Re: [RFC PATCH v2 6/7] dt-bindings: arm: mediatek: Remove SKU specific compatibles for Google Krane

[Doug Anderson]

Hi,

On Fri, Nov 10, 2023 at 1:04 PM Rob Herring <robh@xxxxxxxxxx> wrote:
>
> On Thu, Nov 09, 2023 at 06:06:03PM +0800, Chen-Yu Tsai wrote:
> > In cases where the same Chromebook model is manufactured with different
> > components (MIPI DSI panels, MIPI CSI camera sensors, or trackpad /
> > touchscreens with conflicting addresses), a different SKU ID is
> > allocated to each specific combination. This SKU ID is exported by the
> > bootloader into the device tree, and can be used to "discover" which
> > combination is present on the current machine. Thus we no longer have
> > to specify separate compatible strings for each of them.
>
> You just broke an existing kernel with a new DT having this change.
>
> Just because you come up with a new way to do things, doesn't mean you
> can remove the old way.

I was wondering about that, actually. My understanding was that what
Chen-Yu was doing here was correct, but I'm happy to be educated.

Specifically, I think that after his series old device trees will
continue to boot just fine. ...so if someone took a device tree from
before his series and booted it on a kernel after his series that
everything would be hunky dory. If that doesn't work then, I agree,
that should be fixed.

However, here, he is documenting what the "latest and greatest" device
tree should look at and that matches what's checked into the "dts"
directory. In general, I thought that yaml files didn't necessarily
always document old/deprecated ways of doing things and just focused
on documenting the new/best way.

Now, obviously, if someone took a new device tree and tried to put it
on an old kernel then it wouldn't work, but I was always under the
impression that wasn't a requirement.


-Doug