - number of bytes written into the <parameter>page</parameter>. + The rest of the parameters and the return value are described + by a comment in <filename>fs/proc/generic.c</filename> as follows: </para> + <blockquote> + <para> + You have three ways to return data: + </para> + <orderedlist> + <listitem> + <para> + Leave <literal>*start = NULL</literal>. (This is the default.) + Put the data of the requested offset at that + offset within the buffer. Return the number (<literal>n</literal>) + of bytes there are from the beginning of the + buffer up to the last byte of data. If the + number of supplied bytes (<literal>= n - offset</literal>) is + greater than zero and you didn't signal eof + and the reader is prepared to take more data + you will be called again with the requested + offset advanced by the number of bytes + absorbed. This interface is useful for files + no larger than the buffer. + </para> + </listitem> + <listitem> + <para> + Set <literal>*start</literal> to an unsigned long value less than + the buffer address but greater than zero. + Put the data of the requested offset at the + beginning of the buffer. Return the number of + bytes of data placed there. If this number is + greater than zero and you didn't signal eof + and the reader is prepared to take more data + you will be called again with the requested + offset advanced by <literal>*start</literal>. This interface is + useful when you have a large file consisting + of a series of blocks which you want to count + and return as wholes. + (Hack by Paul.Russell@rustcorp.com.au) + </para> + </listitem> + <listitem> + <para> + Set <literal>*start</literal> to an address within the buffer. + Put the data of the requested offset at <literal>*start</literal>. + Return the number of bytes of data placed there. + If this number is greater than zero and you + didn't signal eof and the reader is prepared to + take more data you will be called again with the + requested offset advanced by the number of bytes + absorbed. + </para> + </listitem> + </orderedlist> + </blockquote> + <para> <xref linkend="example"/> shows how to use a read call back function. diff --git a/Documentation/DocBook/uio-howto.tmpl b/Documentation/DocBook/uio-howto.tmpl new file mode 100644 index 000000000000..c119484258b8 --- /dev/null +++ b/Documentation/DocBook/uio-howto.tmpl @@ -0,0 +1,607 @@ +<?xml version="1.0" encoding="UTF-8"?> +<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" +"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd" []> + +<book id="index"> +<bookinfo> +<title>The Userspace I/O HOWTO</title> + +<author> + <firstname>Hans-Jürgen</firstname> + <surname>Koch</surname> + <authorblurb><para>Linux developer, Linutronix</para></authorblurb> + <affiliation> + <orgname> + <ulink url="http://www.linutronix.de">Linutronix</ulink> + </orgname> + + <address> + <email>hjk@linutronix.de</email> + </address> + </affiliation> +</author> + +<pubdate>2006-12-11</pubdate> + +<abstract> + <para>This HOWTO describes concept and usage of Linux kernel's + Userspace I/O system.</para> +</abstract> + +<revhistory> + <revision> + <revnumber>0.3</revnumber> + <date>2007-04-29</date> + <authorinitials>hjk</authorinitials> + <revremark>Added section about userspace drivers.</revremark> + </revision> + <revision> + <revnumber>0.2</revnumber> + <date>2007-02-13</date> + <authorinitials>hjk</authorinitials> + <revremark>Update after multiple mappings were added.</revremark> + </revision> + <revision> + <revnumber>0.1</revnumber> + <date>2006-12-11</date> + <authorinitials>hjk</authorinitials> + <revremark>First draft.</revremark> + </revision> +</revhistory> +</bookinfo> + +<chapter id="aboutthisdoc"> +<?dbhtml filename="about.html"?> +<title>About this document</title> + +<sect1 id="copyright"> +<?dbhtml filename="copyright.html"?> +<title>Copyright and License</title> +<para> + Copyright (c) 2006 by Hans-Jürgen Koch.</para> +<para> +This documentation is Free Software licensed under the terms of the +GPL version 2. +</para> +</sect1> + +<sect1 id="translations"> +<?dbhtml filename="translations.html"?