# Linux generic IRQ handling

Thomas
Gleixner

          tglx@linutronix.de

Ingo
Molnar

          mingo@elte.hu

2005-2010
Thomas Gleixner
2005-2006
Ingo Molnar

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.

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.

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

For more details see the file COPYING in the source distribution of Linux.

## Introduction

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.

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.

## Rationale

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.

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:

- Level type

- Edge type

- Simple type

During the implementation we identified another type:

- Fast EOI type

In the SMP world of the __do_IRQ() super-handler another type was identified:

- Per CPU type

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.

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.

A more natural abstraction is the clean separation of the 'irq flow' and the 'chip details'.

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.

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.)

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.

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.

## Known Bugs And Assumptions

None (knock on wood).

## Abstraction layers

There are three main levels of abstraction in the interrupt code:

1. High-level driver API

2. High-level IRQ flow handlers

3. Chip-level hardware encapsulation

### Interrupt control flow

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.

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.

### High-level Driver API

The high-level Driver API consists of following functions:

- request_irq()

- free_irq()

- disable_irq()

- enable_irq()

- disable_irq_nosync() (SMP only)

- synchronize_irq() (SMP only)

- irq_set_irq_type()

- irq_set_irq_wake()

- irq_set_handler_data()

- irq_set_chip()

- irq_set_chip_data()

See the autogenerated function documentation for details.

### High-level IRQ flow handlers

The generic layer provides a set of pre-defined irq-flow methods:

- handle_level_irq

- handle_edge_irq

- handle_fasteoi_irq

- handle_simple_irq

- handle_percpu_irq

- handle_edge_eoi_irq

- handle_bad_irq

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.

#### Default flow implementations

##### Helper functions

The helper functions call the chip primitives and are used by the default flow implementations. The following helper functions are implemented (simplified excerpt):

    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))
    {
    }

#### Default flow handler implementations

##### Default Level IRQ flow handler

handle_level_irq provides a generic implementation for level-triggered interrupts.

The following control flow is implemented (simplified excerpt):

    desc->irq_data.chip->irq_mask_ack();
    handle_irq_event(desc->action);
    desc->irq_data.chip->irq_unmask();

##### Default Fast EOI IRQ flow handler

handle_fasteoi_irq provides a generic implementation for interrupts, which only need an EOI at the end of the handler.

The following control flow is implemented (simplified excerpt):

    handle_irq_event(desc->action);
    desc->irq_data.chip->irq_eoi();

##### Default Edge IRQ flow handler

handle_edge_irq provides a generic implementation for edge-triggered interrupts.

The following control flow is implemented (simplified excerpt):

    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;

##### Default simple IRQ flow handler

handle_simple_irq provides a generic implementation for simple interrupts.

Note: The simple flow handler does not call any handler/chip primitives.

The following control flow is implemented (simplified excerpt):

    handle_irq_event(desc->action);

##### Default per CPU flow handler

handle_percpu_irq provides a generic implementation for per CPU interrupts.

Per CPU interrupts are only available on SMP and the handler provides a simplified version without locking.

The following control flow is implemented (simplified excerpt):

    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();

##### EOI Edge IRQ flow handler

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.

##### Bad IRQ flow handler

handle_bad_irq is used for spurious interrupts which have no real handler assigned..

#### Quirks and optimizations

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.

#### Delayed interrupt disable

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.

### Chip-level hardware encapsulation

The chip-level hardware descriptor structure irq_chip contains all the direct chip relevant functions, which can be utilized by the irq flow implementations.

- irq_ack()

- irq_mask_ack() - Optional, recommended for performance

- irq_mask()

- irq_unmask()

- irq_eoi() - Optional, required for EOI flow handlers

- irq_retrigger() - Optional

- irq_set_type() - Optional

- irq_set_wake() - Optional

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.

## __do_IRQ entry point

The original implementation __do_IRQ() was an alternative entry point for all types of interrupts. It no longer exists.

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.

## Locking on SMP

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.

## Generic interrupt chip

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.

### LINUX

Kernel Hackers Manual March 2018
irq_gc_mask_set_bit
9
3.13.0-144-

### irq_gc_mask_set_bit

Mask chip via setting bit in mask register

#### Synopsis

       void irq_gc_mask_set_bit
       struct irq_data * d

#### Arguments

`d`

  irq_data

#### Description

Chip has a single mask register. Values of this register are cached and protected by gc->lock

### LINUX

Kernel Hackers Manual March 2018
irq_gc_mask_clr_bit
9
3.13.0-144-

### irq_gc_mask_clr_bit

Mask chip via clearing bit in mask register

#### Synopsis

       void irq_gc_mask_clr_bit
       struct irq_data * d

#### Arguments

`d`

  irq_data

#### Description

Chip has a single mask register. Values of this register are cached and protected by gc->lock

