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charset="utf-8" Content-Transfer-Encoding: quoted-printable The following commit has been merged into the irq/cleanups branch of tip: Commit-ID: 809997b2b2d14b762e24829a0ce63a4a75e6185b Gitweb: https://git.kernel.org/tip/809997b2b2d14b762e24829a0ce63a4a7= 5e6185b Author: Jiri Slaby (SUSE) AuthorDate: Wed, 19 Mar 2025 10:29:47 +01:00 Committer: Thomas Gleixner CommitterDate: Wed, 07 May 2025 15:39:42 +02:00 Documentation: irq/concepts: Minor improvements Just note in the docs: 1) A PCI device as an example for shared interrupts 2) A sparse tree can be used for interrupts too 3) i8259s which have 8 pins [ tglx: Fix up subject prefix ] Signed-off-by: Jiri Slaby (SUSE) Signed-off-by: Thomas Gleixner Link: https://lore.kernel.org/all/20250319092951.37667-55-jirislaby@kernel.= org --- 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-a= pi/irq/concepts.rst index f166006..7c4564f 100644 --- a/Documentation/core-api/irq/concepts.rst +++ b/Documentation/core-api/irq/concepts.rst @@ -4,18 +4,20 @@ What is an IRQ? =20 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. =20 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. =20 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. =20 Architectures can assign additional meaning to the IRQ numbers, and are encouraged to in the case where there is any manual configuration