> +<title>Translations</title> + +<para>If you know of any translations for this document, or you are +interested in translating it, please email me +<email>hjk@linutronix.de</email>. +</para> +</sect1> + +<sect1 id="preface"> +<title>Preface</title> + <para> + For many types of devices, creating a Linux kernel driver is + overkill. All that is really needed is some way to handle an + interrupt and provide access to the memory space of the + device. The logic of controlling the device does not + necessarily have to be within the kernel, as the device does + not need to take advantage of any of other resources that the + kernel provides. One such common class of devices that are + like this are for industrial I/O cards. + </para> + <para> + To address this situation, the userspace I/O system (UIO) was + designed. For typical industrial I/O cards, only a very small + kernel module is needed. The main part of the driver will run in + user space. This simplifies development and reduces the risk of + serious bugs within a kernel module. + </para> +</sect1> + +<sect1 id="thanks"> +<title>Acknowledgments</title> + <para>I'd like to thank Thomas Gleixner and Benedikt Spranger of + Linutronix, who have not only written most of the UIO code, but also + helped greatly writing this HOWTO by giving me all kinds of background + information.</para> +</sect1> + +<sect1 id="feedback"> +<title>Feedback</title> + <para>Find something wrong with this document? (Or perhaps something + right?) I would love to hear from you. Please email me at + <email>hjk@linutronix.de</email>.</para> +</sect1> +</chapter> + +<chapter id="about"> +<?dbhtml filename="about.html"?> +<title>About UIO</title> + +<para>If you use UIO for your card's driver, here's what you get:</para> + +<itemizedlist> +<listitem> + <para>only one small kernel module to write and maintain.</para> +</listitem> +<listitem> + <para>develop the main part of your driver in user space, + with all the tools and libraries you're used to.</para> +</listitem> +<listitem> + <para>bugs in your driver won't crash the kernel.</para> +</listitem> +<listitem> + <para>updates of your driver can take place without recompiling + the kernel.</para> +</listitem> +</itemizedlist> + +<sect1 id="how_uio_works"> +<title>How UIO works</title> + <para> + Each UIO device is accessed through a device file and several + sysfs attribute files. The device file will be called + <filename>/dev/uio0</filename> for the first device, and + <filename>/dev/uio1</filename>, <filename>/dev/uio2</filename> + and so on for subsequent devices. + </para> + + <para><filename>/dev/uioX</filename> is used to access the + address space of the card. Just use + <function>mmap()</function> to access registers or RAM + locations of your card. + </para> + + <para> + Interrupts are handled by reading from + <filename>/dev/uioX</filename>. A blocking + <function>read()</function> from + <filename>/dev/uioX</filename> will return as soon as an + interrupt occurs. You can also use + <function>select()</function> on + <filename>/dev/uioX</filename> to wait for an interrupt. The + integer value read from <filename>/dev/uioX</filename> + represents the total interrupt count. You can use this number + to figure out if you missed some interrupts. + </para> + + <para> + To handle interrupts properly, your custom kernel module can + provide its own interrupt handler. It will automatically be + called by the built-in handler. + </para> + + <para> + For cards that don't generate interrupts but need to be + polled, there is the possibility to set up a timer that + triggers the interrupt handler at configurable time intervals. + See <filename>drivers/uio/uio_dummy.c</filename> for an + example of this technique. + </para> + + <para> + Each driver provides attributes that are used to read or write + variables. These attributes are accessible through sysfs + files. A custom kernel driver module can add its own + attributes to the device owned by the uio driver, but not added + to the UIO device itself at this time. This might change in the + future if it would be found to be useful. + </para> + + <para> + The following standard attributes are provided by the UIO + framework: + </para> +<itemizedlist> +<listitem> + <para> + <filename>name</filename>: The name of your device. It is + recommended to use the name of your kernel module for this. + </para> +</listitem> +<listitem> + <para> + <filename>version</filename>: A version string defined by your + driver. This allows the user space part of your driver to deal + with different versions of the kernel module. + </para> +</listitem> +<listitem> + <para> + <filename>event</filename>: The total number of interrupts + handled by the driver since the last time the device node was + read. + </para> +</listitem> +</itemizedlist> +<para> + These attributes appear under the + <filename>/sys/class/uio/uioX</filename> directory. Please + note that this directory might be a symlink, and not a real + directory. Any userspace code that accesses it must be able + to handle this. +</para> +<para> + Each UIO device can make one or more memory regions available for + memory mapping. This is necessary because some industrial I/O cards + require access to more than one PCI memory region in a driver. +</para> +<para> + Each