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diff --git a/Documentation/core-api/irq/irq-domain.rst b/Documentation/core-api/irq/irq-domain.rst index f88a6ee67a35..68eb2612e8a4 100644 --- a/Documentation/core-api/irq/irq-domain.rst +++ b/Documentation/core-api/irq/irq-domain.rst @@ -1,75 +1,91 @@ =============================================== -The 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. -This is simple when there is only one interrupt controller, but in -systems with multiple interrupt controllers the kernel must ensure +space where each separate IRQ source is assigned a unique number. +This is simple when there is only one interrupt controller. But in +systems with multiple interrupt controllers, the kernel must ensure that each one gets assigned non-overlapping allocations of Linux IRQ numbers. The number of interrupt controllers registered as unique irqchips -show a rising tendency: for example subdrivers of different kinds +shows a rising tendency. For example, subdrivers of different kinds such as GPIO controllers avoid reimplementing identical callback mechanisms as the IRQ core system by modelling their interrupt -handlers as irqchips, i.e. in effect cascading interrupt controllers. +handlers as irqchips. I.e. in effect cascading interrupt controllers. -Here the interrupt number loose all kind of correspondence to -hardware interrupt numbers: whereas in the past, IRQ numbers could -be chosen so they matched the hardware IRQ line into the root -interrupt controller (i.e. the component actually fireing the -interrupt line to the CPU) nowadays this number is just a number. +So in the past, IRQ numbers could be chosen so that they match the +hardware IRQ line into the root interrupt controller (i.e. the +component actually firing the interrupt line to the CPU). Nowadays, +this number is just a number and the number has no +relationship to hardware interrupt numbers. -For this reason we need a mechanism to separate controller-local -interrupt numbers, called hardware irq's, from Linux IRQ numbers. +For this reason, we need a mechanism to separate controller-local +interrupt numbers, called hardware IRQs, from Linux IRQ numbers. The irq_alloc_desc*() and irq_free_desc*() APIs provide allocation of -irq numbers, but they don't provide any support for reverse mapping of +IRQ numbers, but they don't provide any support for reverse mapping of the controller-local IRQ (hwirq) number into the Linux IRQ number space. -The irq_domain library adds mapping between hwirq and IRQ numbers on -top of the irq_alloc_desc*() API. An irq_domain to manage mapping is -preferred over interrupt controller drivers open coding their own +The irq_domain library adds a mapping between hwirq and IRQ numbers on +top of the irq_alloc_desc*() API. An irq_domain to manage the mapping +is preferred over interrupt controller drivers open coding their own reverse mapping scheme. -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 also implements a translation from an abstract struct +irq_fwspec to hwirq numbers (Device Tree, non-DT firmware node, ACPI +GSI, and software node so far), and can be easily extended to support +other IRQ topology data sources. The implementation is performed +without any extra platform support code. -irq_domain usage +irq_domain Usage ================ - -An interrupt controller driver creates and registers an irq_domain by -calling one of the irq_domain_add_*() or irq_domain_create_*() functions -(each mapping method has a different allocator function, more on that later). -The function will return a pointer to the irq_domain on success. The caller -must provide the allocator function with an irq_domain_ops structure. +struct irq_domain could be defined as an irq domain controller. That +is, it handles the mapping between hardware and virtual interrupt +numbers for a given interrupt domain. The domain structure is +generally created by the PIC code for a given PIC instance (though a +domain can cover more than one PIC if they have a flat number model). +It is the domain callbacks that are responsible for setting the +irq_chip on a given irq_desc after it has been mapped. + +The host code and data structures use a fwnode_handle pointer to +identify the domain. In some cases, and in order to preserve source +code compatibility, this fwnode pointer is "upgraded" to a DT +device_node. For those firmware infrastructures that do not provide a +unique identifier for an interrupt controller, the irq_domain code +offers a fwnode allocator. + +An interrupt controller driver creates and registers a struct irq_domain +by calling one of the irq_domain_create_*() functions (each mapping +method has a different allocator function, more on that later). The +function will return a pointer to the struct irq_domain on success. The +caller must provide the allocator function with a struct irq_domain_ops +pointer. In most cases, the irq_domain will begin empty without any mappings between hwirq and IRQ numbers. Mappings are added to the irq_domain by calling irq_create_mapping() which accepts the irq_domain and a -hwirq number as arguments. If a mapping for the hwirq doesn't already -exist then it will allocate a new Linux irq_desc, associate it with -the hwirq, and call the .map() callback so the driver can