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Diffstat (limited to 'Documentation/IRQ-domain.txt')
| -rw-r--r-- | Documentation/IRQ-domain.txt | 69 |
1 files changed, 49 insertions, 20 deletions
diff --git a/Documentation/IRQ-domain.txt b/Documentation/IRQ-domain.txt index 1f246eb25ca5..4a1cd7645d85 100644 --- a/Documentation/IRQ-domain.txt +++ b/Documentation/IRQ-domain.txt @@ -1,4 +1,6 @@ -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. |