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Date: Fri, 10 Nov 2023 16:29:08 -0800
From: Doug Anderson <dianders@...omium.org>
To: Rob Herring <robh@...nel.org>
Cc: Chen-Yu Tsai <wenst@...omium.org>,
Frank Rowand <frowand.list@...il.com>,
Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
Conor Dooley <conor+dt@...nel.org>,
Matthias Brugger <matthias.bgg@...il.com>,
AngeloGioacchino Del Regno
<angelogioacchino.delregno@...labora.com>,
Hsin-Yi Wang <hsinyi@...omium.org>,
Dmitry Torokhov <dmitry.torokhov@...il.com>,
andriy.shevchenko@...ux.intel.com, Jiri Kosina <jikos@...nel.org>,
linus.walleij@...aro.org, broonie@...nel.org,
gregkh@...uxfoundation.org, hdegoede@...hat.com,
james.clark@....com, james@...iv.tech, keescook@...omium.org,
petr.tesarik.ext@...wei.com, rafael@...nel.org, tglx@...utronix.de,
Jeff LaBundy <jeff@...undy.com>, linux-input@...r.kernel.org,
devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
linux-mediatek@...ts.infradead.org, linux-kernel@...r.kernel.org,
Johan Hovold <johan@...nel.org>
Subject: Re: [RFC PATCH v2 6/7] dt-bindings: arm: mediatek: Remove SKU
specific compatibles for Google Krane
Hi,
On Fri, Nov 10, 2023 at 1:04 PM Rob Herring <robh@...nel.org> 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
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