From 76cb841cb886eef6b3bee341a2266c76578724ad Mon Sep 17 00:00:00 2001 From: Daniel Baumann Date: Mon, 6 May 2024 03:02:30 +0200 Subject: Adding upstream version 4.19.249. Signed-off-by: Daniel Baumann --- Documentation/IRQ.txt | 24 ++++++++++++++++++++++++ 1 file changed, 24 insertions(+) create mode 100644 Documentation/IRQ.txt (limited to 'Documentation/IRQ.txt') diff --git a/Documentation/IRQ.txt b/Documentation/IRQ.txt new file mode 100644 index 000000000..4273806a6 --- /dev/null +++ b/Documentation/IRQ.txt @@ -0,0 +1,24 @@ +=============== +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 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. + +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. + +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 +assigning this kind of additional meaning. -- cgit v1.2.3