blob: fb10fd08c05cd00a49a4276f06842299e092b4a7 [file] [log] [blame]
Thomas Gleixner11c869e2006-06-29 02:24:47 -07001<?xml version="1.0" encoding="UTF-8"?>
2<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN"
3 "http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []>
4
5<book id="Generic-IRQ-Guide">
6 <bookinfo>
7 <title>Linux generic IRQ handling</title>
8
9 <authorgroup>
10 <author>
11 <firstname>Thomas</firstname>
12 <surname>Gleixner</surname>
13 <affiliation>
14 <address>
15 <email>tglx@linutronix.de</email>
16 </address>
17 </affiliation>
18 </author>
19 <author>
20 <firstname>Ingo</firstname>
21 <surname>Molnar</surname>
22 <affiliation>
23 <address>
24 <email>mingo@elte.hu</email>
25 </address>
26 </affiliation>
27 </author>
28 </authorgroup>
29
30 <copyright>
Thomas Gleixner25ade602010-09-30 20:33:11 +020031 <year>2005-2010</year>
Thomas Gleixner11c869e2006-06-29 02:24:47 -070032 <holder>Thomas Gleixner</holder>
33 </copyright>
34 <copyright>
35 <year>2005-2006</year>
36 <holder>Ingo Molnar</holder>
37 </copyright>
38
39 <legalnotice>
40 <para>
41 This documentation is free software; you can redistribute
42 it and/or modify it under the terms of the GNU General Public
43 License version 2 as published by the Free Software Foundation.
44 </para>
45
46 <para>
47 This program is distributed in the hope that it will be
48 useful, but WITHOUT ANY WARRANTY; without even the implied
49 warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
50 See the GNU General Public License for more details.
51 </para>
52
53 <para>
54 You should have received a copy of the GNU General Public
55 License along with this program; if not, write to the Free
56 Software Foundation, Inc., 59 Temple Place, Suite 330, Boston,
57 MA 02111-1307 USA
58 </para>
59
60 <para>
61 For more details see the file COPYING in the source
62 distribution of Linux.
63 </para>
64 </legalnotice>
65 </bookinfo>
66
67<toc></toc>
68
69 <chapter id="intro">
70 <title>Introduction</title>
71 <para>
72 The generic interrupt handling layer is designed to provide a
73 complete abstraction of interrupt handling for device drivers.
74 It is able to handle all the different types of interrupt controller
75 hardware. Device drivers use generic API functions to request, enable,
76 disable and free interrupts. The drivers do not have to know anything
77 about interrupt hardware details, so they can be used on different
78 platforms without code changes.
79 </para>
80 <para>
81 This documentation is provided to developers who want to implement
82 an interrupt subsystem based for their architecture, with the help
83 of the generic IRQ handling layer.
84 </para>
85 </chapter>
86
87 <chapter id="rationale">
88 <title>Rationale</title>
89 <para>
90 The original implementation of interrupt handling in Linux is using
91 the __do_IRQ() super-handler, which is able to deal with every
92 type of interrupt logic.
93 </para>
94 <para>
95 Originally, Russell King identified different types of handlers to
96 build a quite universal set for the ARM interrupt handler
97 implementation in Linux 2.5/2.6. He distinguished between:
98 <itemizedlist>
99 <listitem><para>Level type</para></listitem>
100 <listitem><para>Edge type</para></listitem>
101 <listitem><para>Simple type</para></listitem>
102 </itemizedlist>
Thomas Gleixner25ade602010-09-30 20:33:11 +0200103 During the implementation we identified another type:
104 <itemizedlist>
105 <listitem><para>Fast EOI type</para></listitem>
106 </itemizedlist>
Thomas Gleixner11c869e2006-06-29 02:24:47 -0700107 In the SMP world of the __do_IRQ() super-handler another type
108 was identified:
109 <itemizedlist>
110 <listitem><para>Per CPU type</para></listitem>
111 </itemizedlist>
112 </para>
113 <para>
114 This split implementation of highlevel IRQ handlers allows us to
115 optimize the flow of the interrupt handling for each specific
116 interrupt type. This reduces complexity in that particular codepath
117 and allows the optimized handling of a given type.