mapping has its own directory in sysfs, the first mapping + appears as <filename>/sys/class/uio/uioX/maps/map0/</filename>. + Subsequent mappings create directories <filename>map1/</filename>, + <filename>map2/</filename>, and so on. These directories will only + appear if the size of the mapping is not 0. +</para> +<para> + Each <filename>mapX/</filename> directory contains two read-only files + that show start address and size of the memory: +</para> +<itemizedlist> +<listitem> + <para> + <filename>addr</filename>: The address of memory that can be mapped. + </para> +</listitem> +<listitem> + <para> + <filename>size</filename>: The size, in bytes, of the memory + pointed to by addr. + </para> +</listitem> +</itemizedlist> + +<para> + From userspace, the different mappings are distinguished by adjusting + the <varname>offset</varname> parameter of the + <function>mmap()</function> call. To map the memory of mapping N, you + have to use N times the page size as your offset: +</para> +<programlisting format="linespecific"> +offset = N * getpagesize(); +</programlisting> + +</sect1> +</chapter> + +<chapter id="using-uio_dummy" xreflabel="Using uio_dummy"> +<?dbhtml filename="using-uio_dummy.html"?> +<title>Using uio_dummy</title> + <para> + Well, there is no real use for uio_dummy. Its only purpose is + to test most parts of the UIO system (everything except + hardware interrupts), and to serve as an example for the + kernel module that you will have to write yourself. + </para> + +<sect1 id="what_uio_dummy_does"> +<title>What uio_dummy does</title> + <para> + The kernel module <filename>uio_dummy.ko</filename> creates a + device that uses a timer to generate periodic interrupts. The + interrupt handler does nothing but increment a counter. The + driver adds two custom attributes, <varname>count</varname> + and <varname>freq</varname>, that appear under + <filename>/sys/devices/platform/uio_dummy/</filename>. + </para> + + <para> + The attribute <varname>count</varname> can be read and + written. The associated file + <filename>/sys/devices/platform/uio_dummy/count</filename> + appears as a normal text file and contains the total number of + timer interrupts. If you look at it (e.g. using + <function>cat</function>), you'll notice it is slowly counting + up. + </para> + + <para> + The attribute <varname>freq</varname> can be read and written. + The content of + <filename>/sys/devices/platform/uio_dummy/freq</filename> + represents the number of system timer ticks between two timer + interrupts. The default value of <varname>freq</varname> is + the value of the kernel variable <varname>HZ</varname>, which + gives you an interval of one second. Lower values will + increase the frequency. Try the following: + </para> +<programlisting format="linespecific"> +cd /sys/devices/platform/uio_dummy/ +echo 100 > freq +</programlisting> + <para> + Use <function>cat count</function> to see how the interrupt + frequency changes. + </para> +</sect1> +</chapter> + +<chapter id="custom_kernel_module" xreflabel="Writing your own kernel module"> +<?dbhtml filename="custom_kernel_module.html"?> +<title>Writing your own kernel module</title> + <para> + Please have a look at <filename>uio_dummy.c</filename> as an + example. The following paragraphs explain the different + sections of this file. + </para> + +<sect1 id="uio_info"> +<title>struct uio_info</title> + <para> + This structure tells the framework the details of your driver, + Some of the members are required, others are optional. + </para> + +<itemizedlist> +<listitem><para> +<varname>char *name</varname>: Required. The name of your driver as +it will appear in sysfs. I recommend using the name of your module for this. +</para></listitem> + +<listitem><para> +<varname>char *version</varname>: Required. This string appears in +<filename>/sys/class/uio/uioX/version</filename>. +</para></listitem> + +<listitem><para> +<varname>struct uio_mem mem[ MAX_UIO_MAPS ]</varname>: Required if you +have memory that can be mapped with <function>mmap()</function>. For each +mapping you need to fill one of the <varname>uio_mem</varname> structures. +See the description below for details. +</para></listitem> + +<listitem><para> +<varname>long irq</varname>: Required. If your hardware generates an +interrupt, it's your modules task to determine the irq number during +initialization. If you don't have a hardware generated interrupt but +want to trigger the interrupt handler in some other way, set +<varname>irq</varname> to <varname>UIO_IRQ_CUSTOM</varname>. The +uio_dummy module does this as it triggers the event mechanism in a timer +routine. If you had no interrupt at all, you could set +<varname>irq</varname> to <varname>UIO_IRQ_NONE</varname>, though this +rarely makes sense. +</para></listitem> + +<listitem><para> +<varname>unsigned long irq_flags</varname>: Required if you've set +<varname>irq</varname> to a hardware interrupt number. The flags given +here will be used in the call to <function>request_irq()</function>. +</para></listitem> + +<listitem><para> +<varname>int (*mmap)(struct uio_info *info, struct vm_area_struct +*vma)</varname>: Optional. If you need a special +<function>mmap()</function> function, you can set it here. If this +pointer is not NULL, your <function>mmap()</function> will be called +instead of the built-in one. +</para></listitem> + +<listitem><para> +<varname>int (*open)(struct uio_info *info, struct inode *inode) +</varname>: Optional. You might want to have your own +<function>open()</function>, e.g. to enable interrupts only when your +device is actually used. +</para></listitem> + +<listitem><para> +<varname>int (*release)(struct uio_info *info, struct inode *inode) +</varname>: Optional. If you define your own +<function>open()</function>, you will probably also want a custom +<function>release()</function> function. +</para></listitem> +</itemizedlist> + +<para> +Usually, your device will have one or more memory regions that can be mapped +to user space. For each region, you have to set up a +<varname>struct uio_mem</varname> in the <varname>mem[]</varname> array. +Here's a description of the fields of <varname>struct uio_mem</varname>: +</para> + +<itemizedlist> +<listitem><para> +<varname>int memtype</varname>: Required if the mapping is used. Set this to +<varname>UIO_MEM_PHYS</varname> if you you have physical memory on your +card to be mapped. Use <varname>UIO_MEM_LOGICAL</varname> for logical +memory (e.g. allocated with <function>kmalloc()</function>). There's also +<varname>UIO_MEM_VIRTUAL</varname> for virtual memory. +</para></listitem> + +<listitem><para> +<varname>unsigned long addr</varname>: Required if the mapping is used. +Fill in the address of your memory block. This address is the one that +appears in sysfs. +</para></listitem> + +<listitem><para> +<varname>unsigned long size</varname>: Fill in the size of the +memory block that <varname>addr</varname> points to. If <varname>size</varname> +is zero, the mapping is considered unused. Note that you +<emphasis>must</emphasis> initialize <varname>size</varname> with zero for +all unused mappings. +</para></listitem> + +<listitem><para> +<varname>void *internal_addr</varname>: If you have to access this memory +region from within your kernel module, you will want to map it internally by +using something like <function>ioremap()</function>. Addresses +returned by this function cannot be mapped to user space, so you must not +store it in <varname>addr</varname>. Use <varname>internal_addr</varname> +instead to remember such an address. +</para></listitem> +</itemizedlist> + +<para> +Please do not touch the <varname>kobj</varname> element of +<varname>struct uio_mem</varname>! It is used by the UIO framework +to set up sysfs files for this mapping. Simply leave it alone. +</para> +</sect1> + +<sect1 id="adding_irq_handler"> +<title>Adding an interrupt handler</title> + <para> + What you need to do in your interrupt handler depends on your + hardware and on how you want to handle it. You should try to + keep the amount of code in your kernel interrupt handler low. + If your hardware requires no action that you + <emphasis>have</emphasis> to perform after each interrupt, + then your handler can be empty.</para> <para>If, on the other + hand, your hardware <emphasis>needs</emphasis> some action to + be performed after each interrupt, then you + <emphasis>must</emphasis> do it in your kernel module. Note + that you cannot rely on the userspace part of your driver. Your + userspace program can terminate at any time, possibly leaving + your hardware in a state where proper interrupt handling is + still required. + </para> + + <para> + There might also be applications where you want to read data + from your hardware at each interrupt and buffer it in a piece + of kernel memory you've allocated for that purpose. With this + technique you could avoid loss of data if your userspace + program misses an interrupt. + </para> + + <para> + A note on shared interrupts: Your driver should support + interrupt sharing whenever this is possible. It is possible if + and only if your driver can detect whether your hardware has + triggered the interrupt or not. This is usually done by looking + at an interrupt status register. If your driver sees that the + IRQ bit is actually set, it will perform its actions, and the + handler returns IRQ_HANDLED. If the driver detects that it was + not your hardware that caused the interrupt, it will do nothing + and return IRQ_NONE, allowing the kernel to call the next + possible interrupt handler. + </para> + + <para> + If you decide not to support shared interrupts, your card + won't work in computers with no free interrupts. As this + frequently happens on the PC platform, you can save yourself a + lot of trouble by supporting interrupt sharing. + </para> +</sect1> + +</chapter> + +<chapter id="userspace_driver" xreflabel="Writing a driver in user space"> +<?dbhtml filename="userspace_driver.html"?