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Hans J. Koche3e0a282006-12-11 16:59:59 +01001<?xml version="1.0" encoding="UTF-8"?>
2<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
3"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd" []>
4
5<book id="index">
6<bookinfo>
7<title>The Userspace I/O HOWTO</title>
8
9<author>
10 <firstname>Hans-Jürgen</firstname>
11 <surname>Koch</surname>
12 <authorblurb><para>Linux developer, Linutronix</para></authorblurb>
13 <affiliation>
14 <orgname>
15 <ulink url="http://www.linutronix.de">Linutronix</ulink>
16 </orgname>
17
18 <address>
19 <email>hjk@linutronix.de</email>
20 </address>
21 </affiliation>
22</author>
23
Mike Frysinger17149d92008-06-24 14:24:57 -070024<copyright>
25 <year>2006-2008</year>
26 <holder>Hans-Jürgen Koch.</holder>
27</copyright>
Michael S. Tsirkinccb86a62009-07-20 10:29:34 +030028<copyright>
29 <year>2009</year>
30 <holder>Red Hat Inc, Michael S. Tsirkin (mst@redhat.com)</holder>
31</copyright>
Mike Frysinger17149d92008-06-24 14:24:57 -070032
33<legalnotice>
34<para>
35This documentation is Free Software licensed under the terms of the
36GPL version 2.
37</para>
38</legalnotice>
39
Hans J. Koche3e0a282006-12-11 16:59:59 +010040<pubdate>2006-12-11</pubdate>
41
42<abstract>
43 <para>This HOWTO describes concept and usage of Linux kernel's
44 Userspace I/O system.</para>
45</abstract>
46
47<revhistory>
48 <revision>
Michael S. Tsirkinccb86a62009-07-20 10:29:34 +030049 <revnumber>0.9</revnumber>
50 <date>2009-07-16</date>
51 <authorinitials>mst</authorinitials>
52 <revremark>Added generic pci driver
53 </revremark>
54 </revision>
55 <revision>
Hans J. Koch82057792009-01-07 00:15:39 +010056 <revnumber>0.8</revnumber>
57 <date>2008-12-24</date>
58 <authorinitials>hjk</authorinitials>
59 <revremark>Added name attributes in mem and portio sysfs directories.
60 </revremark>
61 </revision>
62 <revision>
Hans J. Koch6a1b6992009-01-07 00:12:37 +010063 <revnumber>0.7</revnumber>
64 <date>2008-12-23</date>
65 <authorinitials>hjk</authorinitials>
66 <revremark>Added generic platform drivers and offset attribute.</revremark>
67 </revision>
68 <revision>
Hans J. Kocha2ab3d32008-12-06 02:25:13 +010069 <revnumber>0.6</revnumber>
70 <date>2008-12-05</date>
71 <authorinitials>hjk</authorinitials>
72 <revremark>Added description of portio sysfs attributes.</revremark>
73 </revision>
74 <revision>
Hans J. Koch328a14e2008-05-23 13:50:14 +020075 <revnumber>0.5</revnumber>
76 <date>2008-05-22</date>
77 <authorinitials>hjk</authorinitials>
78 <revremark>Added description of write() function.</revremark>
79 </revision>
80 <revision>
Hans J Koched423c22007-11-26 22:03:29 +010081 <revnumber>0.4</revnumber>
82 <date>2007-11-26</date>
83 <authorinitials>hjk</authorinitials>
84 <revremark>Removed section about uio_dummy.</revremark>
85 </revision>
86 <revision>
Hans J. Koche3e0a282006-12-11 16:59:59 +010087 <revnumber>0.3</revnumber>
88 <date>2007-04-29</date>
89 <authorinitials>hjk</authorinitials>
90 <revremark>Added section about userspace drivers.</revremark>
91 </revision>
92 <revision>
93 <revnumber>0.2</revnumber>
94 <date>2007-02-13</date>
95 <authorinitials>hjk</authorinitials>
96 <revremark>Update after multiple mappings were added.</revremark>
97 </revision>
98 <revision>
99 <revnumber>0.1</revnumber>
100 <date>2006-12-11</date>
101 <authorinitials>hjk</authorinitials>
102 <revremark>First draft.</revremark>
103 </revision>
104</revhistory>
105</bookinfo>
106
107<chapter id="aboutthisdoc">
Mike Frysinger4f7e5302008-06-24 14:25:00 -0700108<?dbhtml filename="aboutthis.html"?>
Hans J. Koche3e0a282006-12-11 16:59:59 +0100109<title>About this document</title>
110
Hans J. Koche3e0a282006-12-11 16:59:59 +0100111<sect1 id="translations">
112<?dbhtml filename="translations.html"?>
113<title>Translations</title>
114
115<para>If you know of any translations for this document, or you are
116interested in translating it, please email me
117<email>hjk@linutronix.de</email>.
