The patch titled
genirq: irq: document what an IRQ is
has been added to the -mm tree. Its filename is
genirq-irq-document-what-an-irq-is.patch
See http://www.zip.com.au/~akpm/linux/patches/stuff/added-to-mm.txt to find
out what to do about this
------------------------------------------------------
Subject: genirq: irq: document what an IRQ is
From: Eric W. Biederman <ebiederman@xxxxxxxx>
Signed-off-by: Eric W. Biederman <ebiederm@xxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
Cc: Rajesh Shah <rajesh.shah@xxxxxxxxx>
Cc: Andi Kleen <ak@xxxxxx>
Cc: "Protasevich, Natalie" <Natalie.Protasevich@xxxxxxxxxx>
Cc: "Luck, Tony" <tony.luck@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxx>
---
Documentation/IRQ.txt | 22 ++++++++++++++++++++++
1 file changed, 22 insertions(+)
diff -puN /dev/null Documentation/IRQ.txt
--- /dev/null
+++ a/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.
_
Patches currently in -mm which might be from ebiederman@xxxxxxxx are
genirq-irq-document-what-an-irq-is.patch
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