From: Eric W. Biederman <ebiederman@xmission.com> Date: Thu, 29 Jun 2006 09:25:02 +0000 (-0700) Subject: [PATCH] genirq: irq: document what an IRQ is X-Git-Url: https://git.stricted.de/?a=commitdiff_plain;h=f702d7013c7470284843a6370aaa53b8b75c5a40;p=GitHub%2Fexynos8895%2Fandroid_kernel_samsung_universal8895.git [PATCH] genirq: irq: document what an IRQ is Signed-off-by: Eric W. Biederman <ebiederm@xmission.com> Cc: Ingo Molnar <mingo@elte.hu> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Rajesh Shah <rajesh.shah@intel.com> Cc: Andi Kleen <ak@muc.de> Cc: "Protasevich, Natalie" <Natalie.Protasevich@UNISYS.com> Cc: "Luck, Tony" <tony.luck@intel.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org> --- diff --git a/Documentation/IRQ.txt b/Documentation/IRQ.txt new file mode 100644 index 000000000000..1011e7175021 --- /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.