From e750b9772fe822bb5b23d1f5c158bdc48ad2b828 Mon Sep 17 00:00:00 2001
From: "Eric W. Biederman" <ebiederman@xmission.com>
Date: Thu, 29 Jun 2006 02:25:02 -0700
Subject: [PATCH] --- yaml --- r: 31084 b: refs/heads/master c:
 f702d7013c7470284843a6370aaa53b8b75c5a40 h: refs/heads/master v: v3

---
 [refs]                      |  2 +-
 trunk/Documentation/IRQ.txt | 22 ++++++++++++++++++++++
 2 files changed, 23 insertions(+), 1 deletion(-)
 create mode 100644 trunk/Documentation/IRQ.txt

diff --git a/[refs] b/[refs]
index 36df7df45c48..e0afca8f6457 100644
--- a/[refs]
+++ b/[refs]
@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 98bb244b685eb2a297aa60fa2e5c0631f95828e1
+refs/heads/master: f702d7013c7470284843a6370aaa53b8b75c5a40
diff --git a/trunk/Documentation/IRQ.txt b/trunk/Documentation/IRQ.txt
new file mode 100644
index 000000000000..1011e7175021
--- /dev/null
+++ b/trunk/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.