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From:   Rob Herring <robh@kernel.org>
Date:   Mon, 29 Jan 2018 08:42:08 -0600
Message-ID: <CABGGisyx_aXCxKO5x-5M5mEM7s=jMYZDaQZ9jdL6hapMCOyM=Q@mail.gmail.com>
Subject: Re: [PATCH 1/2] of: change overlay apply input data from EDT to FDT
To:     Frank Rowand <frowand.list@gmail.com>
Cc:     Rob Herring <robh+dt@kernel.org>,
        Pantelis Antoniou <pantelis.antoniou@konsulko.com>,
        Pantelis Antoniou <panto@antoniou-consulting.com>,
        devicetree@vger.kernel.org,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Geert Uytterhoeven <geert@linux-m68k.org>
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On Sun, Jan 28, 2018 at 8:53 PM,  <frowand.list@gmail.com> wrote:
> From: Frank Rowand <frank.rowand@sony.com>
>
> 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

Not really a fan of a new acronym.

> 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.
>
> of_overlay_fdt_apply() is a private function for the anticipated
> overlay loader.
>
> Update unittest.c to use of_overlay_fdt_apply() instead of
> of_overlay_apply().
>
> Move overlay fragments from artificial locations in
> drivers/of/unittest-data/tests-overlay.dtsi into one devicetree
> source file per overlay.  This led to changes in
> drivers/of/unitest-data/Makefile and drivers/of/unitest.c.

Why the rearranging? That should be a separate patch.

>
>   - Add overlay directives to the overlay devicetree source files so
>     that dtc will compile them as true overlays into one FDT data
>     chunk per overlay.

For this?

>   - Set CFLAGS for drivers/of/unittest-data/testcases.dts so that
>     symbols will be generated for overlay resolution of overlays
>     that are no longer artificially contained in testcases.dts
>
>   - Unflatten and apply each unittest overlay FDT using
>     of_overlay_fdt_apply().
>
>   - Enable the of_resolve_phandles() check for whether the overlay
>     EDT is detached.  This check was previously disabled because the
>     overlays from tests-overlay.dtsi were not unflattened into detached
>     trees.
>
>   - Other changes to unittest.c infrastructure to manage multiple test
>     FDTs built into the kernel image (access by name instead of
>     arbitrary number).
>
>   - of_unittest_overlay_high_level(): previously unused code to add
>     properties from the overlay_base devicetree to the live tree
>     was triggered by the restructuring of tests-overlay.dtsi and thus
>     testcases.dts.  This exposed two bugs: (1) the need to dup a
>     property before adding it, and (2) property 'name' is
>     auto-generated in the unflatten code and thus will be a duplicate
>     in the __symbols__ node - do not treat this duplicate as an error.
>
> Errors while developing the patch exposed inadequate error messages
> to debug problems when overlay devicetree fragment nodes contain
> an invalid target path.  Improved the messages in find_target_node().

Sounds like another separate patch.

Rob