perform any -required hardware setup. +hwirq number as arguments. If a mapping for the hwirq doesn't already +exist, irq_create_mapping() allocates a new Linux irq_desc, associates +it with the hwirq, and calls the :c:member:`irq_domain_ops.map()` +callback. In there, the driver can perform any required hardware +setup. Once a mapping has been established, it can be retrieved or used via a variety of methods: - irq_resolve_mapping() returns a pointer to the irq_desc structure - for a given domain and hwirq number, and NULL if there was no + for a given domain and hwirq number, or NULL if there was no mapping. - irq_find_mapping() returns a Linux IRQ number for a given domain and - hwirq number, and 0 if there was no mapping -- irq_linear_revmap() is now identical to irq_find_mapping(), and is - deprecated + hwirq number, or 0 if there was no mapping - generic_handle_domain_irq() handles an interrupt described by a domain and a hwirq number -Note that irq domain lookups must happen in contexts that are -compatible with a RCU read-side critical section. +Note that irq_domain lookups must happen in contexts that are +compatible with an RCU read-side critical section. The irq_create_mapping() function must be called *at least once* before any call to irq_find_mapping(), lest the descriptor will not @@ -77,13 +93,14 @@ be allocated. 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. +callbacks) then it can be directly obtained from +:c:member:`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. +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: @@ -92,48 +109,36 @@ Linear :: - irq_domain_add_linear() irq_domain_create_linear() -The linear reverse map maintains a fixed size table indexed by the +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 the hwirq, and the IRQ number is stored in the table. The Linear map is a good choice when the maximum number of hwirqs is fixed and a relatively small number (~ < 256). The advantages of this -map are fixed time lookup for IRQ numbers, and irq_descs are only +map are fixed-time lookup for IRQ numbers, and irq_descs are only allocated for in-use IRQs. The disadvantage is that the table must be as large as the largest possible hwirq number. -irq_domain_add_linear() and irq_domain_create_linear() are functionally -equivalent, except for the first argument is different - the former -accepts an Open Firmware specific 'struct device_node', while the latter -accepts a more general abstraction 'struct fwnode_handle'. - -The majority of drivers should use the linear map. +The majority of drivers should use the Linear map. 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 hwirq is used as the lookup key for the radix tree. -The tree map is a good choice if the hwirq number can be very large +The Tree map is a good choice if the hwirq number can be very large since it doesn't need to allocate a table as large as the largest hwirq number. The disadvantage is that hwirq to IRQ number lookup is dependent on how many entries are in the table. -irq_domain_add_tree() and irq_domain_create_tree() are functionally -equivalent, except for the first argument is different - the former -accepts an Open Firmware specific 'struct device_node', while the latter -accepts a more general abstraction 'struct fwnode_handle'. - Very few drivers should need this mapping. No Map @@ -141,7 +146,7 @@ No Map :: - irq_domain_add_nomap() + irq_domain_create_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 @@ -159,17 +164,15 @@ Legacy :: - irq_domain_add_simple() - irq_domain_add_legacy() irq_domain_create_simple() irq_domain_create_legacy() 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 -driver cannot be immediately converted to use the linear mapping. For +driver cannot be immediately converted to use the Linear mapping. For example, many embedded system board support files use a set of #defines for IRQ numbers that are passed to struct device registrations. In that -case the Linux IRQ numbers cannot be dynamically assigned and the legacy +case the Linux IRQ numbers cannot be dynamically assigned and the Legacy mapping should be used. As the name implies, the \*_legacy() functions are deprecated and only @@ -177,25 +180,25 @@ exist to ease the support of ancient platforms. No new users should be added. Same goes for the \*_simple() functions when their use results in the legacy behaviour. -The legacy map assumes a contiguous range of IRQ numbers has already +The Legacy map assumes a contiguous range of IRQ numbers has already been allocated for the controller and that the IRQ number can be calculated by adding a fixed offset to the hwirq number, and visa-versa. The disadvantage is that it requires the interrupt controller to manage IRQ allocations and it requires an irq_desc to be allocated for every hwirq, even if it is unused. -The legacy map should only be used if fixed IRQ mappings must be -supported. For example, ISA controllers would use the legacy map for +The Legacy map should only be used if fixed IRQ mappings must be +supported. For example, ISA controllers would use the Legacy map for mapping Linux IRQs 0-15 so that existing ISA drivers get the correct IRQ numbers. -Most users of legacy mappings should use irq_domain_add_simple() or -irq_domain_create_simple() which will use