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

From: [email-masked] (Sebastian Frias)
Date: Mon, 12 Sep 2016 18:29:06 +0200

Hi Warner,

On 09/12/2016 04:26 PM, Warner Losh wrote:
> On Mon, Sep 12, 2016 at 8:01 AM, Mark Rutland <[email-masked]> 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?

The overlay technique could be a solution, but so is forking and
distributing a non-documented DT. That's why I'd put this solution a
little bit lower than just exposing the entire HW description through
the DT.

Best regards,

Sebastian