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

On Mon, Sep 12, 2016 at 10:29 AM, Sebastian Frias [off-list ref] wrote:

Hi Warner,

On 09/12/2016 04:26 PM, Warner Losh wrote:

quoted

On Mon, Sep 12, 2016 at 8:01 AM, Mark Rutland [off-list ref] wrote:

quoted

quoted

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