a legacy domain only if an IRQ range -is supplied by the system and will otherwise use a linear domain mapping. -The semantics of this call are such that if an IRQ range is specified then -descriptors will be allocated on-the-fly for it, and if no range is -specified it will fall through to irq_domain_add_linear() or -irq_domain_create_linear() which means *no* irq descriptors will be allocated. +Most users of legacy mappings should use irq_domain_create_simple() +which will use a legacy domain only if an IRQ range is supplied by the +system and will otherwise use a linear domain mapping. The semantics of +this call are such that if an IRQ range is specified then descriptors +will be allocated on-the-fly for it, and if no range is specified it +will fall through to irq_domain_create_linear() which means *no* IRQ +descriptors will be allocated. A typical use case for simple domains is where an irqchip provider is supporting both dynamic and static IRQ assignments. @@ -206,18 +209,12 @@ 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. -irq_domain_add_simple() and irq_domain_create_simple() as well as -irq_domain_add_legacy() and irq_domain_create_legacy() are functionally -equivalent, except for the first argument is different - the former -accepts an Open Firmware specific 'struct device_node', while the latter -accepts a more general abstraction 'struct fwnode_handle'. - -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 delivery path on x86 platforms:: Device --> IOAPIC -> Interrupt remapping Controller -> Local APIC -> CPU @@ -230,8 +227,8 @@ There are three interrupt controllers involved: To support such a hardware topology and make software architecture match 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 +When building irq_domain hierarchy, the irq_domain nearest the device is +child and the irq_domain nearest the CPU is parent. So a hierarchy structure as below will be built for the example above:: CPU Vector irq_domain (root irq_domain to manage CPU vectors) @@ -253,20 +250,40 @@ 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: +The following is needed to support hierarchy irq_domain: -1) a new field 'parent' is added to struct irq_domain; it's used to +1) The :c:member:`parent` field in struct irq_domain is used to maintain irq_domain hierarchy information. -2) a new field 'parent_data' is added to struct irq_data; it's used to - build hierarchy irq_data to match hierarchy irq_domains. The irq_data - is used to store irq_domain pointer and hardware irq number. -3) new callbacks are added to struct irq_domain_ops to support hierarchy - irq_domain operations. - -With support of hierarchy irq_domain and hierarchy irq_data ready, an -irq_domain structure is built for each interrupt controller, and an +2) The :c:member:`parent_data` field in struct irq_data is used to + build hierarchy irq_data to match hierarchy irq_domains. The + irq_data is used to store irq_domain pointer and hardware irq + number. +3) The :c:member:`alloc()`, :c:member:`free()`, and other callbacks in + struct irq_domain_ops to support hierarchy irq_domain operations. + +With the support of hierarchy irq_domain and hierarchy irq_data ready, +an irq_domain structure is built for each interrupt controller, and an irq_data structure is allocated for each irq_domain associated with an -IRQ. Now we could go one step further to support stacked(hierarchy) +IRQ. + +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(). +3) Optionally, implement an irq_chip to manage the interrupt controller + hardware. +4) There is no need to implement irq_domain_ops.map() and + irq_domain_ops.unmap(). They are unused with hierarchy irq_domain. + +Note the hierarchy irq_domain is in no way x86-specific, and is +heavily used to support other architectures, such as ARM, ARM64 etc. + +Stacked irq_chip +~~~~~~~~~~~~~~~~ + +Now, we could go one step further to support stacked (hierarchy) irq_chip. That is, an irq_chip is associated with each irq_data along the hierarchy. A child irq_chip may implement a required action by itself or by cooperating with its parent irq_chip. @@ -276,22 +293,28 @@ with the hardware managed by itself and may ask for services from its parent irq_chip when needed. So we could achieve a much cleaner 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. -3) Optionally implement an irq_chip to manage the interrupt controller - hardware. -4) No need to implement irq_domain_ops.map and irq_domain_ops.unmap, - they are unused with hierarchy irq_domain. - -Hierarchy irq_domain is in no way x86 specific, and is heavily used to -support other architectures, such as ARM, ARM64 etc. - Debugging ========= Most of the internals of the IRQ subsystem are exposed in debugfs by turning CONFIG_GENERIC_IRQ_DEBUGFS on. + +Structures and Public Functions Provided +======================================== + +This chapter contains the autogenerated documentation of the structures +and exported kernel API functions which are used for IRQ domains. + +.. kernel-doc:: include/linux/irqdomain.h + +.. kernel-doc:: kernel/irq/irqdomain.c + :export: + +Internal Functions Provided +=========================== + +This chapter contains the autogenerated documentation of the internal +functions. + +.. kernel-doc:: kernel/irq/irqdomain.c + :internal: |