### LINUX

Kernel Hackers Manual March 2018
irq_gc_ack_set_bit
9
3.13.0-144-

### irq_gc_ack_set_bit

Ack pending interrupt via setting bit

#### Synopsis

       void irq_gc_ack_set_bit
       struct irq_data * d

#### Arguments

`d`

  irq_data

### LINUX

Kernel Hackers Manual March 2018
irq_alloc_generic_chip
9
3.13.0-144-

### irq_alloc_generic_chip

Allocate a generic chip and initialize it

#### Synopsis

       struct irq_chip_generic * irq_alloc_generic_chip
       const char * name
       int num_ct
       unsigned int irq_base
       void __iomem * reg_base
       irq_flow_handler_t handler

#### Arguments

`name`

  Name of the irq chip

`num_ct`

  Number of irq_chip_type instances associated with this

`irq_base`

  Interrupt base nr for this chip

`reg_base`

  Register base address (virtual)

`handler`

  Default flow handler associated with this chip

#### Description

Returns an initialized irq_chip_generic structure. The chip defaults to the primary (index 0) irq_chip_type and `handler`

### LINUX

Kernel Hackers Manual March 2018
irq_alloc_domain_generic_chips
9
3.13.0-144-

### irq_alloc_domain_generic_chips

Allocate generic chips for an irq domain

#### Synopsis

       int irq_alloc_domain_generic_chips
       struct irq_domain * d
       int irqs_per_chip
       int num_ct
       const char * name
       irq_flow_handler_t handler
       unsigned int clr
       unsigned int set
       enum irq_gc_flags gcflags

#### Arguments

`d`

  irq domain for which to allocate chips

`irqs_per_chip`

  Number of interrupts each chip handles

`num_ct`

  Number of irq_chip_type instances associated with this

`name`

  Name of the irq chip

`handler`

  Default flow handler associated with these chips

`clr`

  IRQ_* bits to clear in the mapping function

`set`

  IRQ_* bits to set in the mapping function

`gcflags`

  Generic chip specific setup flags

### LINUX

Kernel Hackers Manual March 2018
irq_get_domain_generic_chip
9
3.13.0-144-

### irq_get_domain_generic_chip

Get a pointer to the generic chip of a hw_irq

#### Synopsis

       struct irq_chip_generic * irq_get_domain_generic_chip
       struct irq_domain * d
       unsigned int hw_irq

#### Arguments

`d`

  irq domain pointer

`hw_irq`

  Hardware interrupt number

### LINUX

Kernel Hackers Manual March 2018
irq_setup_generic_chip
9
3.13.0-144-

### irq_setup_generic_chip

Setup a range of interrupts with a generic chip

#### Synopsis

       void irq_setup_generic_chip
       struct irq_chip_generic * gc
       u32 msk
       enum irq_gc_flags flags
       unsigned int clr
       unsigned int set

#### Arguments

`gc`

  Generic irq chip holding all data

`msk`

  Bitmask holding the irqs to initialize relative to gc->irq_base

`flags`

  Flags for initialization

`clr`

  IRQ_* bits to clear

`set`

  IRQ_* bits to set

#### Description

Set up max. 32 interrupts starting from gc->irq_base. Note, this initializes all interrupts to the primary irq_chip_type and its associated handler.

### LINUX

Kernel Hackers Manual March 2018
irq_setup_alt_chip
9
3.13.0-144-

### irq_setup_alt_chip

Switch to alternative chip

#### Synopsis

       int irq_setup_alt_chip
       struct irq_data * d
       unsigned int type

#### Arguments

`d`

  irq_data for this interrupt

`type`

  Flow type to be initialized

#### Description

Only to be called from chip->`irq_set_type` callbacks.

### LINUX

Kernel Hackers Manual March 2018
irq_remove_generic_chip
9
3.13.0-144-

### irq_remove_generic_chip

Remove a chip

#### Synopsis

       void irq_remove_generic_chip
       struct irq_chip_generic * gc
       u32 msk
       unsigned int clr
       unsigned int set

#### Arguments

`gc`

  Generic irq chip holding all data

`msk`

  Bitmask holding the irqs to initialize relative to gc->irq_base

`clr`

  IRQ_* bits to clear

`set`

  IRQ_* bits to set

#### Description

Remove up to 32 interrupts starting from gc->irq_base.

## Structures

This chapter contains the autogenerated documentation of the structures which are used in the generic IRQ layer.

