[net-next-2.6.git] / Documentation / DocBook / genericirq.tmpl

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN"
	"http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []>

<book id="Generic-IRQ-Guide">
 <bookinfo>
  <title>Linux generic IRQ handling</title>

  <authorgroup>
   <author>
    <firstname>Thomas</firstname>
    <surname>Gleixner</surname>
    <affiliation>
     <address>
      <email>tglx@linutronix.de</email>
     </address>
    </affiliation>
   </author>
   <author>
    <firstname>Ingo</firstname>
    <surname>Molnar</surname>
    <affiliation>
     <address>
      <email>mingo@elte.hu</email>
     </address>
    </affiliation>
   </author>
  </authorgroup>

  <copyright>
   <year>2005-2010</year>
   <holder>Thomas Gleixner</holder>
  </copyright>
  <copyright>
   <year>2005-2006</year>
   <holder>Ingo Molnar</holder>
  </copyright>

  <legalnotice>
   <para>
     This documentation is free software; you can redistribute
     it and/or modify it under the terms of the GNU General Public
     License version 2 as published by the Free Software Foundation.
   </para>

   <para>
     This program is distributed in the hope that it will be
     useful, but WITHOUT ANY WARRANTY; without even the implied
     warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
     See the GNU General Public License for more details.
   </para>

   <para>
     You should have received a copy of the GNU General Public
     License along with this program; if not, write to the Free
     Software Foundation, Inc., 59 Temple Place, Suite 330, Boston,
     MA 02111-1307 USA
   </para>

   <para>
     For more details see the file COPYING in the source
     distribution of Linux.
   </para>
  </legalnotice>
 </bookinfo>

<toc></toc>

  <chapter id="intro">
    <title>Introduction</title>
    <para>
	The generic interrupt handling layer is designed to provide a
	complete abstraction of interrupt handling for device drivers.
	It is able to handle all the different types of interrupt controller
	hardware. Device drivers use generic API functions to request, enable,
	disable and free interrupts. The drivers do not have to know anything
	about interrupt hardware details, so they can be used on different
	platforms without code changes.
    </para>
    <para>
  	This documentation is provided to developers who want to implement
	an interrupt subsystem based for their architecture, with the help
	of the generic IRQ handling layer.
    </para>
  </chapter>

  <chapter id="rationale">
    <title>Rationale</title>
	<para>
	The original implementation of interrupt handling in Linux is using
	the __do_IRQ() super-handler, which is able to deal with every
	type of interrupt logic.
	</para>
	<para>
	Originally, Russell King identified different types of handlers to
	build a quite universal set for the ARM interrupt handler
	implementation in Linux 2.5/2.6. He distinguished between:
	<itemizedlist>
	  <listitem><para>Level type</para></listitem>
	  <listitem><para>Edge type</para></listitem>
	  <listitem><para>Simple type</para></listitem>
	</itemizedlist>
	During the implementation we identified another type:
	<itemizedlist>
	  <listitem><para>Fast EOI type</para></listitem>
	</itemizedlist>
	In the SMP world of the __do_IRQ() super-handler another type
	was identified:
	<itemizedlist>
	  <listitem><para>Per CPU type</para></listitem>
	</itemizedlist>
	</para>
	<para>
	This split implementation of highlevel IRQ handlers allows us to
	optimize the flow of the interrupt handling for each specific
	interrupt type. This reduces complexity in that particular codepath
	and allows the optimized handling of a given type.
	</para>
	<para>
	The original general IRQ implementation used hw_interrupt_type
	structures and their ->ack(), ->end() [etc.] callbacks to
	differentiate the flow control in the super-handler. This leads to
	a mix of flow logic and lowlevel hardware logic, and it also leads
	to unnecessary code duplication: for example in i386, there is a
	ioapic_level_irq and a ioapic_edge_irq irq-type which share many
	of the lowlevel details but have different flow handling.
	</para>
	<para>
	A more natural abstraction is the clean separation of the
	'irq flow' and the 'chip details'.
	</para>
	<para>
	Analysing a couple of architecture's IRQ subsystem implementations
	reveals that most of them can use a generic set of 'irq flow'
	methods and only need to add the chip level specific code.
	The separation is also valuable for (sub)architectures
	which need specific quirks in the irq flow itself but not in the
	chip-details - and thus provides a more transparent IRQ subsystem
	design.
	</para>
	<para>
	Each interrupt descriptor is assigned its own highlevel flow
	handler, which is normally one of the generic
	implementations. (This highlevel flow handler implementation also
	makes it simple to provide demultiplexing handlers which can be
	found in embedded platforms on various architectures.)
	</para>
	<para>
	The separation makes the generic interrupt handling layer more
	flexible and extensible. For example, an (sub)architecture can
	use a generic irq-flow implementation for 'level type' interrupts
	and add a (sub)architecture specific 'edge type' implementation.
	</para>
	<para>
	To make the transition to the new model easier and prevent the
	breakage of existing implementations, the __do_IRQ() super-handler
	is still available. This leads to a kind of duality for the time
	being. Over time the new model should be used in more and more
	architectures, as it enables smaller and cleaner IRQ subsystems.
	It's deprecated for three years now and about to be removed.
	</para>
  </chapter>
  <chapter id="bugs">
    <title>Known Bugs And Assumptions</title>
    <para>
	None (knock on wood).
    </para>
  </chapter>