118</para>
119</sect1>
120
121<sect1 id="preface">
122<title>Preface</title>
123 <para>
124 For many types of devices, creating a Linux kernel driver is
125 overkill. All that is really needed is some way to handle an
126 interrupt and provide access to the memory space of the
127 device. The logic of controlling the device does not
128 necessarily have to be within the kernel, as the device does
129 not need to take advantage of any of other resources that the
130 kernel provides. One such common class of devices that are
131 like this are for industrial I/O cards.
132 </para>
133 <para>
134 To address this situation, the userspace I/O system (UIO) was
135 designed. For typical industrial I/O cards, only a very small
136 kernel module is needed. The main part of the driver will run in
137 user space. This simplifies development and reduces the risk of
138 serious bugs within a kernel module.
139 </para>
Hans J Koched423c22007-11-26 22:03:29 +0100140 <para>
141 Please note that UIO is not an universal driver interface. Devices
142 that are already handled well by other kernel subsystems (like
143 networking or serial or USB) are no candidates for an UIO driver.
144 Hardware that is ideally suited for an UIO driver fulfills all of
145 the following:
146 </para>
147<itemizedlist>
148<listitem>
149 <para>The device has memory that can be mapped. The device can be
150 controlled completely by writing to this memory.</para>
151</listitem>
152<listitem>
153 <para>The device usually generates interrupts.</para>
154</listitem>
155<listitem>
156 <para>The device does not fit into one of the standard kernel
157 subsystems.</para>
158</listitem>
159</itemizedlist>
Hans J. Koche3e0a282006-12-11 16:59:59 +0100160</sect1>
161
162<sect1 id="thanks">
163<title>Acknowledgments</title>
164 <para>I'd like to thank Thomas Gleixner and Benedikt Spranger of
165 Linutronix, who have not only written most of the UIO code, but also
166 helped greatly writing this HOWTO by giving me all kinds of background
167 information.</para>
168</sect1>
169
170<sect1 id="feedback">
171<title>Feedback</title>
172 <para>Find something wrong with this document? (Or perhaps something
173 right?) I would love to hear from you. Please email me at
174 <email>hjk@linutronix.de</email>.</para>
175</sect1>
176</chapter>
177
178<chapter id="about">
179<?dbhtml filename="about.html"?>
180<title>About UIO</title>
181
182<para>If you use UIO for your card's driver, here's what you get:</para>
183
184<itemizedlist>
185<listitem>
186 <para>only one small kernel module to write and maintain.</para>
187</listitem>
188<listitem>
189 <para>develop the main part of your driver in user space,
190 with all the tools and libraries you're used to.</para>
191</listitem>
192<listitem>
193 <para>bugs in your driver won't crash the kernel.</para>
194</listitem>
195<listitem>
196 <para>updates of your driver can take place without recompiling
197 the kernel.</para>
198</listitem>
Hans J. Koche3e0a282006-12-11 16:59:59 +0100199</itemizedlist>
200
201<sect1 id="how_uio_works">
202<title>How UIO works</title>
203 <para>
204 Each UIO device is accessed through a device file and several
205 sysfs attribute files. The device file will be called
206 <filename>/dev/uio0</filename> for the first device, and
207 <filename>/dev/uio1</filename>, <filename>/dev/uio2</filename>
208 and so on for subsequent devices.
209 </para>
210
211 <para><filename>/dev/uioX</filename> is used to access the
212 address space of the card. Just use
213 <function>mmap()</function> to access registers or RAM
214 locations of your card.
215 </para>
216
217 <para>
218 Interrupts are handled by reading from
219 <filename>/dev/uioX</filename>. A blocking
220 <function>read()</function> from
221 <filename>/dev/uioX</filename> will return as soon as an
222 interrupt occurs. You can also use
223 <function>select()</function> on
224 <filename>/dev/uioX</filename> to wait for an interrupt. The
225 integer value read from <filename>/dev/uioX</filename>
226 represents the total interrupt count. You can use this number
227 to figure out if you missed some interrupts.
228 </para>
Hans J. Koch328a14e2008-05-23 13:50:14 +0200229 <para>
230 For some hardware that has more than one interrupt source internally,
231 but not separate IRQ mask and status registers, there might be
232 situations where userspace cannot determine what the interrupt source
233 was if the kernel handler disables them by writing to the chip's IRQ
234 register. In such a case, the kernel has to disable the IRQ completely
235 to leave the chip's register untouched. Now the userspace part can
236 determine the cause of the interrupt, but it cannot re-enable
237 interrupts. Another cornercase is chips where re-enabling interrupts
238 is a read-modify-write operation to a combined IRQ status/acknowledge
239 register. This would be racy if a new interrupt occurred
240 simultaneously.
241 </para>
242 <para>
243 To address these problems, UIO also implements a write() function. It
244 is normally not used and can be ignored for hardware that has only a
245 single interrupt source or has separate IRQ mask and status registers.
