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-<?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->irq_data.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>irq_set_irq_type()</para></listitem>
- <listitem><para>irq_set_irq_wake()</para></listitem>
- <listitem><para>irq_set_handler_data()</para></listitem>
- <listitem><para>irq_set_chip()</para></listitem>
- <listitem><para>irq_set_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>
- <listitem><para>handle_edge_eoi_irq</para></listitem>
- <listitem><para>handle_bad_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->irq_data.chip->irq_unmask(data);
-}
-
-default_disable(struct irq_data *data)
-{
- if (!delay_disable(data))
- desc->irq_data.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->irq_data.chip->irq_mask_ack();
-handle_irq_event(desc->action);
-desc->irq_data.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->irq_data.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->irq_data.chip->irq_mask_ack();
- desc->status |= pending | masked;
- return;
-}
-desc->irq_data.chip->irq_ack();
-desc->status |= running;
-do {
- if (desc->status &amp; masked)
- desc->irq_data.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>
-if (desc->irq_data.chip->irq_ack)
- desc->irq_data.chip->irq_ack();
-handle_irq_event(desc->action);
-if (desc->irq_data.chip->irq_eoi)
- desc->irq_data.chip->irq_eoi();
- </programlisting>
- </para>
- </sect3>
- <sect3 id="EOI_Edge_IRQ_flow_handler">
- <title>EOI Edge IRQ flow handler</title>
- <para>
- handle_edge_eoi_irq provides an abnomination of the edge
- handler which is solely used to tame a badly wreckaged
- irq controller on powerpc/cell.
- </para>
- </sect3>
- <sect3 id="BAD_IRQ_flow_handler">
- <title>Bad IRQ flow handler</title>
- <para>
- handle_bad_irq is used for spurious interrupts which
- have no real handler assigned..
- </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_eoi() - Optional, required for eoi flow handlers</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() was an alternative entry
- point for all types of interrupts. It not longer exists.
- </para>
- <para>
- This handler turned out to be not suitable for all
- interrupt hardware and was therefore reimplemented with split
- functionality for edge/level/simple/percpu interrupts. This is not
- only a functional optimization. It also shortens code paths for
- interrupts.
- </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. 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>