genericirq.tmpl

linux 内核源代码

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

  <authorgroup>
   <author>
    <firstname>Thomas</firstname>
    <surname>Gleixner</surname>
    <affiliation>
     <address>
      <email>[e-mail]</email>
     </address>
    </affiliation>
   </author>
   <author>
    <firstname>Ingo</firstname>
    <surname>Molnar</surname>
    <affiliation>
     <address>
      <email>[e-mail]</email>
     </address>
    </affiliation>
   </author>
  </authorgroup>

  <copyright>
   <year>2005-2006</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>
	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.
	</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>
	<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>
	<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>
	<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_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>
	<title>Default flow implementations</title>
	    <sect3>
	 	<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(irq)
{
	desc->chip->unmask(irq);