  <chapter id="Abstraction">
    <title>Abstraction layers</title>
    <para>
	There are three main levels of abstraction in the interrupt code:
	<orderedlist>
	  <listitem><para>Highlevel driver API</para></listitem>
	  <listitem><para>Highlevel IRQ flow handlers</para></listitem>
	  <listitem><para>Chiplevel hardware encapsulation</para></listitem>
	</orderedlist>
    </para>
    <sect1 id="Interrupt_control_flow">
	<title>Interrupt control flow</title>
	<para>
	Each interrupt is described by an interrupt descriptor structure
	irq_desc. The interrupt is referenced by an 'unsigned int' numeric
	value which selects the corresponding interrupt decription structure
	in the descriptor structures array.
	The descriptor structure contains status information and pointers
	to the interrupt flow method and the interrupt chip structure
	which are assigned to this interrupt.
	</para>
	<para>
	Whenever an interrupt triggers, the lowlevel arch code calls into
	the generic interrupt code by calling desc->handle_irq().
	This highlevel IRQ handling function only uses desc->chip primitives
	referenced by the assigned chip descriptor structure.
	</para>
    </sect1>
    <sect1 id="Highlevel_Driver_API">
	<title>Highlevel Driver API</title>
	<para>
	  The highlevel Driver API consists of following functions:
	  <itemizedlist>
	  <listitem><para>request_irq()</para></listitem>
	  <listitem><para>free_irq()</para></listitem>
	  <listitem><para>disable_irq()</para></listitem>
	  <listitem><para>enable_irq()</para></listitem>
	  <listitem><para>disable_irq_nosync() (SMP only)</para></listitem>
	  <listitem><para>synchronize_irq() (SMP only)</para></listitem>
	  <listitem><para>set_irq_type()</para></listitem>
	  <listitem><para>set_irq_wake()</para></listitem>
	  <listitem><para>set_irq_data()</para></listitem>
	  <listitem><para>set_irq_chip()</para></listitem>
	  <listitem><para>set_irq_chip_data()</para></listitem>
          </itemizedlist>
	  See the autogenerated function documentation for details.
	</para>
    </sect1>
    <sect1 id="Highlevel_IRQ_flow_handlers">
	<title>Highlevel IRQ flow handlers</title>
	<para>
	  The generic layer provides a set of pre-defined irq-flow methods:
	  <itemizedlist>
	  <listitem><para>handle_level_irq</para></listitem>
	  <listitem><para>handle_edge_irq</para></listitem>
	  <listitem><para>handle_fasteoi_irq</para></listitem>
	  <listitem><para>handle_simple_irq</para></listitem>
	  <listitem><para>handle_percpu_irq</para></listitem>
	  </itemizedlist>
	  The interrupt flow handlers (either predefined or architecture
	  specific) are assigned to specific interrupts by the architecture
	  either during bootup or during device initialization.
	</para>
	<sect2 id="Default_flow_implementations">
	<title>Default flow implementations</title>
	    <sect3 id="Helper_functions">
	 	<title>Helper functions</title>
		<para>
		The helper functions call the chip primitives and
		are used by the default flow implementations.
		The following helper functions are implemented (simplified excerpt):
		<programlisting>
default_enable(struct irq_data *data)
{
	desc->chip->irq_unmask(data);
}

default_disable(struct irq_data *data)
{
	if (!delay_disable(data))
		desc->chip->irq_mask(data);
}

