diff options
author | Eric W. Biederman <ebiederman@xmission.com> | 2006-06-29 05:25:02 -0400 |
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committer | Linus Torvalds <torvalds@g5.osdl.org> | 2006-06-29 13:26:25 -0400 |
commit | f702d7013c7470284843a6370aaa53b8b75c5a40 (patch) | |
tree | 1989bc89230b8319b3e2007b6e6238cc2dcec415 | |
parent | 98bb244b685eb2a297aa60fa2e5c0631f95828e1 (diff) |
[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>
-rw-r--r-- | Documentation/IRQ.txt | 22 |
1 files changed, 22 insertions, 0 deletions
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 @@ | |||
1 | What is an IRQ? | ||
2 | |||
3 | An IRQ is an interrupt request from a device. | ||
4 | Currently they can come in over a pin, or over a packet. | ||
5 | Several devices may be connected to the same pin thus | ||
6 | sharing an IRQ. | ||
7 | |||
8 | An IRQ number is a kernel identifier used to talk about a hardware | ||
9 | interrupt source. Typically this is an index into the global irq_desc | ||
10 | array, but except for what linux/interrupt.h implements the details | ||
11 | are architecture specific. | ||
12 | |||
13 | An IRQ number is an enumeration of the possible interrupt sources on a | ||
14 | machine. Typically what is enumerated is the number of input pins on | ||
15 | all of the interrupt controller in the system. In the case of ISA | ||
16 | what is enumerated are the 16 input pins on the two i8259 interrupt | ||
17 | controllers. | ||
18 | |||
19 | Architectures can assign additional meaning to the IRQ numbers, and | ||
20 | are encouraged to in the case where there is any manual configuration | ||
21 | of the hardware involved. The ISA IRQs are a classic example of | ||
22 | assigning this kind of additional meaning. | ||