### LINUX

Kernel Hackers Manual March 2018
struct irq_data
9
3.13.0-144-

### struct irq_data

per irq and irq chip data passed down to chip functions

#### Synopsis

    struct irq_data {
      u32 mask;
      unsigned int irq;
      unsigned long hwirq;
      unsigned int node;
      unsigned int state_use_accessors;
      struct irq_chip * chip;
      struct irq_domain * domain;
      void * handler_data;
      void * chip_data;
      struct msi_desc * msi_desc;
      cpumask_var_t affinity;
    };

#### Members

mask

  precomputed bitmask for accessing the chip registers

irq

  interrupt number

hwirq

  hardware interrupt number, local to the interrupt domain

node

  node index useful for balancing

state_use_accessors

  status information for irq chip functions. Use accessor functions to deal with it

chip

  low level interrupt hardware access

domain

  Interrupt translation domain; responsible for mapping between hwirq number and linux irq number.

handler_data

  per-IRQ data for the irq_chip methods

chip_data

  platform-specific per-chip private data for the chip methods, to allow shared chip implementations

msi_desc

  MSI descriptor

affinity

  IRQ affinity on SMP

#### Description

The fields here need to overlay the ones in irq_desc until we cleaned up the direct references and switched everything over to irq_data.

### LINUX

Kernel Hackers Manual March 2018
struct irq_chip
9
3.13.0-144-

### struct irq_chip

hardware interrupt chip descriptor

#### Synopsis

    struct irq_chip {
      const char * name;
      unsigned int	(* irq_startup) (struct irq_data *data);
      void (* irq_shutdown) (struct irq_data *data);
      void (* irq_enable) (struct irq_data *data);
      void (* irq_disable) (struct irq_data *data);
      void (* irq_ack) (struct irq_data *data);
      void (* irq_mask) (struct irq_data *data);
      void (* irq_mask_ack) (struct irq_data *data);
      void (* irq_unmask) (struct irq_data *data);
      void (* irq_eoi) (struct irq_data *data);
      int (* irq_set_affinity) (struct irq_data *data, const struct cpumask *dest, bool force);
      int (* irq_retrigger) (struct irq_data *data);
      int (* irq_set_type) (struct irq_data *data, unsigned int flow_type);
      int (* irq_set_wake) (struct irq_data *data, unsigned int on);
      void (* irq_bus_lock) (struct irq_data *data);
      void (* irq_bus_sync_unlock) (struct irq_data *data);
      void (* irq_cpu_online) (struct irq_data *data);
      void (* irq_cpu_offline) (struct irq_data *data);
      void (* irq_suspend) (struct irq_data *data);
      void (* irq_resume) (struct irq_data *data);
      void (* irq_pm_shutdown) (struct irq_data *data);
      void (* irq_calc_mask) (struct irq_data *data);
      void (* irq_print_chip) (struct irq_data *data, struct seq_file *p);
      unsigned long flags;
    };

#### Members

name

  name for /proc/interrupts

irq_startup

  start up the interrupt (defaults to ->enable if NULL)

irq_shutdown

  shut down the interrupt (defaults to ->disable if NULL)

irq_enable

  enable the interrupt (defaults to chip->unmask if NULL)

irq_disable

  disable the interrupt

irq_ack

  start of a new interrupt

irq_mask

  mask an interrupt source

irq_mask_ack

  ack and mask an interrupt source

irq_unmask

  unmask an interrupt source

irq_eoi

  end of interrupt

irq_set_affinity

  set the CPU affinity on SMP machines

irq_retrigger

  resend an IRQ to the CPU

irq_set_type

  set the flow type (IRQ_TYPE_LEVEL/etc.) of an IRQ

irq_set_wake

  enable/disable power-management wake-on of an IRQ

irq_bus_lock

  function to lock access to slow bus (i2c) chips

irq_bus_sync_unlock

  function to sync and unlock slow bus (i2c) chips

irq_cpu_online

  configure an interrupt source for a secondary CPU

irq_cpu_offline

  un-configure an interrupt source for a secondary CPU

irq_suspend

  function called from core code on suspend once per chip

irq_resume

  function called from core code on resume once per chip

irq_pm_shutdown

  function called from core code on shutdown once per chip

irq_calc_mask

  Optional function to set irq_data.mask for special cases

irq_print_chip

  optional to print special chip info in show_interrupts

flags

  chip specific flags

### LINUX

Kernel Hackers Manual March 2018
struct irq_chip_regs
9
3.13.0-144-

### struct irq_chip_regs

register offsets for struct irq_gci

#### Synopsis

    struct irq_chip_regs {
      unsigned long enable;
      unsigned long disable;
      unsigned long mask;
      unsigned long ack;
      unsigned long eoi;
      unsigned long type;
      unsigned long polarity;
    };

#### Members

enable

  Enable register offset to reg_base

disable

  Disable register offset to reg_base

mask

  Mask register offset to reg_base

ack

  Ack register offset to reg_base

eoi

  Eoi register offset to reg_base

type

  Type configuration register offset to reg_base

polarity

  Polarity configuration register offset to reg_base

### LINUX

Kernel Hackers Manual March 2018
struct irq_chip_type
9
3.13.0-144-

### struct irq_chip_type

Generic interrupt chip instance for a flow type

#### Synopsis

    struct irq_chip_type {
      struct irq_chip chip;
      struct irq_chip_regs regs;
      irq_flow_handler_t handler;
      u32 type;
      u32 mask_cache_priv;
      u32 * mask_cache;
    };

#### Members

chip

  The real interrupt chip which provides the callbacks

regs

  Register offsets for this chip

handler

  Flow handler associated with this chip

type

  Chip can handle these flow types

mask_cache_priv

  Cached mask register private to the chip type

mask_cache

  Pointer to cached mask register

#### Description

A irq_generic_chip can have several instances of irq_chip_type when it requires different functions and register offsets for different flow types.

