Commit 1642a1e6 authored by Mauro Carvalho Chehab's avatar Mauro Carvalho Chehab Committed by Jonathan Corbet

IRQ-domain.txt: standardize document format

Each text file under Documentation follows a different
format. Some doesn't even have titles!

Change its representation to follow the adopted standard,
using ReST markups for it to be parseable by Sphinx:

- use proper markups for titles;
- mark literal blocks as such;
- add blank lines where needed.
Signed-off-by: default avatarMauro Carvalho Chehab <mchehab@s-opensource.com>
Signed-off-by: default avatarJonathan Corbet <corbet@lwn.net>
parent ae2f26aa
irq_domain interrupt number mapping library
===============================================
The irq_domain interrupt number mapping library
===============================================
The current design of the Linux kernel uses a single large number
space where each separate IRQ source is assigned a different number.
......@@ -36,7 +38,9 @@ irq_domain also implements translation from an abstract irq_fwspec
structure to hwirq numbers (Device Tree and ACPI GSI so far), and can
be easily extended to support other IRQ topology data sources.
=== irq_domain usage ===
irq_domain usage
================
An interrupt controller driver creates and registers an irq_domain by
calling one of the irq_domain_add_*() functions (each mapping method
has a different allocator function, more on that later). The function
......@@ -62,15 +66,21 @@ If the driver has the Linux IRQ number or the irq_data pointer, and
needs to know the associated hwirq number (such as in the irq_chip
callbacks) then it can be directly obtained from irq_data->hwirq.
=== Types of irq_domain mappings ===
Types of irq_domain mappings
============================
There are several mechanisms available for reverse mapping from hwirq
to Linux irq, and each mechanism uses a different allocation function.
Which reverse map type should be used depends on the use case. Each
of the reverse map types are described below:
==== Linear ====
irq_domain_add_linear()
irq_domain_create_linear()
Linear
------
::
irq_domain_add_linear()
irq_domain_create_linear()
The linear reverse map maintains a fixed size table indexed by the
hwirq number. When a hwirq is mapped, an irq_desc is allocated for
......@@ -89,9 +99,13 @@ accepts a more general abstraction 'struct fwnode_handle'.
The majority of drivers should use the linear map.
==== Tree ====
irq_domain_add_tree()
irq_domain_create_tree()
Tree
----
::
irq_domain_add_tree()
irq_domain_create_tree()
The irq_domain maintains a radix tree map from hwirq numbers to Linux
IRQs. When an hwirq is mapped, an irq_desc is allocated and the
......@@ -109,8 +123,12 @@ accepts a more general abstraction 'struct fwnode_handle'.
Very few drivers should need this mapping.
==== No Map ===-
irq_domain_add_nomap()
No Map
------
::
irq_domain_add_nomap()
The No Map mapping is to be used when the hwirq number is
programmable in the hardware. In this case it is best to program the
......@@ -121,10 +139,14 @@ Linux IRQ number into the hardware.
Most drivers cannot use this mapping.
==== Legacy ====
irq_domain_add_simple()
irq_domain_add_legacy()
irq_domain_add_legacy_isa()
Legacy
------
::
irq_domain_add_simple()
irq_domain_add_legacy()
irq_domain_add_legacy_isa()
The Legacy mapping is a special case for drivers that already have a
range of irq_descs allocated for the hwirqs. It is used when the
......@@ -163,14 +185,17 @@ that the driver using the simple domain call irq_create_mapping()
before any irq_find_mapping() since the latter will actually work
for the static IRQ assignment case.
==== Hierarchy IRQ domain ====
Hierarchy IRQ domain
--------------------
On some architectures, there may be multiple interrupt controllers
involved in delivering an interrupt from the device to the target CPU.
Let's look at a typical interrupt delivering path on x86 platforms:
Let's look at a typical interrupt delivering path on x86 platforms::
Device --> IOAPIC -> Interrupt remapping Controller -> Local APIC -> CPU
Device --> IOAPIC -> Interrupt remapping Controller -> Local APIC -> CPU
There are three interrupt controllers involved:
1) IOAPIC controller
2) Interrupt remapping controller
3) Local APIC controller
......@@ -180,7 +205,8 @@ hardware architecture, an irq_domain data structure is built for each
interrupt controller and those irq_domains are organized into hierarchy.
When building irq_domain hierarchy, the irq_domain near to the device is
child and the irq_domain near to CPU is parent. So a hierarchy structure
as below will be built for the example above.
as below will be built for the example above::
CPU Vector irq_domain (root irq_domain to manage CPU vectors)
^
|
......@@ -190,6 +216,7 @@ as below will be built for the example above.
IOAPIC irq_domain (manage IOAPIC delivery entries/pins)
There are four major interfaces to use hierarchy irq_domain:
1) irq_domain_alloc_irqs(): allocate IRQ descriptors and interrupt
controller related resources to deliver these interrupts.
2) irq_domain_free_irqs(): free IRQ descriptors and interrupt controller
......@@ -199,7 +226,8 @@ There are four major interfaces to use hierarchy irq_domain:
4) irq_domain_deactivate_irq(): deactivate interrupt controller hardware
to stop delivering the interrupt.
Following changes are needed to support hierarchy irq_domain.
Following changes are needed to support hierarchy irq_domain:
1) a new field 'parent' is added to struct irq_domain; it's used to
maintain irq_domain hierarchy information.
2) a new field 'parent_data' is added to struct irq_data; it's used to
......@@ -223,6 +251,7 @@ software architecture.
For an interrupt controller driver to support hierarchy irq_domain, it
needs to:
1) Implement irq_domain_ops.alloc and irq_domain_ops.free
2) Optionally implement irq_domain_ops.activate and
irq_domain_ops.deactivate.
......
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