linux-kernel - Re: ARM, SoC: About the use DT-defined properties by 3rd-party drivers

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Message-ID: <CANCZdfqZEMRaFqgph6kZPdyxBcURBiEV0XoH0vPG28Hhm5+77A@mail.gmail.com>
Date:   Mon, 12 Sep 2016 10:45:37 -0600
From:   Warner Losh <imp@...imp.com>
To:     Sebastian Frias <sf84@...oste.net>
Cc:     Mark Rutland <mark.rutland@....com>,
        devicetree <devicetree@...r.kernel.org>,
        Mason <slash.tmp@...e.fr>, Timur Tabi <timur@...i.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: ARM, SoC: About the use DT-defined properties by 3rd-party drivers

On Mon, Sep 12, 2016 at 10:29 AM, Sebastian Frias <sf84@...oste.net> wrote:
> Hi Warner,
>
> On 09/12/2016 04:26 PM, Warner Losh wrote:
>> On Mon, Sep 12, 2016 at 8:01 AM, Mark Rutland <mark.rutland@....com> wrote:
>>>> Since the question seems understood, do you have an example of other SoC's
>>>> doing something similar?
>>>
>>> I do not have an example. I know that others are using DT for data
>>> beyond what Linux or another OS requires, but it's my understanding that
>>> that is typically in a separate DTB.
>>
>> Just to clarify: FreeBSD uses, for the most part, the DTB's that the
>> 'vendor' ships, which is quite often the same ones included in Linux.
>> There's some exceptions where the bindings weren't really hardware
>> independent, or where the abstraction model was really Linux specific
>> (for things like the HDMI stack).
>>
>> However, with the advent of overlays, one would think that a vendor
>> could easily include an overlay with the DTB data for the devices they
>> don't wish to, or cannot for other reasons release. It seems like the
>> perfect mechanism to comply with the rules about inclusion of nodes in
>> the DTS. Vendors are free to document these nodes and don't require
>> the Linux kernel include them in the Documents directory to do so.
>> There have been recent efforts to move this documentation to a third
>> party to maintain.
>
> This is very interesting, do you have a more concrete example of such
> usage?

Using overlays to layer in a proprietary device blob for a proprietary driver?
No. I don't. It just seems like a natural solution. Do I have more examples
where FreeBSD has to deviate because the DT is actually Linux
specific and does a poor job of modeling the hardware and instead
reflects the Linux driver model? I have plenty of those...

Warner