Re: [PATCH] dt-bindings: arm: qcom: drop the superfluous device compatibility schema

[Stephan Gerhold <stephan@gerhold.net>]

On Tue, Feb 20, 2024 at 11:11:15AM +0200, Dmitry Baryshkov wrote:
> On Sun, 11 Feb 2024 at 12:36, Stephan Gerhold <stephan@gerhold.net> wrote:
> > On Sun, Feb 04, 2024 at 06:56:35PM +0200, Dmitry Baryshkov wrote:
> > > The idea impressed in the commit b32e592d3c28 ("devicetree: bindings:
> > > Document qcom board compatible format") never got actually adopted. As
> > > can be seen from the existing board DT files, no device actually used
> > > the PMIC / foundry / version parts of the compatible string. Drop this
> > > compatibility string description to avoid possible confusion and keep
> > > just the generic terms and the SoC list.
> > >
> > > Fixes: b32e592d3c28 ("devicetree: bindings: Document qcom board compatible format")
> >
> > FWIW: It's not correct that no device uses the version parts of the
> > compatible string. There are actually two boards documented in qcom.yaml
> > that follow this scheme:
> >
> >   compatible = "qcom,msm8916-mtp", "qcom,msm8916-mtp/1", "qcom,msm8916";
> >   compatible = "longcheer,l8150", "qcom,msm8916-v1-qrd/9-v1", "qcom,msm8916";
> >
> > I don't think anyone is actively relying on those, though. I guess we
> > can just ignore them or even remove them.
> 
> Excuse me for the long delay. As it was you who added the
> longcheer-l8150 support, does it require any of the msm-id options or
> dtbTool (original or modified) processing?
> If it can work with no additional tags, we can drop these compatibility strings.
> 

I think we added it back then to allow booting mainline with the
original bootloader. Together with the "skales" dtbTool (used to be at
https://source.codeaurora.org/quic/kernel/skales) the compatible does
result in a correct QCDT that is accepted by the bootloader.

I doubt anyone still uses this way of booting nowadays. In postmarketOS
we strongly recommend everyone to boot MSM8916 devices using lk2nd [1]
which supports plain appended DTB without special properties and other
more reliable forms of DTB selection. I have not tested booting mainline
with the original bootloader for many years.

Dropping the extra compatible would be fine for me. Personally I don't
consider booting via weird/broken bootloaders worth supporting (at least
if better workarounds exist). Having to boot with "custom" bootloaders
tends to be a somewhat subjective topic though so others might disagree.

Thanks,
Stephan

[1]: https://github.com/msm8916-mainline/lk2nd