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

From: Warner Losh
Date: Mon Sep 12 2016 - 12:45:44 EST

On Mon, Sep 12, 2016 at 10:29 AM, Sebastian Frias <sf84@xxxxxxxxxxx> 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@xxxxxxx> 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...