default_ack(struct irq_data *data)
{
	chip->irq_ack(data);
}

default_mask_ack(struct irq_data *data)
{
	if (chip->irq_mask_ack) {
		chip->irq_mask_ack(data);
	} else {
		chip->irq_mask(data);
		chip->irq_ack(data);
	}
}

noop(struct irq_data *data))
{
}

		</programlisting>
	        </para>
	    </sect3>
	</sect2>
	<sect2 id="Default_flow_handler_implementations">
	<title>Default flow handler implementations</title>
	    <sect3 id="Default_Level_IRQ_flow_handler">
	 	<title>Default Level IRQ flow handler</title>
		<para>
		handle_level_irq provides a generic implementation
		for level-triggered interrupts.
		</para>
		<para>
		The following control flow is implemented (simplified excerpt):
		<programlisting>
desc->chip->irq_mask();
handle_IRQ_event(desc->action);
desc->chip->irq_unmask();
		</programlisting>
		</para>
	    </sect3>
	    <sect3 id="Default_FASTEOI_IRQ_flow_handler">
		<title>Default Fast EOI IRQ flow handler</title>
		<para>
		handle_fasteoi_irq provides a generic implementation
		for interrupts, which only need an EOI at the end of
		the handler
		</para>
		<para>
		The following control flow is implemented (simplified excerpt):
		<programlisting>
handle_IRQ_event(desc->action);
desc->chip->irq_eoi();
		</programlisting>
		</para>
	    </sect3>
	    <sect3 id="Default_Edge_IRQ_flow_handler">
	 	<title>Default Edge IRQ flow handler</title>
		<para>
		handle_edge_irq provides a generic implementation
		for edge-triggered interrupts.
		</para>
		<para>
		The following control flow is implemented (simplified excerpt):
		<programlisting>
if (desc->status &amp; running) {
	desc->chip->irq_mask();
	desc->status |= pending | masked;
	return;
}
desc->chip->irq_ack();
desc->status |= running;
do {
	if (desc->status &amp; masked)
		desc->chip->irq_unmask();
	desc->status &amp;= ~pending;
	handle_IRQ_event(desc->action);
} while (status &amp; pending);
desc->status &amp;= ~running;
		</programlisting>
		</para>
   	    </sect3>
	    <sect3 id="Default_simple_IRQ_flow_handler">
	 	<title>Default simple IRQ flow handler</title>
		<para>
		handle_simple_irq provides a generic implementation
		for simple interrupts.
		</para>
		<para>
		Note: The simple flow handler does not call any
		handler/chip primitives.
		</para>
		<para>
		The following control flow is implemented (simplified excerpt):
		<programlisting>
handle_IRQ_event(desc->action);
		</programlisting>
		</para>
   	    </sect3>
	    <sect3 id="Default_per_CPU_flow_handler">
	 	<title>Default per CPU flow handler</title>
		<para>
		handle_percpu_irq provides a generic implementation
		for per CPU interrupts.
		</para>
		<para>
		Per CPU interrupts are only available on SMP and
		the handler provides a simplified version without
		locking.
		</para>
		<para>
		The following control flow is implemented (simplified excerpt):
		<programlisting>
handle_IRQ_event(desc->action);
if (desc->chip->irq_eoi)
        desc->chip->irq_eoi();
		</programlisting>
		</para>
   	    </sect3>
	</sect2>
	<sect2 id="Quirks_and_optimizations">
	<title>Quirks and optimizations</title>
	<para>
	The generic functions are intended for 'clean' architectures and chips,
	which have no platform-specific IRQ handling quirks. If an architecture
	needs to implement quirks on the 'flow' level then it can do so by
	overriding the highlevel irq-flow handler.
	</para>
	</sect2>
	<sect2 id="Delayed_interrupt_disable">
	<title>Delayed interrupt disable</title>
	<para>
	This per interrupt selectable feature, which was introduced by Russell
	King in the ARM interrupt implementation, does not mask an interrupt
	at the hardware level when disable_irq() is called. The interrupt is
	kept enabled and is masked in the flow handler when an interrupt event
	happens. This prevents losing edge interrupts on hardware which does
	not store an edge interrupt event while the interrupt is disabled at
	the hardware level. When an interrupt arrives while the IRQ_DISABLED
	flag is set, then the interrupt is masked at the hardware level and
	the IRQ_PENDING bit is set. When the interrupt is re-enabled by
	enable_irq() the pending bit is checked and if it is set, the
	interrupt is resent either via hardware or by a software resend
	mechanism. (It's necessary to enable CONFIG_HARDIRQS_SW_RESEND when
	you want to use the delayed interrupt disable feature and your
	hardware is not capable of retriggering	an interrupt.)
	The delayed interrupt disable is not configurable.
	</para>
	</sect2>
    </sect1>
    <sect1 id="Chiplevel_hardware_encapsulation">
	<title>Chiplevel hardware encapsulation</title>
	<para>
	The chip level hardware descriptor structure irq_chip
	contains all the direct chip relevant functions, which
	can be utilized by the irq flow implementations.
	  <itemizedlist>
	  <listitem><para>irq_ack()</para></listitem>
	  <listitem><para>irq_mask_ack() - Optional, recommended for performance</para></listitem>
	  <listitem><para>irq_mask()</para></listitem>
	  <listitem><para>irq_unmask()</para></listitem>
	  <listitem><para>irq_retrigger() - Optional</para></listitem>
	  <listitem><para>irq_set_type() - Optional</para></listitem>
	  <listitem><para>irq_set_wake() - Optional</para></listitem>
	  </itemizedlist>
	These primitives are strictly intended to mean what they say: ack means
	ACK, masking means masking of an IRQ line, etc. It is up to the flow
	handler(s) to use these basic units of lowlevel functionality.
	</para>
    </sect1>
  </chapter>