### LINUX

Kernel Hackers Manual March 2018
struct irq_chip_generic
9
3.13.0-144-

### struct irq_chip_generic

Generic irq chip data structure

#### Synopsis

    struct irq_chip_generic {
      raw_spinlock_t lock;
      void __iomem * reg_base;
      unsigned int irq_base;
      unsigned int irq_cnt;
      u32 mask_cache;
      u32 type_cache;
      u32 polarity_cache;
      u32 wake_enabled;
      u32 wake_active;
      unsigned int num_ct;
      void * private;
      unsigned long installed;
      unsigned long unused;
      struct irq_domain * domain;
      struct list_head list;
      struct irq_chip_type chip_types[0];
    };

#### Members

lock

  Lock to protect register and cache data access

reg_base

  Register base address (virtual)

irq_base

  Interrupt base nr for this chip

irq_cnt

  Number of interrupts handled by this chip

mask_cache

  Cached mask register shared between all chip types

type_cache

  Cached type register

polarity_cache

  Cached polarity register

wake_enabled

  Interrupt can wakeup from suspend

wake_active

  Interrupt is marked as an wakeup from suspend source

num_ct

  Number of available irq_chip_type instances (usually 1)

private

  Private data for non generic chip callbacks

installed

  bitfield to denote installed interrupts

unused

  bitfield to denote unused interrupts

domain

  irq domain pointer

list

  List head for keeping track of instances

chip_types[0]

  Array of interrupt irq_chip_types

#### Description

Note, that irq_chip_generic can have multiple irq_chip_type implementations which can be associated to a particular irq line of an irq_chip_generic instance. That allows to share and protect state in an irq_chip_generic instance when we need to implement different flow mechanisms (level/edge) for it.

### LINUX

Kernel Hackers Manual March 2018
enum irq_gc_flags
9
3.13.0-144-

### enum irq_gc_flags

Initialization flags for generic irq chips

#### Synopsis

    enum irq_gc_flags {
      IRQ_GC_INIT_MASK_CACHE,
      IRQ_GC_INIT_NESTED_LOCK,
      IRQ_GC_MASK_CACHE_PER_TYPE,
      IRQ_GC_NO_MASK
    };

#### Constants

IRQ_GC_INIT_MASK_CACHE

  Initialize the mask_cache by reading mask reg

IRQ_GC_INIT_NESTED_LOCK

  Set the lock class of the irqs to nested for irq chips which need to call `irq_set_wake` on the parent irq. Usually GPIO implementations

IRQ_GC_MASK_CACHE_PER_TYPE

  Mask cache is chip type private

IRQ_GC_NO_MASK

  Do not calculate irq_data->mask

### LINUX

Kernel Hackers Manual March 2018
struct irqaction
9
3.13.0-144-

### struct irqaction

per interrupt action descriptor

#### Synopsis

    struct irqaction {
      irq_handler_t handler;
      void * dev_id;
      void __percpu * percpu_dev_id;
      struct irqaction * next;
      irq_handler_t thread_fn;
      struct task_struct * thread;
      unsigned int irq;
      unsigned int flags;
      unsigned long thread_flags;
      unsigned long thread_mask;
      const char * name;
      struct proc_dir_entry * dir;
    };

#### Members

handler

  interrupt handler function

dev_id

  cookie to identify the device

percpu_dev_id

  cookie to identify the device

next

  pointer to the next irqaction for shared interrupts

thread_fn

  interrupt handler function for threaded interrupts

thread

  thread pointer for threaded interrupts

irq

  interrupt number

flags

  flags (see IRQF_* above)

thread_flags

  flags related to `thread`

thread_mask

  bitmask for keeping track of `thread` activity

name

  name of the device

dir

  pointer to the proc/irq/NN/name entry

### LINUX

Kernel Hackers Manual March 2018
irq_set_affinity
9
3.13.0-144-

### irq_set_affinity

Set the irq affinity of a given irq

#### Synopsis

       int irq_set_affinity
       unsigned int irq
       const struct cpumask * cpumask

#### Arguments

`irq`

  Interrupt to set affinity

`cpumask`

  -- undescribed --

#### Description

Fails if cpumask does not contain an online CPU

### LINUX

Kernel Hackers Manual March 2018
irq_force_affinity
9
3.13.0-144-

### irq_force_affinity

Force the irq affinity of a given irq

#### Synopsis

       int irq_force_affinity
       unsigned int irq
       const struct cpumask * cpumask

#### Arguments

`irq`

  Interrupt to set affinity

`cpumask`

  -- undescribed --

#### Description

Same as irq_set_affinity, but without checking the mask against online cpus.

