lkml.org 
[lkml]   [2018]   [Oct]   [15]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH] of: overlay: update documentation to match current implementation
Date
From: Frank Rowand <frank.rowand@sony.com>

The overlay information in Documentation/devicetree/ is out of date.

Signed-off-by: Frank Rowand <frank.rowand@sony.com>
---
.../devicetree/dynamic-resolution-notes.txt | 24 ------
Documentation/devicetree/overlay-notes.txt | 93 ++++++++++------------
2 files changed, 42 insertions(+), 75 deletions(-)
delete mode 100644 Documentation/devicetree/dynamic-resolution-notes.txt

diff --git a/Documentation/devicetree/dynamic-resolution-notes.txt b/Documentation/devicetree/dynamic-resolution-notes.txt
deleted file mode 100644
index c24ec366c5dc..000000000000
--- a/Documentation/devicetree/dynamic-resolution-notes.txt
+++ /dev/null
@@ -1,24 +0,0 @@
-Device Tree Dynamic Resolver Notes
-----------------------------------
-
-This document describes the implementation of the in-kernel
-Device Tree resolver, residing in drivers/of/resolver.c
-
-How the resolver works
-----------------------
-
-The resolver is given as an input an arbitrary tree compiled with the
-proper dtc option and having a /plugin/ tag. This generates the
-appropriate __fixups__ & __local_fixups__ nodes.
-
-In sequence the resolver works by the following steps:
-
-1. Get the maximum device tree phandle value from the live tree + 1.
-2. Adjust all the local phandles of the tree to resolve by that amount.
-3. Using the __local__fixups__ node information adjust all local references
- by the same amount.
-4. For each property in the __fixups__ node locate the node it references
- in the live tree. This is the label used to tag the node.
-5. Retrieve the phandle of the target of the fixup.
-6. For each fixup in the property locate the node:property:offset location
- and replace it with the phandle value.
diff --git a/Documentation/devicetree/overlay-notes.txt b/Documentation/devicetree/overlay-notes.txt
index 725fb8d255c1..5b34b2318c59 100644
--- a/Documentation/devicetree/overlay-notes.txt
+++ b/Documentation/devicetree/overlay-notes.txt
@@ -2,8 +2,8 @@ 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.txt[1]
+device tree overlay functionality residing in drivers/of/overlay.c and
+drivers/of/resolver.c.

How overlays work
-----------------
@@ -34,26 +34,23 @@ Lets take an example where we have a foo board with the following base tree:
};
---- foo.dts -----------------------------------------------------------------

-The overlay bar.dts, when loaded (and resolved as described in [1]) should
+The overlay bar.dts, when processed by the devicetree resolver (as described
+later in this document) and applied to the live devicetree) will result in a
+live devicetree that is equivalent to foo+bar.dts.

---- bar.dts -----------------------------------------------------------------
/plugin/; /* allow undefined label references and record them */
/ {
- .... /* various properties for loader use; i.e. part id etc. */
- fragment@0 {
- target = <&ocp>;
- __overlay__ {
- /* bar peripheral */
- bar {
- compatible = "corp,bar";
- ... /* various properties and child nodes */
- }
- };
+ &ocp: {
+ /* bar peripheral */
+ bar {
+ compatible = "corp,bar";
+ ... /* various properties and child nodes */
+ }
};
};
---- bar.dts -----------------------------------------------------------------

-result in foo+bar.dts

---- foo+bar.dts -------------------------------------------------------------
/* FOO platform + bar peripheral */
@@ -78,14 +75,16 @@ result in 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
-is loaded the device will be created as expected.
+As a result of the overlay, a new device node (bar) has been created. Thus
+a bar platform device will have been registered. If a matching device
+driver is loaded the device will have been created as expected.

-Overlay in-kernel API
---------------------------------
+An overlay may specify the location of a node in the overlay with path
+notation as the label reference. In the bar.dts example above, '&ocp:'
+can also be expressed as '&{/ocp/}'.

-The API is quite easy to use.
+Overlay in-kernel API
+---------------------

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.
@@ -106,34 +105,26 @@ 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.

-Overlay DTS Format
-------------------
-
-The DTS of an overlay should have the following format:
-
-{
- /* ignored properties by the overlay */
-
- fragment@0 { /* first child node */
-
- target=<phandle>; /* phandle target of the overlay */
- or
- target-path="/path"; /* target path of the overlay */
-
- __overlay__ {
- property-a; /* add property-a to the target */
- node-a { /* add to an existing, or create a node-a */
- ...
- };
- };
- }
- fragment@1 { /* second child node */
- ...
- };
- /* more fragments follow */
-}
-
-Using the non-phandle based target method allows one to use a base DT which does
-not contain a __symbols__ node, i.e. it was not compiled with the -@ option.
-The __symbols__ node is only required for the target=<phandle> method, since it
-contains the information required to map from a phandle to a tree location.
+How the devicetree resolver works
+---------------------------------
+
+The resolver is given as an input an arbitrary devicetree source that contains
+a /plugin/ tag and has been compiled into an FDT. The FDT is unflattened into
+a detached devicetree. The resolver is responsible for updating the node
+phandle values the detached tree is updating the phandle values contained
+in properties in the detached tree.
+
+In sequence the resolver works by the following steps:
+
+1. Get the maximum devicetree phandle value from the live tree + 1. This
+ will be used as the phandle offset.
+2. Adjust all the node phandles of the detached tree by adding the phandle
+ offset.
+3. The local fixups metadata in the detached tree contains a list of property
+ values in the detached tree that are references to symbols in the detached
+ tree. Adjust these property values by adding the phandle offset.
+4. The fixups metadata in the detached tree contains a list of property
+ values in the detached tree that are references to symbols in the live
+ devicetree. For each of these property values, determine the phandle
+ value corresponding the the symbol and update the property value
+ accordingly.
--
Frank Rowand <frank.rowand@sony.com>
\
 
 \ /
  Last update: 2018-10-15 05:14    [W:0.040 / U:0.824 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site