diff options
Diffstat (limited to 'Documentation/DocBook')
| -rw-r--r-- | Documentation/DocBook/Makefile | 3 | ||||
| -rw-r--r-- | Documentation/DocBook/genericirq.tmpl | 474 | ||||
| -rw-r--r-- | Documentation/DocBook/kernel-locking.tmpl | 2 |
3 files changed, 477 insertions, 2 deletions
diff --git a/Documentation/DocBook/Makefile b/Documentation/DocBook/Makefile index 5a2882d275ba..66e1cf733571 100644 --- a/Documentation/DocBook/Makefile +++ b/Documentation/DocBook/Makefile @@ -10,7 +10,8 @@ DOCBOOKS := wanbook.xml z8530book.xml mcabook.xml videobook.xml \ kernel-hacking.xml kernel-locking.xml deviceiobook.xml \ procfs-guide.xml writing_usb_driver.xml \ kernel-api.xml journal-api.xml lsm.xml usb.xml \ - gadget.xml libata.xml mtdnand.xml librs.xml rapidio.xml + gadget.xml libata.xml mtdnand.xml librs.xml rapidio.xml \ + genericirq.xml ### # The build process is as follows (targets): diff --git a/Documentation/DocBook/genericirq.tmpl b/Documentation/DocBook/genericirq.tmpl new file mode 100644 index 000000000000..0f4a4b6321e4 --- /dev/null +++ b/Documentation/DocBook/genericirq.tmpl @@ -0,0 +1,474 @@ +<?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>2005-2006</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); +} + +default_disable(irq) +{ + if (!delay_disable(irq)) + desc->chip->mask(irq); +} + +default_ack(irq) +{ + chip->ack(irq); +} + +default_mask_ack(irq) +{ + if (chip->mask_ack) { + chip->mask_ack(irq); + } else { + chip->mask(irq); + chip->ack(irq); + } +} + +noop(irq) +{ +} + + </programlisting> + </para> + </sect3> + </sect2> + <sect2> + <title>Default flow handler implementations</title> + <sect3> + <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->start(); +handle_IRQ_event(desc->action); +desc->chip->end(); + </programlisting> + </para> + </sect3> + <sect3> + <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->chip->hold(); + desc->status |= pending | masked; + return; +} +desc->chip->start(); +desc->status |= running; +do { + if (desc->status & masked) + desc->chip->enable(); + desc-status &= ~pending; + handle_IRQ_event(desc->action); +} while (status & pending); +desc-status &= ~running; +desc->chip->end(); + </programlisting> + </para> + </sect3> + <sect3> + <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> + <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> +desc->chip->start(); +handle_IRQ_event(desc->action); +desc->chip->end(); + </programlisting> + </para> + </sect3> + </sect2> + <sect2> + <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> + <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 can be runtime enabled, per interrupt, + by setting the IRQ_DELAYED_DISABLE flag in the irq_desc status field. + </para> + </sect2> + </sect1> + <sect1> + <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>ack()</para></listitem> + <listitem><para>mask_ack() - Optional, recommended for performance</para></listitem> + <listitem><para>mask()</para></listitem> + <listitem><para>unmask()</para></listitem> + <listitem><para>retrigger() - Optional</para></listitem> + <listitem><para>set_type() - Optional</para></listitem> + <listitem><para>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->chip->handle_irq() and associate + the appropriate handler function to desc->chip->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 + </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/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> diff --git a/Documentation/DocBook/kernel-locking.tmpl b/Documentation/DocBook/kernel-locking.tmpl index 158ffe9bfade..644c3884fab9 100644 --- a/Documentation/DocBook/kernel-locking.tmpl +++ b/Documentation/DocBook/kernel-locking.tmpl @@ -1590,7 +1590,7 @@ the amount of locking which needs to be done. <para> Our final dilemma is this: when can we actually destroy the removed element? Remember, a reader might be stepping through - this element in the list right now: it we free this element and + this element in the list right now: if we free this element and the <symbol>next</symbol> pointer changes, the reader will jump off into garbage and crash. We need to wait until we know that all the readers who were traversing the list when we deleted the |
