linux-kernel - Re: [PATCH V7 4/6] kbuild: Add support to build overlays (%.dtbo)

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Date:   Wed, 24 Feb 2021 19:32:45 -0600
From:   Frank Rowand <frowand.list@...il.com>
To:     Rob Herring <robh@...nel.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Viresh Kumar <viresh.kumar@...aro.org>,
        Pantelis Antoniou <pantelis.antoniou@...sulko.com>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        anmar.oueja@...aro.org, Bill Mills <bill.mills@...aro.org>,
        David Gibson <david@...son.dropbear.id.au>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        linux-kbuild <linux-kbuild@...r.kernel.org>
Subject: Re: [PATCH V7 4/6] kbuild: Add support to build overlays (%.dtbo)

On 2/5/21 3:08 PM, Rob Herring wrote:
> On Fri, Feb 05, 2021 at 11:17:10AM +0100, Geert Uytterhoeven wrote:
>> Hi Viresh,
>>
>> On Fri, Feb 5, 2021 at 10:55 AM Viresh Kumar <viresh.kumar@...aro.org> wrote:
>>> On 05-02-21, 10:41, Geert Uytterhoeven wrote:
>>>> On Fri, Feb 5, 2021 at 10:25 AM Viresh Kumar <viresh.kumar@...aro.org> wrote:
>>>>> On 05-02-21, 10:02, Geert Uytterhoeven wrote:
>>>>>> Thanks for your patch
>>>>>> (which I only noticed because it appeared in dt-rh/for-next ;-)
>>>>>>
>>>>>> On Fri, Jan 29, 2021 at 8:31 AM Viresh Kumar <viresh.kumar@...aro.org> wrote:
>>>>>>> Add support for building DT overlays (%.dtbo). The overlay's source file
>>>>>>> will have the usual extension, i.e. .dts, though the blob will have
>>>>>>
>>>>>> Why use .dts and not .dtso for overlays?
>>>>>> Because you originally (until v5) had a single rule for building .dtb
>>>>>> and .dtbo files?
>>>>>
>>>>> I am fine with doing that as well if Rob and David agree to it. Rob
>>>>> did suggest that at one point but we didn't do much about it later on
>>>>> for some reason.
>>>>>
>>>>> FWIW, this will also require a change in the DTC compiler.
>>>>
>>>> Care to explain why? I've been using .dtsi for ages in
>>>> https://git.kernel.org/pub/scm/linux/kernel/git/geert/renesas-drivers.git/log/?h=topic/renesas-overlays
>>>
>>> I don't see you building them anywhere, they aren't added to the
>>> Makefile ever. What am I missing ?
>>>
>>> actually none of the dtso's were added to any makefile in that branch.
>>
>> E.g. "ARM: dts: Build all overlays if OF_OVERLAY=y"?
>> https://git.kernel.org/pub/scm/linux/kernel/git/geert/renesas-drivers.git/commit/?h=topic/renesas-overlays&id=597ee90971687a45678cca8d16bf624d174a99eb
>>
>>> Anyway, the DTC needs to know how to treat the dtso format and it will
>>> error out currently with unknown format kind of errors.
>>>
>>> Below email [1] have some information on the kind of changes required
>>> here. Also note that we had to do similar changes for dtbo earlier
>>> [2].
>>>
>>> --
>>> viresh
>>>
>>> [1] https://lore.kernel.org/lkml/CAK7LNASViCOTGR7yDTfh0O+PAu+X-P2NwdY4oPMuXrr51awafA@mail.gmail.com/
>>
>> -@ is handled by "kbuild: Enable DT symbols when CONFIG_OF_OVERLAY is used"
>> https://git.kernel.org/pub/scm/linux/kernel/git/geert/renesas-drivers.git/commit/?h=topic/renesas-overlays&id=91e9d998514f3743125a707013a30d5f83054579
>>
>>> [2] https://lore.kernel.org/lkml/30fd0e5f2156665c713cf191c5fea9a5548360c0.1609926856.git.viresh.kumar@linaro.org/
>>
>> I never had a need for those changes to dtc. .dtso/.dtbo work fine regardless.
> 
> I think what Viresh means is dtc won't automatically set the input type 
> to dts if not .dts.
> 
> We stuck with .dtbo as it's already widely used. I don't know about 
> dtso though. If there's strong consensus to use .dtso, then let's do 
> that. Whatever color for this shed you like.

I overlooked this and mistakenly thought that the move to .dtbo also
involved changing to .dtso.  My bad.

My favorite color here is to use .dtso for the source file that will
be compiled to create a .dtbo.

Linus has already accepted patch 4/6 to 5.12-rc1, so changing to .dtso
will require another patch.

-Frank

> 
> Rob
>