linux-kernel - Re: [PATCH] devicetree: Move include prefixes from arch to separate directory

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Date:   Mon, 15 May 2017 10:52:18 -0500
From:   Rob Herring <robh+dt@...nel.org>
To:     Olof Johansson <olof@...om.net>
Cc:     Russell King - ARM Linux <linux@...linux.org.uk>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        Heiko Stuebner <heiko@...ech.de>,
        Mark Rutland <mark.rutland@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Mikael Starvik <starvik@...s.com>,
        Jesper Nilsson <jesper.nilsson@...s.com>,
        James Hogan <james.hogan@...tec.com>,
        Ralf Baechle <ralf@...ux-mips.org>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Frank Rowand <frowand.list@...il.com>,
        linux-arch <linux-arch@...r.kernel.org>
Subject: Re: [PATCH] devicetree: Move include prefixes from arch to separate directory

On Mon, May 15, 2017 at 10:27 AM, Olof Johansson <olof@...om.net> wrote:
> On Mon, May 15, 2017 at 7:47 AM, Rob Herring <robh+dt@...nel.org> wrote:
>> On Mon, May 15, 2017 at 9:26 AM, Russell King - ARM Linux
>> <linux@...linux.org.uk> wrote:
>>> On Mon, May 15, 2017 at 08:01:07AM -0500, Rob Herring wrote:
>>>> I'd prefer not to mix things in scripts/dtc that aren't the import of
>>>> dtc (yes, we do have a few other things already, but they are at least
>>>> scripts). Couldn't this go in include/dt-bindings/ instead?
>>>
>>> I don't think that works.
>>>
>>> The include path used is "include", which means that we force people
>>> to use:
>>>
>>> #include <dt-bindings/foo.dtsi>
>>
>> No, I was thinking you'd add include/dt-bindings/include-prefix/ to
>> the include path instead of scripts/dtc/include-prefix/. The only
>> downside I can see is people could mistakenly do:
>>
>> #include <dt-bindings/include-prefix/$arch/foo.dtsi>
>
> I considered that but thought it was a worse solution than the one I
> ended up with. It's just confusing to have -I paths that enter an
> include hierarchy at different levels like that.
>
> Just see what already happened with the mistake on rockchip, where
> Heiko accidentally included <include/dt-include/...> instead -- it'd
> be nice to catch that when it happens through tools
>
>>>
>>> in their DT files.  This means that we'd need to populate $topdir/include
>>> with per-architecture symlinks on top of the 26 or so directories already
>>> there, so that:
>>>
>>> #include <arch/foo.dtsi>
>>>
>>> would work.  That's quite horrible, since $topdir/include is the main
>>> include path for C headers.
>>>
>>> I guess we could have symlinks inside include/dt-bindings, but that
>>> makes the includes:
>>>
>>> #include <dt-bindings/arch/foo.dtsi>
>>>
>>> but that's rather absurd because these _aren't_ dt-binding definitions.
>>
>> True, but the same can be said that "scripts/dtc" is not includes nor
>> kernel build infrastructure.
>>
>>> Maybe what we should do is:
>>>
>>> mkdir include/dt
>>> git mv include/dt-bindings include/dt
>>> for arch in arch/*; do
>>>   dts=$arch/boot/dts
>>>   if [ -d $dts ]; then
>>>      a=include/dt/$(basename $arch)
>>>      ln -s $dts $a
>>>      git add $a
>>>   fi
>>> done
>>> ... fixup scripts/Makefile.lib ...
>>> git commit
>>
>> That would just break every existing include in dts files.
>
> It doesn't break dts includes if done together with a change in -I,
> but it might break includes from the driver side (or needs another -I
> there).

Ah yes, I should have paid attention to the mkdir.

>> Another idea. Could kbuild create all the symlinks at build time instead?
>
> I considered that, but given that we're talking about a few soft links
> that we need to find a good home for, it seemed like overkill that
> adds magic to the build process. Having somehting that is easily
> discovered when looking around the source tree is a lot better.
>
> I looked around the tree for suitable homes for this directory of
> links, and the least out-of-place I could find was under scripts/dtc.
> You even have a script for uprevving the imported dtc sources, so it's
> not like it's causing any problems from that point of view. But I do
> agree that it's not ideal -- it was just the least bad option I could
> find at the time. Better suggestions are welcome.

Fair enough. Like I said, it was only a preference and certainly not
unprecedented. I'll just get less receptive with each addition. :)

When and by whom do you propose merging this?

The only other comment I would have is at some point, we're going to
have overlays that aren't tied to any arch. Where are we going to put
those? Maybe they are tied to some vendor which tends to have most
stuff in $arch and we just continue this band-aid. Or we define some
common location. I bring this up now only because both could use that
location.

Rob