docs: dt: convert overlay-notes.txt to ReST format

- Add a SPDX header;
- Adjust document title;
- Some whitespace fixes and new line breaks;
- Mark literal blocks as such;
- Add it to devicetree/index.rst.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: Rob Herring <robh@kernel.org>

1 files changed, 0 insertions, 124 deletions

diff --git a/Documentation/devicetree/overlay-notes.txt b/Documentation/devicetree/overlay-notes.txt
deleted file mode 100644
index b06ffcb8f0f8..000000000000
--- a/Documentation/devicetree/overlay-notes.txt
+++ /dev/null
@@ -1,124 +0,0 @@
-Device Tree Overlay Notes
--------------------------
-
-This document describes the implementation of the in-kernel
-device tree overlay functionality residing in drivers/of/overlay.c and is a
-companion document to Documentation/devicetree/dynamic-resolution-notes.rst[1]
-
-How overlays work
------------------
-
-A Device Tree's overlay purpose is to modify the kernel's live tree, and
-have the modification affecting the state of the kernel in a way that
-is reflecting the changes.
-Since the kernel mainly deals with devices, any new device node that result
-in an active device should have it created while if the device node is either
-disabled or removed all together, the affected device should be deregistered.
-
-Lets take an example where we have a foo board with the following base tree:
-
----- foo.dts -----------------------------------------------------------------
-	/* FOO platform */
-	/dts-v1/;
-	/ {
-		compatible = "corp,foo";
-
-		/* shared resources */
-		res: res {
-		};
-
-		/* On chip peripherals */
-		ocp: ocp {
-			/* peripherals that are always instantiated */
-			peripheral1 { ... };
-		};
-	};
----- foo.dts -----------------------------------------------------------------
-
-The overlay bar.dts,
-
----- bar.dts - overlay target location by label ------------------------------
-	/dts-v1/;
-	/plugin/;
-	&ocp {
-		/* bar peripheral */
-		bar {
-			compatible = "corp,bar";
-			... /* various properties and child nodes */
-		};
-	};
----- bar.dts -----------------------------------------------------------------
-
-when loaded (and resolved as described in [1]) should result in foo+bar.dts
-
----- foo+bar.dts -------------------------------------------------------------
-	/* FOO platform + bar peripheral */
-	/ {
-		compatible = "corp,foo";
-
-		/* shared resources */
-		res: res {
-		};
-
-		/* On chip peripherals */
-		ocp: ocp {
-			/* peripherals that are always instantiated */
-			peripheral1 { ... };
-
-			/* bar peripheral */
-			bar {
-				compatible = "corp,bar";
-				... /* various properties and child nodes */
-			};
-		};
-	};
----- foo+bar.dts -------------------------------------------------------------
-
-As a result of the overlay, a new device node (bar) has been created
-so a bar platform device will be registered and if a matching device driver
-is loaded the device will be created as expected.
-
-If the base DT was not compiled with the -@ option then the "&ocp" label
-will not be available to resolve the overlay node(s) to the proper location
-in the base DT. In this case, the target path can be provided. The target
-location by label syntax is preferred because the overlay can be applied to
-any base DT containing the label, no matter where the label occurs in the DT.
-
-The above bar.dts example modified to use target path syntax is:
-
----- bar.dts - overlay target location by explicit path ----------------------
-	/dts-v1/;
-	/plugin/;
-	&{/ocp} {
-		/* bar peripheral */
-		bar {
-			compatible = "corp,bar";
-			... /* various properties and child nodes */
-		}
-	};
----- bar.dts -----------------------------------------------------------------
-
-
-Overlay in-kernel API
---------------------------------
-
-The API is quite easy to use.
-
-1. Call of_overlay_fdt_apply() to create and apply an overlay changeset. The
-return value is an error or a cookie identifying this overlay.
-
-2. Call of_overlay_remove() to remove and cleanup the overlay changeset
-previously created via the call to of_overlay_fdt_apply(). Removal of an
-overlay changeset that is stacked by another will not be permitted.
-
-Finally, if you need to remove all overlays in one-go, just call
-of_overlay_remove_all() which will remove every single one in the correct
-order.
-
-In addition, there is the option to register notifiers that get called on
-overlay operations. See of_overlay_notifier_register/unregister and
-enum of_overlay_notify_action for details.
-
-Note that a notifier callback is not supposed to store pointers to a device
-tree node or its content beyond OF_OVERLAY_POST_REMOVE corresponding to the
-respective node it received.