246 If you need it, however, a write to <filename>/dev/uioX</filename>
247 will call the <function>irqcontrol()</function> function implemented
248 by the driver. You have to write a 32-bit value that is usually either
249 0 or 1 to disable or enable interrupts. If a driver does not implement
250 <function>irqcontrol()</function>, <function>write()</function> will
251 return with <varname>-ENOSYS</varname>.
252 </para>
Hans J. Koche3e0a282006-12-11 16:59:59 +0100253
254 <para>
255 To handle interrupts properly, your custom kernel module can
256 provide its own interrupt handler. It will automatically be
257 called by the built-in handler.
258 </para>
259
260 <para>
261 For cards that don't generate interrupts but need to be
262 polled, there is the possibility to set up a timer that
263 triggers the interrupt handler at configurable time intervals.
Hans J Koched423c22007-11-26 22:03:29 +0100264 This interrupt simulation is done by calling
265 <function>uio_event_notify()</function>
266 from the timer's event handler.
Hans J. Koche3e0a282006-12-11 16:59:59 +0100267 </para>
268
269 <para>
270 Each driver provides attributes that are used to read or write
271 variables. These attributes are accessible through sysfs
272 files. A custom kernel driver module can add its own
273 attributes to the device owned by the uio driver, but not added
274 to the UIO device itself at this time. This might change in the
275 future if it would be found to be useful.
276 </para>
277
278 <para>
279 The following standard attributes are provided by the UIO
280 framework:
281 </para>
282<itemizedlist>
283<listitem>
284 <para>
285 <filename>name</filename>: The name of your device. It is
286 recommended to use the name of your kernel module for this.
287 </para>
288</listitem>
289<listitem>
290 <para>
291 <filename>version</filename>: A version string defined by your
292 driver. This allows the user space part of your driver to deal
293 with different versions of the kernel module.
294 </para>
295</listitem>
296<listitem>
297 <para>
298 <filename>event</filename>: The total number of interrupts
299 handled by the driver since the last time the device node was
300 read.
301 </para>
302</listitem>
303</itemizedlist>
304<para>
305 These attributes appear under the
306 <filename>/sys/class/uio/uioX</filename> directory. Please
307 note that this directory might be a symlink, and not a real
308 directory. Any userspace code that accesses it must be able
309 to handle this.
310</para>
311<para>
312 Each UIO device can make one or more memory regions available for
313 memory mapping. This is necessary because some industrial I/O cards
314 require access to more than one PCI memory region in a driver.
315</para>
316<para>
317 Each mapping has its own directory in sysfs, the first mapping
318 appears as <filename>/sys/class/uio/uioX/maps/map0/</filename>.
319 Subsequent mappings create directories <filename>map1/</filename>,
320 <filename>map2/</filename>, and so on. These directories will only
321 appear if the size of the mapping is not 0.
322</para>
323<para>
Hans J. Koch82057792009-01-07 00:15:39 +0100324 Each <filename>mapX/</filename> directory contains four read-only files
325 that show attributes of the memory:
Hans J. Koche3e0a282006-12-11 16:59:59 +0100326</para>
327<itemizedlist>
328<listitem>
329 <para>
Hans J. Koch82057792009-01-07 00:15:39 +0100330 <filename>name</filename>: A string identifier for this mapping. This
331 is optional, the string can be empty. Drivers can set this to make it
332 easier for userspace to find the correct mapping.
333 </para>
334</listitem>
335<listitem>
336 <para>
Hans J. Koche3e0a282006-12-11 16:59:59 +0100337 <filename>addr</filename>: The address of memory that can be mapped.
338 </para>
339</listitem>
340<listitem>
341 <para>
342 <filename>size</filename>: The size, in bytes, of the memory
343 pointed to by addr.
344 </para>
345</listitem>
Hans J. Koch6a1b6992009-01-07 00:12:37 +0100346<listitem>
347 <para>
348 <filename>offset</filename>: The offset, in bytes, that has to be
349 added to the pointer returned by <function>mmap()</function> to get
350 to the actual device memory. This is important if the device's memory
351 is not page aligned. Remember that pointers returned by
352 <function>mmap()</function> are always page aligned, so it is good
353 style to always add this offset.
354 </para>
355</listitem>
Hans J. Koche3e0a282006-12-11 16:59:59 +0100356</itemizedlist>
357
358<para>
359 From userspace, the different mappings are distinguished by adjusting
360 the <varname>offset</varname> parameter of the
361 <function>mmap()</function> call. To map the memory of mapping N, you
362 have to use N times the page size as your offset:
363</para>
364<programlisting format="linespecific">
365offset = N * getpagesize();
366</programlisting>
367
Hans J. Kocha2ab3d32008-12-06 02:25:13 +0100368<para>
369 Sometimes there is hardware with memory-like regions that can not be
370 mapped with the technique described here, but there are still ways to
371 access them from userspace. The most common example are x86 ioports.
372 On x86 systems, userspace can access these ioports using
373 <function>ioperm()</function>, <function>iopl()</function>,
374 <function>inb()</function>, <function>outb()</function>, and similar
375 functions.
