Re: [Ksummit-discuss] Devicetree Workshop at Kernel Summit Prague (26 Oct 2017)

[Alexandre Torgue <alexandre.torgue@st.com>]

Hi Rob,

On 10/19/2017 01:53 AM, Rob Herring wrote:
> On Wed, Oct 18, 2017 at 6:28 PM, Andrew Turner <andrew@fubar.geek.nz> wrote:
>>
>>> On 18 Oct 2017, at 18:59, Tom Rini <trini@konsulko.com> wrote:
>>>
>>> On Wed, Oct 18, 2017 at 12:09:58PM +0100, Mark Brown wrote:
>>>> On Wed, Oct 18, 2017 at 06:35:24PM +0800, Chen-Yu Tsai wrote:
>>>>
>>>>> I'd like to add something on the topic of non-Linux projects. In this
>>>>> case it's diverging DT bindings from U-boot:
>>>>
>>>>> https://patchwork.ozlabs.org/patch/823158/
>>>>
>>>>> U-boot already has a set of devicetree binding additions:
>>>>> https://github.com/u-boot/u-boot/tree/master/doc/device-tree-bindings
>>>>
>>>>> The patch in question wants to ab(use) the regulator-name property for
>>>>> driver instance binding. In my opinion this is not going to fly, as
>>>>> boards are free to define the names. This either sees no use other than
>>>>> as a dirty workaround for dts files that aren't following the PMIC
>>>>> regulator bindings (regulator node names should follow well defined,
>>>>> identifying names), or results in divergence of the DT files.
>>>>
>>>> One meta issue I'm seeing here is that the u-boot people appear to have
>>>> their own divergent copy of some of the binding documents.
>>>
>>> Putting on my U-Boot hat now, it's mostly unintentional and something in
>>> general (yes, the initial topic here is not such an example) we try and
>>> avoid, or use u-boot, as the prefix on as it's something that had been
>>> previously rejected or deemed inappropriate to be in the upstream
>>> version of the binding.
>>>
>>> But perhaps it's time to try and force the issue again, given what Rob
>>> and others have said in other parts of the thread.
>>
>>  From the FreeBSD perspective I’d like it if there was a common repo for all devicetree consumers to share. We are trying to not have FreeBSD specific properties as this has caused issues in the past where we had (and still have) FreeBSD specific dts files. We are trying to remove these as drivers are updated to handle the common bindings.
> 
> Are you aware of this repo[1]? I don't have a sense for how widely
> used it is. If not, it is intended to provide a common repository of
> binding docs and dts files. If so, what are your issues with using it?
> It's generated from the kernel tree with git-filter-branch and through
> the kernel tree is the only way to add things currently. But there's
> no requirement that you add a Linux driver to submit a binding or dts
> change. We could consider taking patches against the tree directly,
> and the maintainers (me) can fixup the paths and apply to the kernel
> tree.
> 
> If there's bindings in the kernel tree you think are crap and Linux
> specific, I'd like to know that too. We should start flagging those.
> 
>> I have also spoken with some NetBSD and OpenBSD developers. They are both using devicetree to handle device enumeration. Having all 5 projects using a common set of dts files and binding would simplify keeping them in sync.
> 
> There's more than 5 likely: linux, 3x BSD, u-boot, barebox, zephyr,
> ARM trusted firmware?, UEFI?, ?

First, sorry to come late in this discussion (please be tolerant if you 
already respond to following requests/interrogations in precedent mails 
:)). From STmicro point of view we have the same kind of requests/needs 
than Andrew. We think about the possibility to use same DTS files for 
Linux, U-boot, ATF and Zephir (others could come with other vendors). 
Currently our main concerns about this are:

1-How to reduce dtb size:
	--> Reading some thread, you already start this task with Nicolas. Does 
it concerns only XiP system ?
	-->For example, I want to use the same dtsi files between Linux and 
U-boot. If in u-boot dts file I overload several "status" entry by 
"disabled", is it possible that compiler doesn't build it ? And what 
about not used phandle ?

2- The place of DT files (sources/scripts). I see (and clone) your 
"devicetree-rebasing.git" tree, it's a good start point. Currently 
(correct me  if I'm wrong) the Kernel seems to "lead" the devicetree 
bindings and devicetree dts(i) files. By using this external repo, it 
would be maybe easier to integrate changes for other components than 
Linux Kernel ? We could have (per vendor), same dtsi files which 
describes the hardware (SoC + board) and a extra dts files (at least at 
beginning) per software components to overload nodes (to disable some 
nodes not required (see (1)), to change bindings which are different 
regarding component ...).
It will also allow to have all dt script / tools for all components at 
only one place.

Once again, sorry if I repeat things already discussed but I wanted to 
expose what STMicro has in mind for DT. It will be a good topic to 
discuss at Prague.

Regards
Alex


> 
> Rob
> 
> [1] https://git.kernel.org/pub/scm/linux/kernel/git/devicetree/devicetree-rebasing.git/
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