Solely for low level cpu hotplug code, where we need to make per cpu interrupts affine before the cpu becomes online.

### LINUX

Kernel Hackers Manual March 2018
struct irq_affinity_notify
9
3.13.0-144-

### struct irq_affinity_notify

context for notification of IRQ affinity changes

#### Synopsis

    struct irq_affinity_notify {
      unsigned int irq;
      struct kref kref;
      struct work_struct work;
      void (* notify) (struct irq_affinity_notify *, const cpumask_t *mask);
      void (* release) (struct kref *ref);
    };

#### Members

irq

  Interrupt to which notification applies

kref

  Reference count, for internal use

work

  Work item, for internal use

notify

  Function to be called on change. This will be called in process context.

release

  Function to be called on release. This will be called in process context. Once registered, the structure must only be freed when this function is called or later.

## Public Functions Provided

This chapter contains the autogenerated documentation of the kernel API functions which are exported.

### LINUX

Kernel Hackers Manual March 2018
synchronize_irq
9
3.13.0-144-

### synchronize_irq

wait for pending IRQ handlers (on other CPUs)

#### Synopsis

       void synchronize_irq
       unsigned int irq

#### Arguments

`irq`

  interrupt number to wait for

#### Description

This function waits for any pending IRQ handlers for this interrupt to complete before returning. If you use this function while holding a resource the IRQ handler may need you will deadlock.

This function may be called - with care - from IRQ context.

### LINUX

Kernel Hackers Manual March 2018
irq_set_affinity_notifier
9
3.13.0-144-

### irq_set_affinity_notifier

control notification of IRQ affinity changes

#### Synopsis

       int irq_set_affinity_notifier
       unsigned int irq
       struct irq_affinity_notify * notify

#### Arguments

`irq`

  Interrupt for which to enable/disable notification

`notify`

  Context for notification, or `NULL` to disable notification. Function pointers must be initialised; the other fields will be initialised by this function.

#### Description

Must be called in process context. Notification may only be enabled after the IRQ is allocated and must be disabled before the IRQ is freed using `free_irq`.

### LINUX

Kernel Hackers Manual March 2018
disable_irq_nosync
9
3.13.0-144-

### disable_irq_nosync

disable an irq without waiting

#### Synopsis

       void disable_irq_nosync
       unsigned int irq

#### Arguments

`irq`

  Interrupt to disable

#### Description

Disable the selected interrupt line. Disables and Enables are nested. Unlike `disable_irq`, this function does not ensure existing instances of the IRQ handler have completed before returning.

This function may be called from IRQ context.

### LINUX

Kernel Hackers Manual March 2018
disable_irq
9
3.13.0-144-

### disable_irq

disable an irq and wait for completion

#### Synopsis

       void disable_irq
       unsigned int irq

#### Arguments

`irq`

  Interrupt to disable

#### Description

Disable the selected interrupt line. Enables and Disables are nested. This function waits for any pending IRQ handlers for this interrupt to complete before returning. If you use this function while holding a resource the IRQ handler may need you will deadlock.

This function may be called - with care - from IRQ context.

### LINUX

Kernel Hackers Manual March 2018
enable_irq
9
3.13.0-144-

### enable_irq

enable handling of an irq

#### Synopsis

       void enable_irq
       unsigned int irq

#### Arguments

`irq`

  Interrupt to enable

#### Description

Undoes the effect of one call to `disable_irq`. If this matches the last disable, processing of interrupts on this IRQ line is re-enabled.

This function may be called from IRQ context only when desc->irq_data.chip->bus_lock and desc->chip->bus_sync_unlock are NULL !

### LINUX

Kernel Hackers Manual March 2018
irq_set_irq_wake
9
3.13.0-144-

### irq_set_irq_wake

control irq power management wakeup

#### Synopsis

       int irq_set_irq_wake
       unsigned int irq
       unsigned int on

#### Arguments

`irq`

  interrupt to control

`on`

  enable/disable power management wakeup

#### Description

Enable/disable power management wakeup mode, which is disabled by default. Enables and disables must match, just as they match for non-wakeup mode support.

Wakeup mode lets this IRQ wake the system from sleep states like suspend to RAM.

### LINUX

Kernel Hackers Manual March 2018
setup_irq
9
3.13.0-144-

### setup_irq

setup an interrupt

#### Synopsis

       int setup_irq
       unsigned int irq
       struct irqaction * act

#### Arguments

`irq`

  Interrupt line to setup

`act`

  irqaction for the interrupt

#### Description

Used to statically setup interrupts in the early boot process.

