521 lines
17 KiB
XML
521 lines
17 KiB
XML
<?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 uses
|
|
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 high-level IRQ handlers allows us to
|
|
optimize the flow of the interrupt handling for each specific
|
|
interrupt type. This reduces complexity in that particular code path
|
|
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 low-level hardware logic, and it also leads
|
|
to unnecessary code duplication: for example in i386, there is an
|
|
ioapic_level_irq and an ioapic_edge_irq IRQ-type which share many
|
|
of the low-level 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 high-level flow
|
|
handler, which is normally one of the generic
|
|
implementations. (This high-level 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>High-level driver API</para></listitem>
|
|
<listitem><para>High-level IRQ flow handlers</para></listitem>
|
|
<listitem><para>Chip-level 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 low-level architecture code calls
|
|
into the generic interrupt code by calling desc->handle_irq().
|
|
This high-level 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>High-level Driver API</title>
|
|
<para>
|
|
The high-level 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>High-level 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 pre-defined 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 & 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 & masked)
|
|
desc->irq_data.chip->irq_unmask();
|
|
desc->status &= ~pending;
|
|
handle_irq_event(desc->action);
|
|
} while (status & pending);
|
|
desc->status &= ~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 high-level 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>Chip-level 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 low-level 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 no 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="genericchip">
|
|
<title>Generic interrupt chip</title>
|
|
<para>
|
|
To avoid copies of identical implementations of IRQ chips the
|
|
core provides a configurable generic interrupt chip
|
|
implementation. Developers should check carefuly whether the
|
|
generic chip fits their needs before implementing the same
|
|
functionality slightly differently themselves.
|
|
</para>
|
|
!Ekernel/irq/generic-chip.c
|
|
</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>
|