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SubjectRe: [PATCH 0/2] of: change overlay apply input data from EDT to FDT
On Mon, Jan 29, 2018 at 6:35 PM, Frank Rowand <> wrote:

Hi Frank,

> Hi Alan,
> In this patch series one of the changes was to change some
> devicetree unittest overlay source to use the new sugar syntax to
> specify overlay nodes instead of hand coding the fragment nodes.
> One reviewer reminded me to update Documentation/ files that
> show the hand coding of overlay fragment nodes. One of those
> files is Documentation/devicetree/bindings/fpga/fpga-region.txt.
> I plan to submit a patch to update the example devicetree source
> to use the sugar syntax. There is one place where I can not
> make that change, which is the "Overlay DTS Format" section.
> In this section, the use of 'target-path="/path" is shown as
> one of two ways to specify the target of the fragment. The
> sugar syntax creates a fragment using the 'target=<phandle>'
> form instead of 'target-path="/path"' form. With sugar
> syntax, there is no way to specify target-path. Is the
> target-path form needed by the fpga subsystem, or can this
> be removed?

Removing target-path won't be a loss of functionality as far as I can see.

Currently the examples in
Documentation/devicetree/bindings/fpga/fpga-region.txt all specify
'target = <phandle> while the descriptive text says that target and
target-path are both options (3 line edits are needed to remove
target-path from this file plus other edits to change it to sugar
format without __overlay__ and 'fragment@0').

Thanks for asking!


> -Frank
> On 01/29/18 16:22, Frank Rowand wrote:
>> On 01/29/18 06:08, Geert Uytterhoeven wrote:
>>> Hi Frank,
>>> On Mon, Jan 29, 2018 at 3:53 AM, <> wrote:
>>>> From: Frank Rowand <>
>>>> Move duplicating and unflattening of an overlay flattened devicetree
>>>> (FDT) into the overlay application code. To accomplish this,
>>>> of_overlay_apply() is replaced by of_overlay_fdt_apply().
>>>> The copy of the FDT (aka "duplicate FDT") now belongs to devicetree
>>>> code, which is thus responsible for freeing the duplicate FDT. The
>>>> caller of of_overlay_fdt_apply() remains responsible for freeing the
>>>> original FDT.
>>>> The unflattened device tree (aka expanded device tree, EDT) now
>>>> belongs to devicetree code, which is thus responsible for freeing
>>>> the EDT.
>>>> These ownership changes prevent early freeing of the duplicated FDT
>>>> or the EDT, which could result in use after free errors.
>>>> These changes led to migrating some unittest overlay data into
>>>> their own devicetree source files, and then converting most of
>>>> them to use sugar syntax instead of hand coding fragments.
>>> Thanks for your series!
>>>> Frank Rowand (2):
>>>> of: change overlay apply input data from EDT to FDT
>>>> of: convert unittest overlay devicetree source to sugar syntax
>>> Do you plan to update Documentation/devicetree/overlay-notes.txt
>>> and Documentation/devicetree/bindings/fpga/fpga-region.txt, too?
>> Thanks for the pointers.
>> I will add updates to Documentation/devicetree/overlay-notes.txt in
>> this series.
>> The changes to Documentation/devicetree/bindings/fpga/fpga-region.txt
>> are related to the relatively new sugar syntax in dtc, not to the
>> changes introduced by this patch series. I'll create a patch outside
>> this series to update this documentation.
>>> Gr{oetje,eeting}s,
>>> Geert
>>> --
>>> Geert Uytterhoeven -- There's lots of Linux beyond ia32 --
>>> In personal conversations with technical people, I call myself a hacker. But
>>> when I'm talking to journalists I just say "programmer" or something like that.
>>> -- Linus Torvalds

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