> +<title>Writing a driver in userspace</title> + <para> + Once you have a working kernel module for your hardware, you can + write the userspace part of your driver. You don't need any special + libraries, your driver can be written in any reasonable language, + you can use floating point numbers and so on. In short, you can + use all the tools and libraries you'd normally use for writing a + userspace application. + </para> + +<sect1 id="getting_uio_information"> +<title>Getting information about your UIO device</title> + <para> + Information about all UIO devices is available in sysfs. The + first thing you should do in your driver is check + <varname>name</varname> and <varname>version</varname> to + make sure your talking to the right device and that its kernel + driver has the version you expect. + </para> + <para> + You should also make sure that the memory mapping you need + exists and has the size you expect. + </para> + <para> + There is a tool called <varname>lsuio</varname> that lists + UIO devices and their attributes. It is available here: + </para> + <para> + <ulink url="http://www.osadl.org/projects/downloads/UIO/user/"> + http://www.osadl.org/projects/downloads/UIO/user/</ulink> + </para> + <para> + With <varname>lsuio</varname> you can quickly check if your + kernel module is loaded and which attributes it exports. + Have a look at the manpage for details. + </para> + <para> + The source code of <varname>lsuio</varname> can serve as an + example for getting information about an UIO device. + The file <filename>uio_helper.c</filename> contains a lot of + functions you could use in your userspace driver code. + </para> +</sect1> + +<sect1 id="mmap_device_memory"> +<title>mmap() device memory</title> + <para> + After you made sure you've got the right device with the + memory mappings you need, all you have to do is to call + <function>mmap()</function> to map the device's memory + to userspace. + </para> + <para> + The parameter <varname>offset</varname> of the + <function>mmap()</function> call has a special meaning + for UIO devices: It is used to select which mapping of + your device you want to map. To map the memory of + mapping N, you have to use N times the page size as + your offset: + </para> +<programlisting format="linespecific"> + offset = N * getpagesize(); +</programlisting> + <para> + N starts from zero, so if you've got only one memory + range to map, set <varname>offset = 0</varname>. + A drawback of this technique is that memory is always + mapped beginning with its start address. + </para> +</sect1> + +<sect1 id="wait_for_interrupts"> +<title>Waiting for interrupts</title> + <para> + After you successfully mapped your devices memory, you + can access it like an ordinary array. Usually, you will + perform some initialization. After that, your hardware + starts working and will generate an interrupt as soon + as it's finished, has some data available, or needs your + attention because an error occured. + </para> + <para> + <filename>/dev/uioX</filename> is a read-only file. A + <function>read()</function> will always block until an + interrupt occurs. There is only one legal value for the + <varname>count</varname> parameter of + <function>read()</function>, and that is the size of a + signed 32 bit integer (4). Any other value for + <varname>count</varname> causes <function>read()</function> + to fail. The signed 32 bit integer read is the interrupt + count of your device. If the value is one more than the value + you read the last time, everything is OK. If the difference + is greater than one, you missed interrupts. + </para> + <para> + You can also use <function>select()</function> on + <filename>/dev/uioX</filename>. + </para> +</sect1> + +</chapter> + +<appendix id="app1"> +<title>Further information</title> +<itemizedlist> + <listitem><para> + <ulink url="http://www.osadl.org"> + OSADL homepage.</ulink> + </para></listitem> + <listitem><para> + <ulink url="http://www.linutronix.de"> + Linutronix homepage.</ulink> + </para></listitem> +</itemizedlist> +</appendix> + +</book> |