Re: [RFC PATCH 1/3] dt-bindings: pinctrl: mt8516/mt8167: Move compatibles from mt66xx to mt6795

[Luca Leonardo Scorcia]

Hi,

> I've not done a very through analysis, but this seems like a massive ABI
> break.
> The change you're trying to make here will mean that new kernels will
> not work with older devicetrees AFAICT.

Correct, that's the reason I sent it as an RFC (I mentioned this in
the cover letter). I am new to kernel work and I'm not sure how to
deal with this change. On one hand I am almost certain now that the
upstream driver has never been used in actual devices, since the older
code was only partially merged and also, as Sashiko correctly pointed
out in [1], it had serious errors when matched against the data sheet:

Sashiko:
> Does this configuration cause a regression in pin multiplexing across the SoC?
> The legacy driver used a 4-bit shift per pin to pack 5 pins per 32-bit
> register. By passing 3 as the width here, the framework calculates mode
> offsets using 3 bits per pin. This causes pinmux writes to align with
> the wrong bits and can overwrite the configurations of adjacent pins.

Data sheet here clearly shows 3 bits per pin are used to choose the
pin function.

On the other hand I know that breaking the ABI is a big no. But what
would be an appropriate solution? Maybe duplicating the driver with a
different name, something like mediatek,mt8167-pinctrl-v2? Is there
another driver I could have a look at to learn how to approach this
problem?
Sashiko also pointed out some other minor issues with the register
maps I already fixed locally after confirming with the data sheet, but
did not provide clues about how to solve the ABI breakage.

[1] https://sashiko.dev/#/message/20260625111629.6CD701F000E9%40smtp.kernel.org

Thank you for your time!
-- 
Luca Leonardo Scorcia
l.scorcia@xxxxxxxxx