376</para>
377<para>
378 Since these ioport regions can not be mapped, they will not appear under
379 <filename>/sys/class/uio/uioX/maps/</filename> like the normal memory
380 described above. Without information about the port regions a hardware
381 has to offer, it becomes difficult for the userspace part of the
382 driver to find out which ports belong to which UIO device.
383</para>
384<para>
385 To address this situation, the new directory
386 <filename>/sys/class/uio/uioX/portio/</filename> was added. It only
387 exists if the driver wants to pass information about one or more port
388 regions to userspace. If that is the case, subdirectories named
389 <filename>port0</filename>, <filename>port1</filename>, and so on,
390 will appear underneath
391 <filename>/sys/class/uio/uioX/portio/</filename>.
392</para>
393<para>
Hans J. Koch82057792009-01-07 00:15:39 +0100394 Each <filename>portX/</filename> directory contains four read-only
395 files that show name, start, size, and type of the port region:
Hans J. Kocha2ab3d32008-12-06 02:25:13 +0100396</para>
397<itemizedlist>
398<listitem>
399 <para>
Hans J. Koch82057792009-01-07 00:15:39 +0100400 <filename>name</filename>: A string identifier for this port region.
401 The string is optional and can be empty. Drivers can set it to make it
402 easier for userspace to find a certain port region.
403 </para>
404</listitem>
405<listitem>
406 <para>
Hans J. Kocha2ab3d32008-12-06 02:25:13 +0100407 <filename>start</filename>: The first port of this region.
408 </para>
409</listitem>
410<listitem>
411 <para>
412 <filename>size</filename>: The number of ports in this region.
413 </para>
414</listitem>
415<listitem>
416 <para>
417 <filename>porttype</filename>: A string describing the type of port.
418 </para>
419</listitem>
420</itemizedlist>
421
422
Hans J. Koche3e0a282006-12-11 16:59:59 +0100423</sect1>
424</chapter>
425
Hans J. Koche3e0a282006-12-11 16:59:59 +0100426<chapter id="custom_kernel_module" xreflabel="Writing your own kernel module">
427<?dbhtml filename="custom_kernel_module.html"?>
428<title>Writing your own kernel module</title>
429 <para>
Hans J Koched423c22007-11-26 22:03:29 +0100430 Please have a look at <filename>uio_cif.c</filename> as an
Hans J. Koche3e0a282006-12-11 16:59:59 +0100431 example. The following paragraphs explain the different
432 sections of this file.
433 </para>
434
435<sect1 id="uio_info">
436<title>struct uio_info</title>
437 <para>
438 This structure tells the framework the details of your driver,
439 Some of the members are required, others are optional.
440 </para>
441
442<itemizedlist>
443<listitem><para>
Stephen Rothwellb8ac9fc2008-12-12 11:44:21 +0100444<varname>const char *name</varname>: Required. The name of your driver as
Hans J. Koche3e0a282006-12-11 16:59:59 +0100445it will appear in sysfs. I recommend using the name of your module for this.
446</para></listitem>
447
448<listitem><para>
Stephen Rothwellb8ac9fc2008-12-12 11:44:21 +0100449<varname>const char *version</varname>: Required. This string appears in
Hans J. Koche3e0a282006-12-11 16:59:59 +0100450<filename>/sys/class/uio/uioX/version</filename>.
451</para></listitem>
452
453<listitem><para>
454<varname>struct uio_mem mem[ MAX_UIO_MAPS ]</varname>: Required if you
455have memory that can be mapped with <function>mmap()</function>. For each
456mapping you need to fill one of the <varname>uio_mem</varname> structures.
457See the description below for details.
458</para></listitem>
459
460<listitem><para>
Hans J. Kocha2ab3d32008-12-06 02:25:13 +0100461<varname>struct uio_port port[ MAX_UIO_PORTS_REGIONS ]</varname>: Required
462if you want to pass information about ioports to userspace. For each port
463region you need to fill one of the <varname>uio_port</varname> structures.
464See the description below for details.
465</para></listitem>
466
467<listitem><para>
Hans J. Koche3e0a282006-12-11 16:59:59 +0100468<varname>long irq</varname>: Required. If your hardware generates an
469interrupt, it's your modules task to determine the irq number during
470initialization. If you don't have a hardware generated interrupt but
471want to trigger the interrupt handler in some other way, set
Hans J Koched423c22007-11-26 22:03:29 +0100472<varname>irq</varname> to <varname>UIO_IRQ_CUSTOM</varname>.
473If you had no interrupt at all, you could set
Hans J. Koche3e0a282006-12-11 16:59:59 +0100474<varname>irq</varname> to <varname>UIO_IRQ_NONE</varname>, though this
475rarely makes sense.
476</para></listitem>
477
478<listitem><para>
479<varname>unsigned long irq_flags</varname>: Required if you've set
480<varname>irq</varname> to a hardware interrupt number. The flags given
481here will be used in the call to <function>request_irq()</function>.
