Just note in the docs: 1) A PCI as an example for shared interrupts, 2) a sparse tree can be used for interrupts too, and 3) two i8259s have 8 pins. Signed-off-by: Jiri Slaby (SUSE) <jirislaby@xxxxxxxxxx> Cc: Jonathan Corbet <corbet@xxxxxxx> Cc: linux-doc@xxxxxxxxxxxxxxx Cc: Randy Dunlap <rdunlap@xxxxxxxxxxxxx> --- Documentation/core-api/irq/concepts.rst | 12 +++++++----- 1 file changed, 7 insertions(+), 5 deletions(-) diff --git a/Documentation/core-api/irq/concepts.rst b/Documentation/core-api/irq/concepts.rst index f166006a81f6..7c4564f3cbdf 100644 --- a/Documentation/core-api/irq/concepts.rst +++ b/Documentation/core-api/irq/concepts.rst @@ -4,18 +4,20 @@ 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. +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. +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 controllers in the system. In the case of ISA, -what is enumerated are the 16 input pins on the two i8259 interrupt -controllers. +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 -- 2.48.0
