From: Eric W. Biederman Date: Thu, 29 Jun 2006 09:25:02 +0000 (-0700) Subject: [PATCH] genirq: irq: document what an IRQ is X-Git-Tag: upstream/snapshot3+hdmi~39428 X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=f702d7013c7470284843a6370aaa53b8b75c5a40;p=platform%2Fadaptation%2Frenesas_rcar%2Frenesas_kernel.git [PATCH] genirq: irq: document what an IRQ is Signed-off-by: Eric W. Biederman Cc: Ingo Molnar Cc: Thomas Gleixner Cc: Benjamin Herrenschmidt Cc: Rajesh Shah Cc: Andi Kleen Cc: "Protasevich, Natalie" Cc: "Luck, Tony" Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- diff --git a/Documentation/IRQ.txt b/Documentation/IRQ.txt new file mode 100644 index 0000000..1011e71 --- /dev/null +++ b/Documentation/IRQ.txt @@ -0,0 +1,22 @@ +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.