  <chapter id="doirq">
     <title>__do_IRQ entry point</title>
     <para>
 	The original implementation __do_IRQ() is an alternative entry
	point for all types of interrupts.
     </para>
     <para>
	This handler turned out to be not suitable for all
	interrupt hardware and was therefore reimplemented with split
	functionality for egde/level/simple/percpu interrupts. This is not
	only a functional optimization. It also shortens code paths for
	interrupts.
      </para>
      <para>
	To make use of the split implementation, replace the call to
	__do_IRQ by a call to desc->handle_irq() and associate
        the appropriate handler function to desc->handle_irq().
	In most cases the generic handler implementations should
	be sufficient.
     </para>
  </chapter>

  <chapter id="locking">
     <title>Locking on SMP</title>
     <para>
	The locking of chip registers is up to the architecture that
	defines the chip primitives. There is a chip->lock field that can be used
	for serialization, but the generic layer does not touch it. The per-irq
	structure is protected via desc->lock, by the generic layer.
     </para>
  </chapter>
  <chapter id="structs">
     <title>Structures</title>
     <para>
     This chapter contains the autogenerated documentation of the structures which are
     used in the generic IRQ layer.
     </para>
!Iinclude/linux/irq.h
!Iinclude/linux/interrupt.h
  </chapter>

  <chapter id="pubfunctions">
     <title>Public Functions Provided</title>
     <para>
     This chapter contains the autogenerated documentation of the kernel API functions
      which are exported.
     </para>
!Ekernel/irq/manage.c
!Ekernel/irq/chip.c
  </chapter>

  <chapter id="intfunctions">
     <title>Internal Functions Provided</title>
     <para>
     This chapter contains the autogenerated documentation of the internal functions.
     </para>
!Ikernel/irq/irqdesc.c
!Ikernel/irq/handle.c
!Ikernel/irq/chip.c
  </chapter>

