docs: add IRQ documentation at the core-api book

There are 4 IRQ documentation files under Documentation/*.txt.

Move them into a new directory (core-api/irq) and add a new
index file for it.

While here, use a title markup for the Debugging section of the
irq-domain.rst file.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/2da7485c3718e1442e6b4c2dd66857b776e8899b.1588345503.git.mchehab+huawei@kernel.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

1 files changed, 0 insertions, 24 deletions

diff --git a/Documentation/IRQ.txt b/Documentation/IRQ.txt
deleted file mode 100644
index 4273806a606b..000000000000
--- a/Documentation/IRQ.txt
+++ /dev/null
@@ -1,24 +0,0 @@
-===============
-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.