linux-kernel - Re: [PATCH 3/6] doc: dt: Document the indirect overlay method.

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Date:	Tue, 10 May 2016 16:59:06 +0300
From:	Pantelis Antoniou <pantelis.antoniou@...sulko.com>
To:	Rob Herring <robherring2@...il.com>
Cc:	Frank Rowand <frowand.list@...il.com>,
	Matt Porter <mporter@...sulko.com>,
	Grant Likely <grant.likely@...retlab.ca>,
	Koen Kooi <koen@...inion.thruhere.net>,
	Guenter Roeck <linux@...ck-us.net>,
	Marek Vasut <marex@...x.de>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/6] doc: dt: Document the indirect overlay method.

Hi Rob,

> On May 10, 2016, at 00:59 , Rob Herring <robherring2@...il.com> wrote:
> 
> On Mon, May 9, 2016 at 1:05 PM, Pantelis Antoniou
> <pantelis.antoniou@...sulko.com> wrote:
>> Add a description of the indirect overlay method to the overlay
>> documention file.
> 
> Why? Please write some decent commit messages.
> 
>> Signed-off-by: Pantelis Antoniou <pantelis.antoniou@...sulko.com>
>> ---
>> Documentation/devicetree/overlay-notes.txt | 13 +++++++++++++
>> 1 file changed, 13 insertions(+)
>> 
>> diff --git a/Documentation/devicetree/overlay-notes.txt b/Documentation/devicetree/overlay-notes.txt
>> index d418a6c..dd595e6 100644
>> --- a/Documentation/devicetree/overlay-notes.txt
>> +++ b/Documentation/devicetree/overlay-notes.txt
>> @@ -100,6 +100,10 @@ Finally, if you need to remove all overlays in one-go, just call
>> of_overlay_destroy_all() which will remove every single one in the correct
>> order.
>> 
>> +If your board has multiple slots/places where a single overlay can work
>> +and each slot is defined by a node, you can use the of_overlay_create_indirect()
>> +method to select the target.
>> +
>> Overlay DTS Format
>> ------------------
>> 
>> @@ -113,6 +117,11 @@ The DTS of an overlay should have the following format:
>>                target=<phandle>;       /* phandle target of the overlay */
>>        or
>>                target-path="/path";    /* target path of the overlay */
> 
> Why not just let these take multiple values and the user just selects index?
> 

Implementation details. Usually there’s a descriptive label used for each
different target point. It could be a slot# or it could be a label…

A string selector maps better IMO.


>> +       or
>> +               target-indirect {       /* indirect target selector */
>> +                       foo { target|target-path ... };
>> +                       bar { .... };
>> +               };
>> 
>>                __overlay__ {
>>                        property-a;     /* add property-a to the target */
>> @@ -131,3 +140,7 @@ 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.
>> +
>> +The indirect target requires the use of a selector target on the call to
>> +of_overlay_create_indirect(). I.e. passing the "foo" id will select the target
>> +in the foo node, "bar" in bar node, etc.
>> --
>> 1.7.12
>> 

Regards

— Pantelis