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Diffstat (limited to 'Documentation/core-api/irq/concepts.rst')
| -rw-r--r-- | Documentation/core-api/irq/concepts.rst | 27 |
1 files changed, 14 insertions, 13 deletions
diff --git a/Documentation/core-api/irq/concepts.rst b/Documentation/core-api/irq/concepts.rst index 4273806a606b..7c4564f3cbdf 100644 --- a/Documentation/core-api/irq/concepts.rst +++ b/Documentation/core-api/irq/concepts.rst @@ -2,23 +2,24 @@ What is an IRQ? =============== -An IRQ is an interrupt request from a device. -Currently they can come in over a pin, or over a packet. -Several devices may be connected to the same pin thus -sharing an IRQ. +An IRQ is an interrupt request from a device. Currently, they can come +in over a pin, or over a packet. Several devices may be connected to +the same pin thus sharing an IRQ. Such as on legacy PCI bus: All devices +typically share 4 lanes/pins. Note that each device can request an +interrupt on each of the lanes. An IRQ number is a kernel identifier used to talk about a hardware -interrupt source. Typically this is an index into the global irq_desc -array, but except for what linux/interrupt.h implements the details -are architecture specific. +interrupt source. Typically, this is an index into the global irq_desc +array or sparse_irqs tree. But except for what linux/interrupt.h +implements, the details are architecture specific. An IRQ number is an enumeration of the possible interrupt sources on a -machine. Typically what is enumerated is the number of input pins on -all of the interrupt controller in the system. In the case of ISA -what is enumerated are the 16 input pins on the two i8259 interrupt -controllers. +machine. Typically, what is enumerated is the number of input pins on +all of the interrupt controllers in the system. In the case of ISA, +what is enumerated are the 8 input pins on each of the two i8259 +interrupt controllers. Architectures can assign additional meaning to the IRQ numbers, and -are encouraged to in the case where there is any manual configuration -of the hardware involved. The ISA IRQs are a classic example of +are encouraged to in the case where there is any manual configuration +of the hardware involved. The ISA IRQs are a classic example of assigning this kind of additional meaning. |