### LINUX

Kernel Hackers Manual March 2018
remove_irq
9
3.13.0-144-

### remove_irq

free an interrupt

#### Synopsis

       void remove_irq
       unsigned int irq
       struct irqaction * act

#### Arguments

`irq`

  Interrupt line to free

`act`

  irqaction for the interrupt

#### Description

Used to remove interrupts statically setup by the early boot process.

### LINUX

Kernel Hackers Manual March 2018
free_irq
9
3.13.0-144-

### free_irq

free an interrupt allocated with request_irq

#### Synopsis

       void free_irq
       unsigned int irq
       void * dev_id

#### Arguments

`irq`

  Interrupt line to free

`dev_id`

  Device identity to free

#### Description

Remove an interrupt handler. The handler is removed and if the interrupt line is no longer in use by any driver it is disabled. On a shared IRQ the caller must ensure the interrupt is disabled on the card it drives before calling this function. The function does not return until any executing interrupts for this IRQ have completed.

This function must not be called from interrupt context.

### LINUX

Kernel Hackers Manual March 2018
request_threaded_irq
9
3.13.0-144-

### request_threaded_irq

allocate an interrupt line

#### Synopsis

       int request_threaded_irq
       unsigned int irq
       irq_handler_t handler
       irq_handler_t thread_fn
       unsigned long irqflags
       const char * devname
       void * dev_id

#### Arguments

`irq`

  Interrupt line to allocate

`handler`

  Function to be called when the IRQ occurs. Primary handler for threaded interrupts If NULL and thread_fn != NULL the default primary handler is installed

`thread_fn`

  Function called from the irq handler thread If NULL, no irq thread is created

`irqflags`

  Interrupt type flags

`devname`

  An ascii name for the claiming device

`dev_id`

  A cookie passed back to the handler function

#### Description

This call allocates interrupt resources and enables the interrupt line and IRQ handling. From the point this call is made your handler function may be invoked. Since your handler function must clear any interrupt the board raises, you must take care both to initialise your hardware and to set up the interrupt handler in the right order.

If you want to set up a threaded irq handler for your device then you need to supply `handler` and `thread_fn`. `handler` is still called in hard interrupt context and has to check whether the interrupt originates from the device. If yes it needs to disable the interrupt on the device and return IRQ_WAKE_THREAD which will wake up the handler thread and run `thread_fn`. This split handler design is necessary to support shared interrupts.

Dev_id must be globally unique. Normally the address of the device data structure is used as the cookie. Since the handler receives this value it makes sense to use it.

If your interrupt is shared you must pass a non NULL dev_id as this is required when freeing the interrupt.

#### Flags

IRQF_SHARED Interrupt is shared IRQF_TRIGGER_* Specify active edge(s) or level

### LINUX

Kernel Hackers Manual March 2018
request_any_context_irq
9
3.13.0-144-

### request_any_context_irq

allocate an interrupt line

#### Synopsis

       int request_any_context_irq
       unsigned int irq
       irq_handler_t handler
       unsigned long flags
       const char * name
       void * dev_id

#### Arguments

`irq`

  Interrupt line to allocate

`handler`

  Function to be called when the IRQ occurs. Threaded handler for threaded interrupts.

`flags`

  Interrupt type flags

`name`

  An ascii name for the claiming device

`dev_id`

  A cookie passed back to the handler function

#### Description

This call allocates interrupt resources and enables the interrupt line and IRQ handling. It selects either a hardirq or threaded handling method depending on the context.

On failure, it returns a negative value. On success, it returns either IRQC_IS_HARDIRQ or IRQC_IS_NESTED.

### LINUX

Kernel Hackers Manual March 2018
irq_set_chip
9
3.13.0-144-

### irq_set_chip

set the irq chip for an irq

#### Synopsis

       int irq_set_chip
       unsigned int irq
       struct irq_chip * chip

#### Arguments

`irq`

  irq number

`chip`

  pointer to irq chip description structure

### LINUX

Kernel Hackers Manual March 2018
irq_set_irq_type
9
3.13.0-144-

### irq_set_irq_type

set the irq trigger type for an irq

#### Synopsis

       int irq_set_irq_type
       unsigned int irq
       unsigned int type

#### Arguments

`irq`

  irq number

`type`

  IRQ_TYPE_{LEVEL,EDGE}_* value - see include/linux/irq.h

### LINUX

Kernel Hackers Manual March 2018
irq_set_handler_data
9
3.13.0-144-

### irq_set_handler_data

set irq handler data for an irq

#### Synopsis

       int irq_set_handler_data
       unsigned int irq
       void * data

#### Arguments

`irq`

  Interrupt number

`data`

  Pointer to interrupt specific data

#### Description

Set the hardware irq controller data for an irq

### LINUX

Kernel Hackers Manual March 2018
irq_set_chip_data
9
3.13.0-144-

### irq_set_chip_data

set irq chip data for an irq

#### Synopsis

       int irq_set_chip_data
       unsigned int irq
       void * data

#### Arguments

`irq`

  Interrupt number

`data`

  Pointer to chip specific data

#### Description

Set the hardware irq chip data for an irq

### LINUX

Kernel Hackers Manual March 2018
handle_simple_irq
9
3.13.0-144-

### handle_simple_irq

Simple and software-decoded IRQs.

