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Date: Sun, 23 Aug 2015 16:52:32 -0700
Message-ID: <CAOesGMigmaEviCDBAncomkq+uowr18B5FTOmOyBHsNz4p6F6Dw@mail.gmail.com>
Subject: Re: [PATCH v5] dtb: Create a common home for cross-architecture dtsi files.
From: Olof Johansson <olof@lixom.net>
To: Rob Herring <robherring2@gmail.com>
Cc: Ian Campbell <ian.campbell@citrix.com>, "arm@kernel.org" <arm@kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Rob Herring <robh+dt@kernel.org>, Pawel Moll <pawel.moll@arm.com>,
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        Liviu Dudau <liviu.dudau@arm.com>, Sudeep Holla <sudeep.holla@arm.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
        Russell King <linux@arm.linux.org.uk>,
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On Sun, Aug 23, 2015 at 4:42 PM, Rob Herring <robherring2@gmail.com> wrote:
> On Sun, Aug 23, 2015 at 6:13 PM, Olof Johansson <olof@lixom.net> wrote:
>> On Fri, Aug 14, 2015 at 2:21 PM, Rob Herring <robherring2@gmail.com> wrote:
>>> +arm-soc
>>>
>>> On Tue, Aug 11, 2015 at 5:07 AM, Ian Campbell <ian.campbell@citrix.com> wrote:
>>>> On Mon, 2015-08-03 at 17:06 +0100, Ian Campbell wrote:
>>>>> Commit 9ccd608070b6 ("arm64: dts: add device tree for ARM SMM-A53x2 on
>>>>> LogicTile Express 20MG") added a new dts file to arch/arm64 which
>>>>> included "../../../../arm/boot/dts/vexpress-v2m-rs1.dtsi", i.e. a
>>>>> .dtsi supplied by arch/arm.
>>>>>
>>>>> Unfortunately this causes some issues for the split device tree
>>>>> repository[0], since things get moved around there. In that context
>>>>> the new .dts ends up at src/arm64/arm/vexpress-v2f-1xv7-ca53x2.dts
>>>>> while the include is at src/arm/vexpress-v2m-rs1.dtsi.
>>>>
>>>> Hi Grant,
>>>>
>>>> Do you think there is any chance of getting this into 4.2-rc$NEXT or shall
>>>> we wait until 4.3? I'm assuming this should go via the DT tree, but maybe
>>>> it should go via an ARM tree?
>>>
>>> I was assuming this would go thru the arm-soc tree which is why I
>>> acked it. It is getting a bit late for 4.2 at this point, but I guess
>>> the standalone tree remains broken for these platforms until this is
>>> done. Probably not such a big deal in grand scheme of things.
>>
>> I'm cc:d in the far tail of a thread, so I'll just comment here
>> instead of further up:
>>
>> I'm not a fan at all of creating kernel/dts/<arch>/*, at least if
>> there's expected to be contents in there.
>>
>> We don't have include/linux/asm-<arch>/ in the common tree either.
>> Let's not create that for dts.
>
> I'd really like to move ALL dts files from arch/*. There's nothing
> really tied to the architecture. They may happen to use some bindings
> that only apply to an architecture, but fundamentally they don't
> depend on the arch. Also, I'd like to be able to do "make all-dtbs"
> and build every dtb in the tree.

The main benefit of keeping it per architecture and platform is that
it partitions the maintainer and review space a bit.

Right now it's not possible to do even per-arch "all-dtbs" since only
the currently configured platforms will get their dtbs compiled.

> That said, I'm not crazy enough to propose this re-org in the kernel
> tree, but would like to do that if/when we moved dts files out of the
> kernel.

I believe this is currently still quite firmly in the "if" stage. :(

>> So, while I'm all for a prefix-based sharing of DTSI files, I don't
>> want them to go in a common kernel/dts directory.
>>
>> Besides sharing some snippets between arm and arm64, what else is
>> expected to need to go into such a shared location today?
>
> Overlays. You easily have the same sharing of common boards. There are
> also usecases of overlays on architectures that don't generally use DT
> (x86).

Ok, overlays might make sense if they can be made to work generically
enough and not be tied to expectations of the base board platform.

Still, even then I don't see dts as a core kernel feature (kernel/*),
lib/* might make more sense. And I don't want to see things like
vexpress stuff in there.

> We could also see sharing between PPC and ARM on FSL networking parts,
> but I've not heard if they actually have that problem.

Yeah, there could potentially be some sharing between MIPS and
ARM{,64} too, but I don't know if we'll actually see it done.


-Olof
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