<chapter id="rationale">
<title>Rationale</title>
<para>
- The original implementation of interrupt handling in Linux is using
+ 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>
</itemizedlist>
</para>
<para>
- This split implementation of highlevel IRQ handlers allows us to
+ 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 codepath
+ 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 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.
+ 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
<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.
+ 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
+ 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
+ Each interrupt descriptor is assigned its own high-level flow
handler, which is normally one of the generic
- implementations. (This highlevel flow handler implementation also
+ 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
+ use a generic IRQ-flow implementation for 'level type' interrupts
and add a (sub)architecture specific 'edge type' implementation.
</para>
<para>
<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>
+ <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">
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
+ 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>Highlevel Driver API</title>
+ <title>High-level Driver API</title>
<para>
- The highlevel Driver API consists of following functions:
+ The high-level Driver API consists of following functions:
<itemizedlist>
<listitem><para>request_irq()</para></listitem>
<listitem><para>free_irq()</para></listitem>
</para>
</sect1>
<sect1 id="Highlevel_IRQ_flow_handlers">
- <title>Highlevel IRQ flow handlers</title>
+ <title>High-level IRQ flow handlers</title>
<para>
The generic layer provides a set of pre-defined irq-flow methods:
<itemizedlist>
<listitem><para>handle_edge_eoi_irq</para></listitem>
<listitem><para>handle_bad_irq</para></listitem>
</itemizedlist>
- The interrupt flow handlers (either predefined or architecture
+ 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>
<para>
handle_fasteoi_irq provides a generic implementation
for interrupts, which only need an EOI at the end of
- the handler
+ the handler.
</para>
<para>
The following control flow is implemented (simplified excerpt):
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.
+ overriding the high-level irq-flow handler.
</para>
</sect2>
<sect2 id="Delayed_interrupt_disable">
</sect2>
</sect1>
<sect1 id="Chiplevel_hardware_encapsulation">
- <title>Chiplevel hardware encapsulation</title>
+ <title>Chip-level hardware encapsulation</title>
<para>
- The chip level hardware descriptor structure irq_chip
+ 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_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_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.
+ handler(s) to use these basic units of low-level functionality.
</para>
</sect1>
</chapter>
<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.
+ point for all types of interrupts. It no longer exists.
</para>
<para>
This handler turned out to be not suitable for all
<chapter id="genericchip">
<title>Generic interrupt chip</title>
<para>
- To avoid copies of identical implementations of irq chips the
+ 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 different themself.
+ functionality slightly differently themselves.
</para>
!Ekernel/irq/generic-chip.c
</chapter>
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