From 225942f06e93dc4c24ce50df92e0eb5bcd2afbac Mon Sep 17 00:00:00 2001 From: "Jiri Slaby (SUSE)" Date: Wed, 19 Mar 2025 10:29:47 +0100 Subject: 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-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 -- cgit v1.2.3