#### Synopsis

       void handle_simple_irq
       unsigned int irq
       struct irq_desc * desc

#### Arguments

`irq`

  the interrupt number

`desc`

  the interrupt description structure for this irq

#### Description

Simple interrupts are either sent from a demultiplexing interrupt handler or come from hardware, where no interrupt hardware control is necessary.

#### Note

The caller is expected to handle the ack, clear, mask and unmask issues if necessary.

### LINUX

Kernel Hackers Manual March 2018
handle_level_irq
9
3.13.0-144-

### handle_level_irq

Level type irq handler

#### Synopsis

       void handle_level_irq
       unsigned int irq
       struct irq_desc * desc

#### Arguments

`irq`

  the interrupt number

`desc`

  the interrupt description structure for this irq

#### Description

Level type interrupts are active as long as the hardware line has the active level. This may require to mask the interrupt and unmask it after the associated handler has acknowledged the device, so the interrupt line is back to inactive.

### LINUX

Kernel Hackers Manual March 2018
handle_edge_irq
9
3.13.0-144-

### handle_edge_irq

edge type IRQ handler

#### Synopsis

       void handle_edge_irq
       unsigned int irq
       struct irq_desc * desc

#### Arguments

`irq`

  the interrupt number

`desc`

  the interrupt description structure for this irq

#### Description

Interrupt occures on the falling and/or rising edge of a hardware signal. The occurrence is latched into the irq controller hardware and must be acked in order to be reenabled. After the ack another interrupt can happen on the same source even before the first one is handled by the associated event handler. If this happens it might be necessary to disable (mask) the interrupt depending on the controller hardware. This requires to reenable the interrupt inside of the loop which handles the interrupts which have arrived while the handler was running. If all pending interrupts are handled, the loop is left.

## Internal Functions Provided

This chapter contains the autogenerated documentation of the internal functions.

### LINUX

Kernel Hackers Manual March 2018
irq_reserve_irqs
9
3.13.0-144-

### irq_reserve_irqs

mark irqs allocated

#### Synopsis

       int irq_reserve_irqs
       unsigned int from
       unsigned int cnt

#### Arguments

`from`

  mark from irq number

`cnt`

  number of irqs to mark

#### Description

Returns 0 on success or an appropriate error code

### LINUX

Kernel Hackers Manual March 2018
irq_get_next_irq
9
3.13.0-144-

### irq_get_next_irq

get next allocated irq number

#### Synopsis

       unsigned int irq_get_next_irq
       unsigned int offset

#### Arguments

`offset`

  where to start the search

#### Description

Returns next irq number after offset or nr_irqs if none is found.

### LINUX

Kernel Hackers Manual March 2018
dynamic_irq_cleanup
9
3.13.0-144-

### dynamic_irq_cleanup

cleanup a dynamically allocated irq

#### Synopsis

       void dynamic_irq_cleanup
       unsigned int irq

#### Arguments

`irq`

  irq number to initialize

### LINUX

Kernel Hackers Manual March 2018
kstat_irqs_cpu
9
3.13.0-144-

### kstat_irqs_cpu

Get the statistics for an interrupt on a cpu

#### Synopsis

       unsigned int kstat_irqs_cpu
       unsigned int irq
       int cpu

#### Arguments

`irq`

  The interrupt number

`cpu`

  The cpu number

#### Description

Returns the sum of interrupt counts on `cpu` since boot for `irq`. The caller must ensure that the interrupt is not removed concurrently.

### LINUX

Kernel Hackers Manual March 2018
kstat_irqs
9
3.13.0-144-

### kstat_irqs

Get the statistics for an interrupt

#### Synopsis

       unsigned int kstat_irqs
       unsigned int irq

#### Arguments

`irq`

  The interrupt number

#### Description

Returns the sum of interrupt counts on all cpus since boot for `irq`. The caller must ensure that the interrupt is not removed concurrently.

### LINUX

Kernel Hackers Manual March 2018
kstat_irqs_usr
9
3.13.0-144-

### kstat_irqs_usr

Get the statistics for an interrupt

#### Synopsis

       unsigned int kstat_irqs_usr
       unsigned int irq

#### Arguments

`irq`

  The interrupt number

#### Description

Returns the sum of interrupt counts on all cpus since boot for `irq`. Contrary to `kstat_irqs` this can be called from any preemptible context. It's protected against concurrent removal of an interrupt descriptor when sparse irqs are enabled.