118 </para>
119 <para>
120 The original general IRQ implementation used hw_interrupt_type
121 structures and their ->ack(), ->end() [etc.] callbacks to
122 differentiate the flow control in the super-handler. This leads to
123 a mix of flow logic and lowlevel hardware logic, and it also leads
124 to unnecessary code duplication: for example in i386, there is a
125 ioapic_level_irq and a ioapic_edge_irq irq-type which share many
126 of the lowlevel details but have different flow handling.
127 </para>
128 <para>
129 A more natural abstraction is the clean separation of the
130 'irq flow' and the 'chip details'.
131 </para>
132 <para>
133 Analysing a couple of architecture's IRQ subsystem implementations
134 reveals that most of them can use a generic set of 'irq flow'
135 methods and only need to add the chip level specific code.
136 The separation is also valuable for (sub)architectures
137 which need specific quirks in the irq flow itself but not in the
138 chip-details - and thus provides a more transparent IRQ subsystem
139 design.
140 </para>
141 <para>
142 Each interrupt descriptor is assigned its own highlevel flow
143 handler, which is normally one of the generic
144 implementations. (This highlevel flow handler implementation also
145 makes it simple to provide demultiplexing handlers which can be
146 found in embedded platforms on various architectures.)
147 </para>
148 <para>
149 The separation makes the generic interrupt handling layer more
150 flexible and extensible. For example, an (sub)architecture can
151 use a generic irq-flow implementation for 'level type' interrupts
152 and add a (sub)architecture specific 'edge type' implementation.
153 </para>
154 <para>
155 To make the transition to the new model easier and prevent the
156 breakage of existing implementations, the __do_IRQ() super-handler
157 is still available. This leads to a kind of duality for the time
158 being. Over time the new model should be used in more and more
159 architectures, as it enables smaller and cleaner IRQ subsystems.
Thomas Gleixner25ade602010-09-30 20:33:11 +0200160 It's deprecated for three years now and about to be removed.
Thomas Gleixner11c869e2006-06-29 02:24:47 -0700161 </para>
162 </chapter>
163 <chapter id="bugs">
164 <title>Known Bugs And Assumptions</title>
165 <para>
166 None (knock on wood).
167 </para>
168 </chapter>
169
170 <chapter id="Abstraction">
171 <title>Abstraction layers</title>
172 <para>
173 There are three main levels of abstraction in the interrupt code:
174 <orderedlist>
175 <listitem><para>Highlevel driver API</para></listitem>
176 <listitem><para>Highlevel IRQ flow handlers</para></listitem>
177 <listitem><para>Chiplevel hardware encapsulation</para></listitem>
178 </orderedlist>
179 </para>
Rob Landleyaa9128f2008-02-07 00:13:28 -0800180 <sect1 id="Interrupt_control_flow">
Thomas Gleixner11c869e2006-06-29 02:24:47 -0700181 <title>Interrupt control flow</title>
182 <para>
183 Each interrupt is described by an interrupt descriptor structure
184 irq_desc. The interrupt is referenced by an 'unsigned int' numeric
185 value which selects the corresponding interrupt decription structure
186 in the descriptor structures array.
187 The descriptor structure contains status information and pointers
188 to the interrupt flow method and the interrupt chip structure
189 which are assigned to this interrupt.
190 </para>
191 <para>
192 Whenever an interrupt triggers, the lowlevel arch code calls into
193 the generic interrupt code by calling desc->handle_irq().
194 This highlevel IRQ handling function only uses desc->chip primitives
195 referenced by the assigned chip descriptor structure.