  <chapter id="credits">
     <title>Credits</title>
	<para>
		The following people have contributed to this document:
		<orderedlist>
			<listitem><para>Thomas Gleixner<email>tglx@linutronix.de</email></para></listitem>
			<listitem><para>Ingo Molnar<email>mingo@elte.hu</email></para></listitem>
		</orderedlist>
	</para>
  </chapter>
</book>
Commit	Line	Data
11c869ea TG	1	<?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>
25ade601	31	<year>2005-2010</year>
11c869ea TG	32	<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>
25ade601 TG	103	During the implementation we identified another type:
	104	<itemizedlist>
	105	<listitem><para>Fast EOI type</para></listitem>
	106	</itemizedlist>
11c869ea TG	107	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.
25ade601	160	It's deprecated for three years now and about to be removed.
11c869ea TG	161	</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>
aa9128f3	180	<sect1 id="Interrupt_control_flow">
11c869ea TG	181	<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>
aa9128f3	198	<sect1 id="Highlevel_Driver_API">
11c869ea TG	199	<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>
aa9128f3	218	<sect1 id="Highlevel_IRQ_flow_handlers">
11c869ea TG	219	<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>
25ade601	225	<listitem><para>handle_fasteoi_irq</para></listitem>
11c869ea TG	226	<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>
aa9128f3	233	<sect2 id="Default_flow_implementations">
11c869ea	234	<title>Default flow implementations</title>
aa9128f3	235	<sect3 id="Helper_functions">
11c869ea TG	236	<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>
25ade601	242	default_enable(struct irq_data *data)
11c869ea	243	{
25ade601	244	desc->chip->irq_unmask(data);
11c869ea TG	245	}
11c869ea TG	246
25ade601	247	default_disable(struct irq_data *data)
11c869ea	248	{
25ade601 TG	249	if (!delay_disable(data))
25ade601 TG	250	desc->chip->irq_mask(data);
11c869ea TG	251	}
11c869ea TG	252
25ade601	253	default_ack(struct irq_data *data)
11c869ea	254	{
25ade601	255	chip->irq_ack(data);
11c869ea TG	256	}
11c869ea TG	257
25ade601	258	default_mask_ack(struct irq_data *data)
11c869ea	259	{
25ade601 TG	260	if (chip->irq_mask_ack) {
25ade601 TG	261	chip->irq_mask_ack(data);
11c869ea	262	} else {
25ade601 TG	263	chip->irq_mask(data);
25ade601 TG	264	chip->irq_ack(data);
11c869ea TG	265	}
	266	}
	267
25ade601	268	noop(struct irq_data *data))
11c869ea TG	269	{
	270	}
	271
	272	</programlisting>
	273	</para>
	274	</sect3>
	275	</sect2>
aa9128f3	276	<sect2 id="Default_flow_handler_implementations">
11c869ea	277	<title>Default flow handler implementations</title>
aa9128f3	278	<sect3 id="Default_Level_IRQ_flow_handler">
11c869ea TG	279	<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>
25ade601	287	desc->chip->irq_mask();
11c869ea	288	handle_IRQ_event(desc->action);
25ade601	289	desc->chip->irq_unmask();
11c869ea TG	290	</programlisting>
11c869ea TG	291	</para>
25ade601 TG	292	</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>
	303	handle_IRQ_event(desc->action);
	304	desc->chip->irq_eoi();
	305	</programlisting>
	306	</para>
	307	</sect3>
aa9128f3	308	<sect3 id="Default_Edge_IRQ_flow_handler">
11c869ea TG	309	<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>
	317	if (desc->status & running) {
25ade601	318	desc->chip->irq_mask();
11c869ea TG	319	desc->status \|= pending \| masked;
	320	return;
	321	}
25ade601	322	desc->chip->irq_ack();
11c869ea TG	323	desc->status \|= running;
	324	do {
	325	if (desc->status & masked)
25ade601	326	desc->chip->irq_unmask();
b06824ce	327	desc->status &= ~pending;
11c869ea TG	328	handle_IRQ_event(desc->action);
11c869ea TG	329	} while (status & pending);
b06824ce	330	desc->status &= ~running;
11c869ea TG	331	</programlisting>
	332	</para>
	333	</sect3>
aa9128f3	334	<sect3 id="Default_simple_IRQ_flow_handler">
11c869ea TG	335	<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>
	347	handle_IRQ_event(desc->action);
	348	</programlisting>
	349	</para>
	350	</sect3>
aa9128f3	351	<sect3 id="Default_per_CPU_flow_handler">
11c869ea TG	352	<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>
11c869ea	365	handle_IRQ_event(desc->action);
25ade601 TG	366	if (desc->chip->irq_eoi)
25ade601 TG	367	desc->chip->irq_eoi();
11c869ea TG	368	</programlisting>
	369	</para>
	370	</sect3>
	371	</sect2>
aa9128f3	372	<sect2 id="Quirks_and_optimizations">
11c869ea TG	373	<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>
aa9128f3	381	<sect2 id="Delayed_interrupt_disable">
11c869ea TG	382	<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.)
25ade601	398	The delayed interrupt disable is not configurable.
11c869ea TG	399	</para>
	400	</sect2>
	401	</sect1>
aa9128f3	402	<sect1 id="Chiplevel_hardware_encapsulation">
11c869ea TG	403	<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>
25ade601 TG	409	<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>
11c869ea TG	416	</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
bebd04cc KH	439	__do_IRQ by a call to desc->handle_irq() and associate
bebd04cc KH	440	the appropriate handler function to desc->handle_irq().
11c869ea TG	441	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
a9d0a1a3	462	!Iinclude/linux/interrupt.h
11c869ea TG	463	</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>
25ade601	480	!Ikernel/irq/irqdesc.c
11c869ea TG	481	!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>