### LINUX

Kernel Hackers Manual March 2018
handle_bad_irq
9
3.13.0-144-

### handle_bad_irq

handle spurious and unhandled irqs

#### Synopsis

       void handle_bad_irq
       unsigned int irq
       struct irq_desc * desc

#### Arguments

`irq`

  the interrupt number

`desc`

  description of the interrupt

#### Description

Handles spurious and unhandled IRQ's. It also prints a debugmessage.

### LINUX

Kernel Hackers Manual March 2018
irq_set_msi_desc_off
9
3.13.0-144-

### irq_set_msi_desc_off

set MSI descriptor data for an irq at offset

#### Synopsis

       int irq_set_msi_desc_off
       unsigned int irq_base
       unsigned int irq_offset
       struct msi_desc * entry

#### Arguments

`irq_base`

  Interrupt number base

`irq_offset`

  Interrupt number offset

`entry`

  Pointer to MSI descriptor data

#### Description

Set the MSI descriptor entry for an irq at offset

### LINUX

Kernel Hackers Manual March 2018
irq_set_msi_desc
9
3.13.0-144-

### irq_set_msi_desc

set MSI descriptor data for an irq

#### Synopsis

       int irq_set_msi_desc
       unsigned int irq
       struct msi_desc * entry

#### Arguments

`irq`

  Interrupt number

`entry`

  Pointer to MSI descriptor data

#### Description

Set the MSI descriptor entry for an irq

### LINUX

Kernel Hackers Manual March 2018
irq_disable
9
3.13.0-144-

### irq_disable

Mark interrupt disabled

#### Synopsis

       void irq_disable
       struct irq_desc * desc

#### Arguments

`desc`

  irq descriptor which should be disabled

#### Description

If the chip does not implement the irq_disable callback, we use a lazy disable approach. That means we mark the interrupt disabled, but leave the hardware unmasked. That's an optimization because we avoid the hardware access for the common case where no interrupt happens after we marked it disabled. If an interrupt happens, then the interrupt flow handler masks the line at the hardware level and marks it pending.

### LINUX

Kernel Hackers Manual March 2018
handle_fasteoi_irq
9
3.13.0-144-

### handle_fasteoi_irq

irq handler for transparent controllers

#### Synopsis

       void handle_fasteoi_irq
       unsigned int irq
       struct irq_desc * desc

#### Arguments

`irq`

  the interrupt number

`desc`

  the interrupt description structure for this irq

#### Only a single callback will be issued to the chip

an ->`eoi` call when the interrupt has been serviced. This enables support for modern forms of interrupt handlers, which handle the flow details in hardware, transparently.

### LINUX

Kernel Hackers Manual March 2018
handle_edge_eoi_irq
9
3.13.0-144-

### handle_edge_eoi_irq

edge eoi type IRQ handler

#### Synopsis

       void handle_edge_eoi_irq
       unsigned int irq
       struct irq_desc * desc

#### Arguments

`irq`

  the interrupt number

`desc`

  the interrupt description structure for this irq

#### Description

Similar as the above handle_edge_irq, but using eoi and w/o the mask/unmask logic.

### LINUX

Kernel Hackers Manual March 2018
handle_percpu_irq
9
3.13.0-144-

### handle_percpu_irq

Per CPU local irq handler

#### Synopsis

       void handle_percpu_irq
       unsigned int irq
       struct irq_desc * desc

#### Arguments

`irq`

  the interrupt number

`desc`

  the interrupt description structure for this irq

#### Description

Per CPU interrupts on SMP machines without locking requirements

### LINUX

Kernel Hackers Manual March 2018
handle_percpu_devid_irq
9
3.13.0-144-

### handle_percpu_devid_irq

Per CPU local irq handler with per cpu dev ids

#### Synopsis

       void handle_percpu_devid_irq
       unsigned int irq
       struct irq_desc * desc

#### Arguments

`irq`

  the interrupt number

`desc`

  the interrupt description structure for this irq

#### Description

Per CPU interrupts on SMP machines without locking requirements. Same as `handle_percpu_irq` above but with the following extras:

action->percpu_dev_id is a pointer to percpu variables which contain the real device id for the cpu on which this handler is called

### LINUX

Kernel Hackers Manual March 2018
irq_cpu_online
9
3.13.0-144-

### irq_cpu_online

Invoke all irq_cpu_online functions.

#### Synopsis

       void irq_cpu_online
        void

#### Arguments

`void`

  no arguments

#### Description

Iterate through all irqs and invoke the chip.`irq_cpu_online` for each.

### LINUX

Kernel Hackers Manual March 2018
irq_cpu_offline
9
3.13.0-144-

### irq_cpu_offline

Invoke all irq_cpu_offline functions.

#### Synopsis

       void irq_cpu_offline
        void

#### Arguments

`void`

  no arguments

#### Description

Iterate through all irqs and invoke the chip.`irq_cpu_offline` for each.

## Credits

The following people have contributed to this document:

1. Thomas Gleixnertglx@linutronix.de

2. Ingo Molnarmingo@elte.hu