196 </para>
197 </sect1>
Rob Landleyaa9128f2008-02-07 00:13:28 -0800198 <sect1 id="Highlevel_Driver_API">
Thomas Gleixner11c869e2006-06-29 02:24:47 -0700199 <title>Highlevel Driver API</title>
200 <para>
201 The highlevel Driver API consists of following functions:
202 <itemizedlist>
203 <listitem><para>request_irq()</para></listitem>
204 <listitem><para>free_irq()</para></listitem>
205 <listitem><para>disable_irq()</para></listitem>
206 <listitem><para>enable_irq()</para></listitem>
207 <listitem><para>disable_irq_nosync() (SMP only)</para></listitem>
208 <listitem><para>synchronize_irq() (SMP only)</para></listitem>
209 <listitem><para>set_irq_type()</para></listitem>
210 <listitem><para>set_irq_wake()</para></listitem>
211 <listitem><para>set_irq_data()</para></listitem>
212 <listitem><para>set_irq_chip()</para></listitem>
213 <listitem><para>set_irq_chip_data()</para></listitem>
214 </itemizedlist>
215 See the autogenerated function documentation for details.
216 </para>
217 </sect1>
Rob Landleyaa9128f2008-02-07 00:13:28 -0800218 <sect1 id="Highlevel_IRQ_flow_handlers">
Thomas Gleixner11c869e2006-06-29 02:24:47 -0700219 <title>Highlevel IRQ flow handlers</title>
220 <para>
221 The generic layer provides a set of pre-defined irq-flow methods:
222 <itemizedlist>
223 <listitem><para>handle_level_irq</para></listitem>
224 <listitem><para>handle_edge_irq</para></listitem>
Thomas Gleixner25ade602010-09-30 20:33:11 +0200225 <listitem><para>handle_fasteoi_irq</para></listitem>
Thomas Gleixner11c869e2006-06-29 02:24:47 -0700226 <listitem><para>handle_simple_irq</para></listitem>
227 <listitem><para>handle_percpu_irq</para></listitem>
228 </itemizedlist>
229 The interrupt flow handlers (either predefined or architecture
230 specific) are assigned to specific interrupts by the architecture
231 either during bootup or during device initialization.
232 </para>
Rob Landleyaa9128f2008-02-07 00:13:28 -0800233 <sect2 id="Default_flow_implementations">
Thomas Gleixner11c869e2006-06-29 02:24:47 -0700234 <title>Default flow implementations</title>
Rob Landleyaa9128f2008-02-07 00:13:28 -0800235 <sect3 id="Helper_functions">
Thomas Gleixner11c869e2006-06-29 02:24:47 -0700236 <title>Helper functions</title>
237 <para>
238 The helper functions call the chip primitives and
239 are used by the default flow implementations.
240 The following helper functions are implemented (simplified excerpt):
241 <programlisting>
Thomas Gleixner25ade602010-09-30 20:33:11 +0200242default_enable(struct irq_data *data)
Thomas Gleixner11c869e2006-06-29 02:24:47 -0700243{
Thomas Gleixner25ade602010-09-30 20:33:11 +0200244 desc->chip->irq_unmask(data);
Thomas Gleixner11c869e2006-06-29 02:24:47 -0700245}
246
Thomas Gleixner25ade602010-09-30 20:33:11 +0200247default_disable(struct irq_data *data)
Thomas Gleixner11c869e2006-06-29 02:24:47 -0700248{
Thomas Gleixner25ade602010-09-30 20:33:11 +0200249 if (!delay_disable(data))
250 desc->chip->irq_mask(data);
Thomas Gleixner11c869e2006-06-29 02:24:47 -0700251}
252
Thomas Gleixner25ade602010-09-30 20:33:11 +0200253default_ack(struct irq_data *data)
Thomas Gleixner11c869e2006-06-29 02:24:47 -0700254{
Thomas Gleixner25ade602010-09-30 20:33:11 +0200255 chip->irq_ack(data);
Thomas Gleixner11c869e2006-06-29 02:24:47 -0700256}
257
Thomas Gleixner25ade602010-09-30 20:33:11 +0200258default_mask_ack(struct irq_data *data)
Thomas Gleixner11c869e2006-06-29 02:24:47 -0700259{