482</para></listitem>
483
484<listitem><para>
485<varname>int (*mmap)(struct uio_info *info, struct vm_area_struct
486*vma)</varname>: Optional. If you need a special
487<function>mmap()</function> function, you can set it here. If this
488pointer is not NULL, your <function>mmap()</function> will be called
489instead of the built-in one.
490</para></listitem>
491
492<listitem><para>
493<varname>int (*open)(struct uio_info *info, struct inode *inode)
494</varname>: Optional. You might want to have your own
495<function>open()</function>, e.g. to enable interrupts only when your
496device is actually used.
497</para></listitem>
498
499<listitem><para>
500<varname>int (*release)(struct uio_info *info, struct inode *inode)
501</varname>: Optional. If you define your own
502<function>open()</function>, you will probably also want a custom
503<function>release()</function> function.
504</para></listitem>
Hans J. Koch328a14e2008-05-23 13:50:14 +0200505
506<listitem><para>
507<varname>int (*irqcontrol)(struct uio_info *info, s32 irq_on)
508</varname>: Optional. If you need to be able to enable or disable
509interrupts from userspace by writing to <filename>/dev/uioX</filename>,
510you can implement this function. The parameter <varname>irq_on</varname>
511will be 0 to disable interrupts and 1 to enable them.
512</para></listitem>
Hans J. Koche3e0a282006-12-11 16:59:59 +0100513</itemizedlist>
514
515<para>
516Usually, your device will have one or more memory regions that can be mapped
517to user space. For each region, you have to set up a
518<varname>struct uio_mem</varname> in the <varname>mem[]</varname> array.
519Here's a description of the fields of <varname>struct uio_mem</varname>:
520</para>
521
522<itemizedlist>
523<listitem><para>
524<varname>int memtype</varname>: Required if the mapping is used. Set this to
525<varname>UIO_MEM_PHYS</varname> if you you have physical memory on your
526card to be mapped. Use <varname>UIO_MEM_LOGICAL</varname> for logical
527memory (e.g. allocated with <function>kmalloc()</function>). There's also
528<varname>UIO_MEM_VIRTUAL</varname> for virtual memory.
529</para></listitem>
530
531<listitem><para>
532<varname>unsigned long addr</varname>: Required if the mapping is used.
533Fill in the address of your memory block. This address is the one that
534appears in sysfs.
535</para></listitem>
536
537<listitem><para>
538<varname>unsigned long size</varname>: Fill in the size of the
539memory block that <varname>addr</varname> points to. If <varname>size</varname>
540is zero, the mapping is considered unused. Note that you
541<emphasis>must</emphasis> initialize <varname>size</varname> with zero for
542all unused mappings.
543</para></listitem>
544
545<listitem><para>
546<varname>void *internal_addr</varname>: If you have to access this memory
547region from within your kernel module, you will want to map it internally by
548using something like <function>ioremap()</function>. Addresses
549returned by this function cannot be mapped to user space, so you must not
550store it in <varname>addr</varname>. Use <varname>internal_addr</varname>
551instead to remember such an address.
552</para></listitem>
553</itemizedlist>
554
555<para>
556Please do not touch the <varname>kobj</varname> element of
557<varname>struct uio_mem</varname>! It is used by the UIO framework
558to set up sysfs files for this mapping. Simply leave it alone.
559</para>
Hans J. Kocha2ab3d32008-12-06 02:25:13 +0100560
561<para>
562Sometimes, your device can have one or more port regions which can not be
563mapped to userspace. But if there are other possibilities for userspace to
564access these ports, it makes sense to make information about the ports
565available in sysfs. For each region, you have to set up a
566<varname>struct uio_port</varname> in the <varname>port[]</varname> array.
567Here's a description of the fields of <varname>struct uio_port</varname>:
568</para>
569
570<itemizedlist>
571<listitem><para>
572<varname>char *porttype</varname>: Required. Set this to one of the predefined
573constants. Use <varname>UIO_PORT_X86</varname> for the ioports found in x86
574architectures.
575</para></listitem>
576
577<listitem><para>
578<varname>unsigned long start</varname>: Required if the port region is used.
579Fill in the number of the first port of this region.
580</para></listitem>
581
582<listitem><para>
583<varname>unsigned long size</varname>: Fill in the number of ports in this
584region. If <varname>size</varname> is zero, the region is considered unused.
585Note that you <emphasis>must</emphasis> initialize <varname>size</varname>
586with zero for all unused regions.
587</para></listitem>
588</itemizedlist>
589
590<para>
591Please do not touch the <varname>portio</varname> element of
592<varname>struct uio_port</varname>! It is used internally by the UIO
593framework to set up sysfs files for this region. Simply leave it alone.
594</para>
595
Hans J. Koche3e0a282006-12-11 16:59:59 +0100596</sect1>
597
598<sect1 id="adding_irq_handler">
599<title>Adding an interrupt handler</title>
600 <para>
601 What you need to do in your interrupt handler depends on your
602 hardware and on how you want to handle it. You should try to
603 keep the amount of code in your kernel interrupt handler low.
