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From:   Linus Walleij <linus.walleij@linaro.org>
Date:   Tue, 1 Dec 2020 23:51:26 +0100
Message-ID: <CACRpkdYNL=PbWgf9wdKpiC2y1iZFG-ZD47O8u2a22zzGus9P2Q@mail.gmail.com>
Subject: Re: [BUG] SPI broken for SPI based panel drivers
To:     "H. Nikolaus Schaller" <hns@goldelico.com>
Cc:     Sven Van Asbroeck <thesven73@gmail.com>,
        Mark Brown <broonie@kernel.org>,
        kernel list <linux-kernel@vger.kernel.org>,
        Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
        Discussions about the Letux Kernel 
        <letux-kernel@openphoenux.org>,
        Andreas Kemnade <andreas@kemnade.info>
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On Tue, Dec 1, 2020 at 6:13 PM H. Nikolaus Schaller <hns@goldelico.com> wrote:

> I am not sure if DT maintainers accept that we revert a DT change just to
> handle some change in a driver. Usually they insist on fixing a driver and
> live with the DT. DT is carved in stone or could be ROM...

I usually use this rough consensus: is the DTB flashed into millions of
devices and supplied to the kernel using some bootloader, and
is the kernel upgraded on the device without also upgrading the
DTB?

And I mean in practice, not in theory.

So whether the DTB ABI can be changed or not is a practical
deployment question, not a religious sacrament. It came from systems
such as Sun machines where the DTB was, indeed, in a PROM,
and indeed intended for SunOS so Linux had no control over
it. We had to just treat it as static ABI.

If the actual situation is different, sucn as kernel and DTB are
always updated together, or those are a few custom systems in
a factory floor (not millions of mobile phones or laptops) then
it is fine to change it occasionally even if it is seen as "bad".

Yours,
Linus Walleij