Commit 642e6e5c authored by Mauro Carvalho Chehab's avatar Mauro Carvalho Chehab Committed by Rob Herring
Browse files

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: default avatarMauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: default avatarRob Herring <robh@kernel.org>
parent 218e1b3d

Documentation/devicetree/index.rst

+1 −0
Original line number Diff line number Diff line
@@ -12,3 +12,4 @@ Open Firmware and Device Tree 
   changesets

   dynamic-resolution-notes

   of_unittest

   overlay-notes

Documentation/devicetree/overlay-notes.txt→Documentation/devicetree/overlay-notes.rst

+21 −17
Original line number Diff line number Diff line 
.. SPDX-License-Identifier: GPL-2.0



=========================

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
@@ -15,9 +18,9 @@ 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:

Lets take an example where we have a foo board with the following base tree::



---- foo.dts -----------------------------------------------------------------

    ---- foo.dts ---------------------------------------------------------------

	/* FOO platform */

	/dts-v1/;

	/ {
@@ -33,11 +36,12 @@ Lets take an example where we have a foo board with the following base tree: 
			peripheral1 { ... };

		};

	};

---- foo.dts -----------------------------------------------------------------

    ---- foo.dts ---------------------------------------------------------------



The overlay bar.dts,

::



---- bar.dts - overlay target location by label ------------------------------

    ---- bar.dts - overlay target location by label ----------------------------

	/dts-v1/;

	/plugin/;

	&ocp {
@@ -47,11 +51,11 @@ The overlay bar.dts, 
			... /* various properties and child nodes */

		};

	};

---- bar.dts -----------------------------------------------------------------

    ---- bar.dts ---------------------------------------------------------------



when loaded (and resolved as described in [1]) should result in foo+bar.dts

when loaded (and resolved as described in [1]) should result in foo+bar.dts::



---- foo+bar.dts -------------------------------------------------------------

    ---- foo+bar.dts -----------------------------------------------------------

	/* FOO platform + bar peripheral */

	/ {

		compatible = "corp,foo";
@@ -72,7 +76,7 @@ when loaded (and resolved as described in [1]) should result in foo+bar.dts 
			};

		};

	};

---- foo+bar.dts -------------------------------------------------------------

    ---- 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
@@ -84,9 +88,9 @@ 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:

The above bar.dts example modified to use target path syntax is::



---- bar.dts - overlay target location by explicit path ----------------------

    ---- bar.dts - overlay target location by explicit path --------------------

	/dts-v1/;

	/plugin/;

	&{/ocp} {
@@ -96,7 +100,7 @@ The above bar.dts example modified to use target path syntax is: 
			... /* various properties and child nodes */

		}

	};

---- bar.dts -----------------------------------------------------------------

    ---- bar.dts ---------------------------------------------------------------





Overlay in-kernel API
@@ -104,10 +108,10 @@ 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

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

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.

MAINTAINERS

+1 −1
Original line number Diff line number Diff line
@@ -12536,7 +12536,7 @@ M: Frank Rowand <frowand.list@gmail.com> 
L:	devicetree@vger.kernel.org

S:	Maintained

F:	Documentation/devicetree/dynamic-resolution-notes.rst

F:	Documentation/devicetree/overlay-notes.txt

F:	Documentation/devicetree/overlay-notes.rst

F:	drivers/of/overlay.c

F:	drivers/of/resolver.c

K:	of_overlay_notifier_

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