604 If your hardware requires no action that you
605 <emphasis>have</emphasis> to perform after each interrupt,
606 then your handler can be empty.</para> <para>If, on the other
607 hand, your hardware <emphasis>needs</emphasis> some action to
608 be performed after each interrupt, then you
609 <emphasis>must</emphasis> do it in your kernel module. Note
610 that you cannot rely on the userspace part of your driver. Your
611 userspace program can terminate at any time, possibly leaving
612 your hardware in a state where proper interrupt handling is
613 still required.
614 </para>
615
616 <para>
617 There might also be applications where you want to read data
618 from your hardware at each interrupt and buffer it in a piece
619 of kernel memory you've allocated for that purpose. With this
620 technique you could avoid loss of data if your userspace
621 program misses an interrupt.
622 </para>
623
624 <para>
625 A note on shared interrupts: Your driver should support
626 interrupt sharing whenever this is possible. It is possible if
627 and only if your driver can detect whether your hardware has
628 triggered the interrupt or not. This is usually done by looking
629 at an interrupt status register. If your driver sees that the
630 IRQ bit is actually set, it will perform its actions, and the
631 handler returns IRQ_HANDLED. If the driver detects that it was
632 not your hardware that caused the interrupt, it will do nothing
633 and return IRQ_NONE, allowing the kernel to call the next
634 possible interrupt handler.
635 </para>
636
637 <para>
638 If you decide not to support shared interrupts, your card
639 won't work in computers with no free interrupts. As this
640 frequently happens on the PC platform, you can save yourself a
641 lot of trouble by supporting interrupt sharing.
642 </para>
643</sect1>
644
Hans J. Koch6a1b6992009-01-07 00:12:37 +0100645<sect1 id="using_uio_pdrv">
646<title>Using uio_pdrv for platform devices</title>
647 <para>
648 In many cases, UIO drivers for platform devices can be handled in a
649 generic way. In the same place where you define your
650 <varname>struct platform_device</varname>, you simply also implement
651 your interrupt handler and fill your
652 <varname>struct uio_info</varname>. A pointer to this
653 <varname>struct uio_info</varname> is then used as
654 <varname>platform_data</varname> for your platform device.
655 </para>
656 <para>
657 You also need to set up an array of <varname>struct resource</varname>
658 containing addresses and sizes of your memory mappings. This
659 information is passed to the driver using the
660 <varname>.resource</varname> and <varname>.num_resources</varname>
661 elements of <varname>struct platform_device</varname>.
662 </para>
663 <para>
664 You now have to set the <varname>.name</varname> element of
665 <varname>struct platform_device</varname> to
666 <varname>"uio_pdrv"</varname> to use the generic UIO platform device
667 driver. This driver will fill the <varname>mem[]</varname> array
668 according to the resources given, and register the device.
669 </para>
670 <para>
671 The advantage of this approach is that you only have to edit a file
672 you need to edit anyway. You do not have to create an extra driver.
673 </para>
674</sect1>
675
676<sect1 id="using_uio_pdrv_genirq">
677<title>Using uio_pdrv_genirq for platform devices</title>
678 <para>
679 Especially in embedded devices, you frequently find chips where the
680 irq pin is tied to its own dedicated interrupt line. In such cases,
681 where you can be really sure the interrupt is not shared, we can take
682 the concept of <varname>uio_pdrv</varname> one step further and use a
683 generic interrupt handler. That's what
684 <varname>uio_pdrv_genirq</varname> does.
685 </para>
686 <para>
687 The setup for this driver is the same as described above for
688 <varname>uio_pdrv</varname>, except that you do not implement an
689 interrupt handler. The <varname>.handler</varname> element of
690 <varname>struct uio_info</varname> must remain
691 <varname>NULL</varname>. The <varname>.irq_flags</varname> element
692 must not contain <varname>IRQF_SHARED</varname>.
693 </para>
694 <para>
695 You will set the <varname>.name</varname> element of
696 <varname>struct platform_device</varname> to
697 <varname>"uio_pdrv_genirq"</varname> to use this driver.
698 </para>
699 <para>
700 The generic interrupt handler of <varname>uio_pdrv_genirq</varname>
701 will simply disable the interrupt line using
702 <function>disable_irq_nosync()</function>. After doing its work,
703 userspace can reenable the interrupt by writing 0x00000001 to the UIO
704 device file. The driver already implements an
705 <function>irq_control()</function> to make this possible, you must not
706 implement your own.
707 </para>
708 <para>
709 Using <varname>uio_pdrv_genirq</varname> not only saves a few lines of
710 interrupt handler code. You also do not need to know anything about
711 the chip's internal registers to create the kernel part of the driver.
712 All you need to know is the irq number of the pin the chip is
713 connected to.
