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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:     Sergey Suloev <ssuloev@orpaltech.com>
Cc:     Maxime Ripard <maxime.ripard@bootlin.com>,
        devicetree@vger.kernel.org, David Airlie <airlied@linux.ie>,
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        Thierry Reding <thierry.reding@gmail.com>,
        linux-arm-kernel@lists.infradead.org
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From:   Giulio Benetti <giulio.benetti@micronovasrl.com>
Message-ID: <f8a35f86-80e5-c183-10ad-63e7425e75c6@micronovasrl.com>
Date:   Sat, 5 May 2018 00:05:00 +0200
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Hi Sergey,

Il 04/05/2018 23:59, Sergey Suloev ha scritto:
> Hi, Giulio,
> 
> On 05/05/2018 12:52 AM, Giulio Benetti wrote:
>> 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!
>>
> I'd highly recommend you to look at Armbian overlay support: it is easy 
> and elegant.
> 
> https://github.com/armbian/build/blob/master/patch/kernel/sunxi-next/add-overlay-compilation-support.patch 
> 
> 
> https://github.com/armbian/build/blob/master/patch/kernel/sunxi-next/add-sunxi-overlays.patch 

Thanks for pointing me that,
but as we've discussed before, at the moment overlays are not going to 
be included in Mainline Kernel(Maxime correct if I'm wrong).
Try to think maintaining thousands and thousands of overlays,
it would be a nightmare(IMHO).
Maybe it will change, I don't know.

Thanks anyway.
Best regards

-- 
Giulio Benetti
CTO

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