Thomas Gleixner25ade602010-09-30 20:33:11 +0200260 if (chip->irq_mask_ack) {
261 chip->irq_mask_ack(data);
Thomas Gleixner11c869e2006-06-29 02:24:47 -0700262 } else {
Thomas Gleixner25ade602010-09-30 20:33:11 +0200263 chip->irq_mask(data);
264 chip->irq_ack(data);
Thomas Gleixner11c869e2006-06-29 02:24:47 -0700265 }
266}
267
Thomas Gleixner25ade602010-09-30 20:33:11 +0200268noop(struct irq_data *data))
Thomas Gleixner11c869e2006-06-29 02:24:47 -0700269{
270}
271
272 </programlisting>
273 </para>
274 </sect3>
275 </sect2>
Rob Landleyaa9128f2008-02-07 00:13:28 -0800276 <sect2 id="Default_flow_handler_implementations">
Thomas Gleixner11c869e2006-06-29 02:24:47 -0700277 <title>Default flow handler implementations</title>
Rob Landleyaa9128f2008-02-07 00:13:28 -0800278 <sect3 id="Default_Level_IRQ_flow_handler">
Thomas Gleixner11c869e2006-06-29 02:24:47 -0700279 <title>Default Level IRQ flow handler</title>
280 <para>
281 handle_level_irq provides a generic implementation
282 for level-triggered interrupts.
283 </para>
284 <para>
285 The following control flow is implemented (simplified excerpt):
286 <programlisting>
Thomas Gleixner25ade602010-09-30 20:33:11 +0200287desc->chip->irq_mask();
Thomas Gleixner11c869e2006-06-29 02:24:47 -0700288handle_IRQ_event(desc->action);
Thomas Gleixner25ade602010-09-30 20:33:11 +0200289desc->chip->irq_unmask();
Thomas Gleixner11c869e2006-06-29 02:24:47 -0700290 </programlisting>
291 </para>
Thomas Gleixner25ade602010-09-30 20:33:11 +0200292 </sect3>
293 <sect3 id="Default_FASTEOI_IRQ_flow_handler">
294 <title>Default Fast EOI IRQ flow handler</title>
295 <para>
296 handle_fasteoi_irq provides a generic implementation
297 for interrupts, which only need an EOI at the end of
298 the handler
299 </para>
300 <para>
301 The following control flow is implemented (simplified excerpt):
302 <programlisting>
303handle_IRQ_event(desc->action);
304desc->chip->irq_eoi();
305 </programlisting>
306 </para>
307 </sect3>
Rob Landleyaa9128f2008-02-07 00:13:28 -0800308 <sect3 id="Default_Edge_IRQ_flow_handler">
Thomas Gleixner11c869e2006-06-29 02:24:47 -0700309 <title>Default Edge IRQ flow handler</title>
310 <para>
311 handle_edge_irq provides a generic implementation
312 for edge-triggered interrupts.
313 </para>
314 <para>
315 The following control flow is implemented (simplified excerpt):
316 <programlisting>
317if (desc->status &amp; running) {
Thomas Gleixner25ade602010-09-30 20:33:11 +0200318 desc->chip->irq_mask();
Thomas Gleixner11c869e2006-06-29 02:24:47 -0700319 desc->status |= pending | masked;
320 return;
321}
Thomas Gleixner25ade602010-09-30 20:33:11 +0200322desc->chip->irq_ack();
Thomas Gleixner11c869e2006-06-29 02:24:47 -0700323desc->status |= running;
324do {
325 if (desc->status &amp; masked)
Thomas Gleixner25ade602010-09-30 20:33:11 +0200326 desc->chip->irq_unmask();
David S. Millerb06824c2006-12-12 01:00:06 -0800327 desc->status &amp;= ~pending;
Thomas Gleixner11c869e2006-06-29 02:24:47 -0700328 handle_IRQ_event(desc->action);
329} while (status &amp; pending);
David S. Millerb06824c2006-12-12 01:00:06 -0800330desc->status &amp;= ~running;
Thomas Gleixner11c869e2006-06-29 02:24:47 -0700331 </programlisting>
332 </para>
333 </sect3>
Rob Landleyaa9128f2008-02-07 00:13:28 -0800334 <sect3 id="Default_simple_IRQ_flow_handler">
Thomas Gleixner11c869e2006-06-29 02:24:47 -0700335 <title>Default simple IRQ flow handler</title>
336 <para>
337 handle_simple_irq provides a generic implementation
338 for simple interrupts.