714 </para>
715</sect1>
716
Hans J. Koche3e0a282006-12-11 16:59:59 +0100717</chapter>
718
719<chapter id="userspace_driver" xreflabel="Writing a driver in user space">
720<?dbhtml filename="userspace_driver.html"?>
721<title>Writing a driver in userspace</title>
722 <para>
723 Once you have a working kernel module for your hardware, you can
724 write the userspace part of your driver. You don't need any special
725 libraries, your driver can be written in any reasonable language,
726 you can use floating point numbers and so on. In short, you can
727 use all the tools and libraries you'd normally use for writing a
728 userspace application.
729 </para>
730
731<sect1 id="getting_uio_information">
732<title>Getting information about your UIO device</title>
733 <para>
734 Information about all UIO devices is available in sysfs. The
735 first thing you should do in your driver is check
736 <varname>name</varname> and <varname>version</varname> to
737 make sure your talking to the right device and that its kernel
738 driver has the version you expect.
739 </para>
740 <para>
741 You should also make sure that the memory mapping you need
742 exists and has the size you expect.
743 </para>
744 <para>
745 There is a tool called <varname>lsuio</varname> that lists
746 UIO devices and their attributes. It is available here:
747 </para>
748 <para>
749 <ulink url="http://www.osadl.org/projects/downloads/UIO/user/">
750 http://www.osadl.org/projects/downloads/UIO/user/</ulink>
751 </para>
752 <para>
753 With <varname>lsuio</varname> you can quickly check if your
754 kernel module is loaded and which attributes it exports.
755 Have a look at the manpage for details.
756 </para>
757 <para>
758 The source code of <varname>lsuio</varname> can serve as an
759 example for getting information about an UIO device.
760 The file <filename>uio_helper.c</filename> contains a lot of
761 functions you could use in your userspace driver code.
762 </para>
763</sect1>
764
765<sect1 id="mmap_device_memory">
766<title>mmap() device memory</title>
767 <para>
768 After you made sure you've got the right device with the
769 memory mappings you need, all you have to do is to call
770 <function>mmap()</function> to map the device's memory
771 to userspace.
772 </para>
773 <para>
774 The parameter <varname>offset</varname> of the
775 <function>mmap()</function> call has a special meaning
776 for UIO devices: It is used to select which mapping of
777 your device you want to map. To map the memory of
778 mapping N, you have to use N times the page size as
779 your offset:
780 </para>
781<programlisting format="linespecific">
782 offset = N * getpagesize();
783</programlisting>
784 <para>
785 N starts from zero, so if you've got only one memory
786 range to map, set <varname>offset = 0</varname>.
787 A drawback of this technique is that memory is always
788 mapped beginning with its start address.
789 </para>
790</sect1>
791
792<sect1 id="wait_for_interrupts">
793<title>Waiting for interrupts</title>
794 <para>
795 After you successfully mapped your devices memory, you
796 can access it like an ordinary array. Usually, you will
797 perform some initialization. After that, your hardware
798 starts working and will generate an interrupt as soon
799 as it's finished, has some data available, or needs your
800 attention because an error occured.
801 </para>
802 <para>
803 <filename>/dev/uioX</filename> is a read-only file. A
804 <function>read()</function> will always block until an
805 interrupt occurs. There is only one legal value for the
806 <varname>count</varname> parameter of
807 <function>read()</function>, and that is the size of a
808 signed 32 bit integer (4). Any other value for
809 <varname>count</varname> causes <function>read()</function>
810 to fail. The signed 32 bit integer read is the interrupt
811 count of your device. If the value is one more than the value
812 you read the last time, everything is OK. If the difference
813 is greater than one, you missed interrupts.
814 </para>
815 <para>
816 You can also use <function>select()</function> on
817 <filename>/dev/uioX</filename>.
818 </para>
819</sect1>
820
821</chapter>
822
Michael S. Tsirkinccb86a62009-07-20 10:29:34 +0300823<chapter id="uio_pci_generic" xreflabel="Using Generic driver for PCI cards">
824<?dbhtml filename="uio_pci_generic.html"?>
825<title>Generic PCI UIO driver</title>
826 <para>
827 The generic driver is a kernel module named uio_pci_generic.
828 It can work with any device compliant to PCI 2.3 (circa 2002) and
829 any compliant PCI Express device. Using this, you only need to
830 write the userspace driver, removing the need to write
831 a hardware-specific kernel module.
