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Subject: Re: [PATCH 7/7] ARM: dts: sun7i: Add dts file for the A20-linova1-7
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To:     Maxime Ripard <maxime.ripard@bootlin.com>
Cc:     Thierry Reding <thierry.reding@gmail.com>,
        David Airlie <airlied@linux.ie>, Chen-Yu Tsai <wens@csie.org>,
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From:   Giulio Benetti <giulio.benetti@micronovasrl.com>
Message-ID: <afc78821-2d08-3f4f-d008-5b2d216e96c0@micronovasrl.com>
Date:   Fri, 4 May 2018 23:52:59 +0200
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Hi Maxime!

Il 04/05/2018 10:06, Maxime Ripard ha scritto:
> Hi,
> 
> On Wed, May 02, 2018 at 06:41:34PM +0200, Giulio Benetti wrote:
>>>> You don't have to handcode the fragments anymore with the new syntax,
>>>> and U-Boot makes it really trivial to use if you use the FIT image
>>>> format to have multiple overlays bundled in the same image. You can
>>>> choose to apply them dynamically, for example based on an EEPROM or
>>>> some other metric to see which combination you have.
>>>
>>> Ah, this is interesting. I'm going to experiment with that.
>>>
>>
>> I'm struggling against this, I don't really know how to proceed,
>> except keeping monolithic dts files including other dtsi files.
>>
>> About dt-overlays I've tried to look around lot of time,
>> but the only thing I've found is this:
>> https://git.kernel.org/pub/scm/linux/kernel/git/geert/renesas-drivers.git/tree/arch/arm/boot/dts?h=topic/renesas-overlays
>>
>> where they use .dtso tagging them as "/plugin/;"
>> and compile all .dtso found in dts folder.
>> Then they obtain .dtbo files that should be the dt-overlays we have spoken
>> about right?
> 
> Yes. You don't have to do that though, you can just rely on dtc to
> compile them, outside of the linux build system.
> 
>> What I can't understand is if there's a real standard at this time to
>> follow, because on renesas-driver they use their way to handle all .dtso
>> files, but on mainline there seems to be nothing about that.
> 
> I'm not sure what you mean here. It's just fragments of device tree,
> that have to be compiled using dtc, that's it. You can use the Linux
> build system infrastructure to do that, or you can build your own
> simpler one. That's really up to you. See for example
> https://github.com/NextThingCo/CHIP-dt-overlays/blob/master/Makefile
> 
> (even though the overlays themselves use the legacy syntax and
> shouldn't really be used an examples)

Everything works now!
Thank you very much!
I've setted up a Repo on Github to give an example on how make it work 
with no pain:
https://github.com/micronovasrl/linova-dtoverlays

At the moment it's a mess all around, but it's working and give an idea 
on how to make it work. Though I'm going to clean it up well as a base 
for linova dtoverlays.

Ah, btw, can you confirm me that base dts file must be compiled outside 
kernel with:
dtc -@ ....
Otherwise as in-tree dts with make dtbs "-@" argument is not passed.
Right?

Thank you a lot for your help and time again!

Best regards!

-- 
Giulio Benetti
CTO

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