339 </para>
340 <para>
341 Note: The simple flow handler does not call any
342 handler/chip primitives.
343 </para>
344 <para>
345 The following control flow is implemented (simplified excerpt):
346 <programlisting>
347handle_IRQ_event(desc->action);
348 </programlisting>
349 </para>
350 </sect3>
Rob Landleyaa9128f2008-02-07 00:13:28 -0800351 <sect3 id="Default_per_CPU_flow_handler">
Thomas Gleixner11c869e2006-06-29 02:24:47 -0700352 <title>Default per CPU flow handler</title>
353 <para>
354 handle_percpu_irq provides a generic implementation
355 for per CPU interrupts.
356 </para>
357 <para>
358 Per CPU interrupts are only available on SMP and
359 the handler provides a simplified version without
360 locking.
361 </para>
362 <para>
363 The following control flow is implemented (simplified excerpt):
364 <programlisting>
Thomas Gleixner11c869e2006-06-29 02:24:47 -0700365handle_IRQ_event(desc->action);
Thomas Gleixner25ade602010-09-30 20:33:11 +0200366if (desc->chip->irq_eoi)
367 desc->chip->irq_eoi();
Thomas Gleixner11c869e2006-06-29 02:24:47 -0700368 </programlisting>
369 </para>
370 </sect3>
371 </sect2>
Rob Landleyaa9128f2008-02-07 00:13:28 -0800372 <sect2 id="Quirks_and_optimizations">
Thomas Gleixner11c869e2006-06-29 02:24:47 -0700373 <title>Quirks and optimizations</title>
374 <para>
375 The generic functions are intended for 'clean' architectures and chips,
376 which have no platform-specific IRQ handling quirks. If an architecture
377 needs to implement quirks on the 'flow' level then it can do so by
378 overriding the highlevel irq-flow handler.
379 </para>
380 </sect2>
Rob Landleyaa9128f2008-02-07 00:13:28 -0800381 <sect2 id="Delayed_interrupt_disable">
Thomas Gleixner11c869e2006-06-29 02:24:47 -0700382 <title>Delayed interrupt disable</title>
383 <para>
384 This per interrupt selectable feature, which was introduced by Russell
385 King in the ARM interrupt implementation, does not mask an interrupt
386 at the hardware level when disable_irq() is called. The interrupt is
387 kept enabled and is masked in the flow handler when an interrupt event
388 happens. This prevents losing edge interrupts on hardware which does
389 not store an edge interrupt event while the interrupt is disabled at
390 the hardware level. When an interrupt arrives while the IRQ_DISABLED
391 flag is set, then the interrupt is masked at the hardware level and
392 the IRQ_PENDING bit is set. When the interrupt is re-enabled by
393 enable_irq() the pending bit is checked and if it is set, the
394 interrupt is resent either via hardware or by a software resend
395 mechanism. (It's necessary to enable CONFIG_HARDIRQS_SW_RESEND when
396 you want to use the delayed interrupt disable feature and your
397 hardware is not capable of retriggering an interrupt.)
Thomas Gleixner25ade602010-09-30 20:33:11 +0200398 The delayed interrupt disable is not configurable.
Thomas Gleixner11c869e2006-06-29 02:24:47 -0700399 </para>
400 </sect2>
401 </sect1>
Rob Landleyaa9128f2008-02-07 00:13:28 -0800402 <sect1 id="Chiplevel_hardware_encapsulation">
Thomas Gleixner11c869e2006-06-29 02:24:47 -0700403 <title>Chiplevel hardware encapsulation</title>
404 <para>
405 The chip level hardware descriptor structure irq_chip
406 contains all the direct chip relevant functions, which
407 can be utilized by the irq flow implementations.