832 </para>
833
834<sect1 id="uio_pci_generic_binding">
835<title>Making the driver recognize the device</title>
836 <para>
837Since the driver does not declare any device ids, it will not get loaded
838automatically and will not automatically bind to any devices, you must load it
839and allocate id to the driver yourself. For example:
840 <programlisting>
841 modprobe uio_pci_generic
842 echo &quot;8086 10f5&quot; &gt; /sys/bus/pci/drivers/uio_pci_generic/new_id
843 </programlisting>
844 </para>
845 <para>
846If there already is a hardware specific kernel driver for your device, the
847generic driver still won't bind to it, in this case if you want to use the
848generic driver (why would you?) you'll have to manually unbind the hardware
849specific driver and bind the generic driver, like this:
850 <programlisting>
851 echo -n 0000:00:19.0 &gt; /sys/bus/pci/drivers/e1000e/unbind
852 echo -n 0000:00:19.0 &gt; /sys/bus/pci/drivers/uio_pci_generic/bind
853 </programlisting>
854 </para>
855 <para>
856You can verify that the device has been bound to the driver
857by looking for it in sysfs, for example like the following:
858 <programlisting>
859 ls -l /sys/bus/pci/devices/0000:00:19.0/driver
860 </programlisting>
861Which if successful should print
862 <programlisting>
863 .../0000:00:19.0/driver -&gt; ../../../bus/pci/drivers/uio_pci_generic
864 </programlisting>
865Note that the generic driver will not bind to old PCI 2.2 devices.
866If binding the device failed, run the following command:
867 <programlisting>
868 dmesg
869 </programlisting>
870and look in the output for failure reasons
871 </para>
872</sect1>
873
874<sect1 id="uio_pci_generic_internals">
875<title>Things to know about uio_pci_generic</title>
876 <para>
877Interrupts are handled using the Interrupt Disable bit in the PCI command
878register and Interrupt Status bit in the PCI status register. All devices
879compliant to PCI 2.3 (circa 2002) and all compliant PCI Express devices should
880support these bits. uio_pci_generic detects this support, and won't bind to
881devices which do not support the Interrupt Disable Bit in the command register.
882 </para>
883 <para>
884On each interrupt, uio_pci_generic sets the Interrupt Disable bit.
885This prevents the device from generating further interrupts
886until the bit is cleared. The userspace driver should clear this
887bit before blocking and waiting for more interrupts.
888 </para>
889</sect1>
890<sect1 id="uio_pci_generic_userspace">
891<title>Writing userspace driver using uio_pci_generic</title>
892 <para>
893Userspace driver can use pci sysfs interface, or the
894libpci libray that wraps it, to talk to the device and to
895re-enable interrupts by writing to the command register.
896 </para>
897</sect1>
898<sect1 id="uio_pci_generic_example">
899<title>Example code using uio_pci_generic</title>
900 <para>
901Here is some sample userspace driver code using uio_pci_generic:
902<programlisting>
903#include &lt;stdlib.h&gt;
904#include &lt;stdio.h&gt;
905#include &lt;unistd.h&gt;
906#include &lt;sys/types.h&gt;
907#include &lt;sys/stat.h&gt;
908#include &lt;fcntl.h&gt;
909#include &lt;errno.h&gt;
910
911int main()
912{
913 int uiofd;
914 int configfd;
915 int err;
916 int i;
917 unsigned icount;
918 unsigned char command_high;
919
920 uiofd = open(&quot;/dev/uio0&quot;, O_RDONLY);
921 if (uiofd &lt; 0) {
922 perror(&quot;uio open:&quot;);
923 return errno;
924 }
925 configfd = open(&quot;/sys/class/uio/uio0/device/config&quot;, O_RDWR);
926 if (uiofd &lt; 0) {
927 perror(&quot;config open:&quot;);
928 return errno;
929 }
930
931 /* Read and cache command value */
932 err = pread(configfd, &amp;command_high, 1, 5);
933 if (err != 1) {
934 perror(&quot;command config read:&quot;);
935 return errno;
936 }
937 command_high &amp;= ~0x4;
938
939 for(i = 0;; ++i) {
940 /* Print out a message, for debugging. */
941 if (i == 0)
942 fprintf(stderr, &quot;Started uio test driver.\n&quot;);
943 else
944 fprintf(stderr, &quot;Interrupts: %d\n&quot;, icount);
945
946 /****************************************/
947 /* Here we got an interrupt from the
948 device. Do something to it. */
949 /****************************************/
950
951 /* Re-enable interrupts. */
952 err = pwrite(configfd, &amp;command_high, 1, 5);
953 if (err != 1) {
954 perror(&quot;config write:&quot;);
955 break;
956 }
957
958 /* Wait for next interrupt. */
959 err = read(uiofd, &amp;icount, 4);
960 if (err != 4) {
961 perror(&quot;uio read:&quot;);
962 break;
963 }
964
965 }
966 return errno;
967}
968
969</programlisting>
970 </para>
971</sect1>
972
973</chapter>
974
Hans J. Koche3e0a282006-12-11 16:59:59 +0100975<appendix id="app1">
976<title>Further information</title>
977<itemizedlist>
978 <listitem><para>
979 <ulink url="http://www.osadl.org">
980 OSADL homepage.</ulink>
981 </para></listitem>
982 <listitem><para>
983 <ulink url="http://www.linutronix.de">
984 Linutronix homepage.</ulink>
985 </para></listitem>
986</itemizedlist>
987</appendix>
988
989</book>