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Date: Mon, 4 May 2020 15:16:40 -0500
From: Frank Rowand <frowand.list@...il.com>
To: Rob Herring <robh+dt@...nel.org>, pantelis.antoniou@...sulko.com
Cc: devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
Geert Uytterhoeven <geert+renesas@...der.be>,
Alan Tull <atull@...nel.org>,
Mauro Carvalho Chehab <mchehab+huawei@...nel.org>
Subject: Re: [PATCH v2] of: Documentation: change overlay example to use
current syntax
Hi Rob,
Ping.
There is a conflict between this and Mauro's v3 patch at:
https://lore.kernel.org/r/cover.1586961793.git.mchehab+huawei@kernel.org
I pointed out the conflict to Mauro in his v2 patch, and he said he would
rebase on a new -next to resolve the conflict. Unfortunately my patch
was not in -next, so the conflict remains.
If Mauro's patches should go in first, I can redo my patches on top of
his, after his go in.
-Frank
On 1/27/20 6:37 PM, frowand.list@...il.com wrote:
> From: Frank Rowand <frank.rowand@...y.com>
>
> The overlay implementation details in the compiled (DTB) file are
> now properly implemented by the dtc compiler and should no longer
> be hard coded in the source file.
>
> Signed-off-by: Frank Rowand <frank.rowand@...y.com>
> ---
>
> changes since v1:
> - fixed typo in patch comment (implementation)
>
> Documentation/devicetree/overlay-notes.txt | 85 ++++++++++++------------------
> 1 file changed, 35 insertions(+), 50 deletions(-)
>
> diff --git a/Documentation/devicetree/overlay-notes.txt b/Documentation/devicetree/overlay-notes.txt
> index 725fb8d255c1..fddc63da7dba 100644
> --- a/Documentation/devicetree/overlay-notes.txt
> +++ b/Documentation/devicetree/overlay-notes.txt
> @@ -19,6 +19,7 @@ Lets take an example where we have a foo board with the following base tree:
>
> ---- foo.dts -----------------------------------------------------------------
> /* FOO platform */
> + /dts-v1/;
> / {
> compatible = "corp,foo";
>
> @@ -30,30 +31,25 @@ Lets take an example where we have a foo board with the following base tree:
> ocp: ocp {
> /* peripherals that are always instantiated */
> peripheral1 { ... };
> - }
> + };
> };
> ---- foo.dts -----------------------------------------------------------------
>
> -The overlay bar.dts, when loaded (and resolved as described in [1]) should
> +The overlay 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 */
> - }
> +---- bar.dts - overlay target location by label ------------------------------
> + /dts-v1/;
> + /plugin/;
> + &ocp {
> + /* bar peripheral */
> + bar {
> + compatible = "corp,bar";
> + ... /* various properties and child nodes */
> };
> };
> -};
> ---- bar.dts -----------------------------------------------------------------
>
> -result in foo+bar.dts
> +when loaded (and resolved as described in [1]) should result in foo+bar.dts
>
> ---- foo+bar.dts -------------------------------------------------------------
> /* FOO platform + bar peripheral */
> @@ -73,8 +69,8 @@ result in foo+bar.dts
> bar {
> compatible = "corp,bar";
> ... /* various properties and child nodes */
> - }
> - }
> + };
> + };
> };
> ---- foo+bar.dts -------------------------------------------------------------
>
> @@ -82,6 +78,27 @@ 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
> --------------------------------
>
> @@ -105,35 +122,3 @@ 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.
> -
> -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.
>
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