408 <itemizedlist>
Thomas Gleixner25ade602010-09-30 20:33:11 +0200409 <listitem><para>irq_ack()</para></listitem>
410 <listitem><para>irq_mask_ack() - Optional, recommended for performance</para></listitem>
411 <listitem><para>irq_mask()</para></listitem>
412 <listitem><para>irq_unmask()</para></listitem>
413 <listitem><para>irq_retrigger() - Optional</para></listitem>
414 <listitem><para>irq_set_type() - Optional</para></listitem>
415 <listitem><para>irq_set_wake() - Optional</para></listitem>
Thomas Gleixner11c869e2006-06-29 02:24:47 -0700416 </itemizedlist>
417 These primitives are strictly intended to mean what they say: ack means
418 ACK, masking means masking of an IRQ line, etc. It is up to the flow
419 handler(s) to use these basic units of lowlevel functionality.
420 </para>
421 </sect1>
422 </chapter>
423
424 <chapter id="doirq">
425 <title>__do_IRQ entry point</title>
426 <para>
427 The original implementation __do_IRQ() is an alternative entry
428 point for all types of interrupts.
429 </para>
430 <para>
431 This handler turned out to be not suitable for all
432 interrupt hardware and was therefore reimplemented with split
433 functionality for egde/level/simple/percpu interrupts. This is not
434 only a functional optimization. It also shortens code paths for
435 interrupts.
436 </para>
437 <para>
438 To make use of the split implementation, replace the call to
Krzysztof Halasabebd04c2009-11-15 18:57:24 +0100439 __do_IRQ by a call to desc->handle_irq() and associate
440 the appropriate handler function to desc->handle_irq().
Thomas Gleixner11c869e2006-06-29 02:24:47 -0700441 In most cases the generic handler implementations should
442 be sufficient.
443 </para>
444 </chapter>
445
446 <chapter id="locking">
447 <title>Locking on SMP</title>
448 <para>
449 The locking of chip registers is up to the architecture that
450 defines the chip primitives. There is a chip->lock field that can be used
451 for serialization, but the generic layer does not touch it. The per-irq
452 structure is protected via desc->lock, by the generic layer.
453 </para>
454 </chapter>
455 <chapter id="structs">
456 <title>Structures</title>
457 <para>
458 This chapter contains the autogenerated documentation of the structures which are
459 used in the generic IRQ layer.
460 </para>
461!Iinclude/linux/irq.h
Thomas Gleixnera9d0a1a2009-03-03 16:58:16 +0100462!Iinclude/linux/interrupt.h
Thomas Gleixner11c869e2006-06-29 02:24:47 -0700463 </chapter>
464
465 <chapter id="pubfunctions">
466 <title>Public Functions Provided</title>
467 <para>
468 This chapter contains the autogenerated documentation of the kernel API functions
469 which are exported.
470 </para>
471!Ekernel/irq/manage.c
472!Ekernel/irq/chip.c
473 </chapter>
474
475 <chapter id="intfunctions">
476 <title>Internal Functions Provided</title>
477 <para>
478 This chapter contains the autogenerated documentation of the internal functions.
479 </para>
Thomas Gleixner25ade602010-09-30 20:33:11 +0200480!Ikernel/irq/irqdesc.c
Thomas Gleixner11c869e2006-06-29 02:24:47 -0700481!Ikernel/irq/handle.c
482!Ikernel/irq/chip.c
483 </chapter>
484
485 <chapter id="credits">
486 <title>Credits</title>
487 <para>
488 The following people have contributed to this document:
489 <orderedlist>
490 <listitem><para>Thomas Gleixner<email>tglx@linutronix.de</email></para></listitem>
491 <listitem><para>Ingo Molnar<email>mingo@elte.hu</email></para></listitem>
492 </orderedlist>
493 </para>
494 </chapter>
495</book>