[PATCH v4 0/7] Properly describe mt6589 and mt8167 toprgu resets

[Luca Leonardo Scorcia]

Hi Akari,
thank you for the detailed report!

> This is somewhat outside the scope of this series, but adding TOPRGU
> reset support for MT6589 exposes a pre-existing problem with the
> mtk-wdt binding that I think should not go unnoticed.
>
> Until now, using `mediatek,mt6589-wdt` as a fallback compatible for
> other SoCs was mostly harmless, since the driver did not expose the
> TOPRGU reset controller.
> This series changes that by adding reset controller support for MT6589.

This is the exact reason that led me to touching the MT6589 code. I
have been working on improving upstream support for MT8167 and its
TOPRGU reset is required for audio support, but the current fallback
on MT6589 does not allow resets. If I changed MT8167 only, a reviewer
might have thought that the new MT8167 resets should have been applied
to MT6589 instead.
This series should cause no regressions as the addition of
#reset-cells itself only registers the reset controller for
mt6589-derived boards and it does not trigger any reset on its own.

I agree that fixing MT6589 should be an initial step and that upstream
would greatly benefit from the cleanup you described. From a
high-level standpoint it seems like all of MediaTek's WDTs include a
sw reset controller, it's just that the reset table is different for
each SoC. If I'm not mistaken, fixing it shouldn't have particular
repercussions on existing ABI since the existing fallback could be
deprecated and their compatibles relisted as independent devices, i.e.
basically what I'm doing with MT8167.

> ## MT8516
>
> According to the downstream kernel, its reset layout appears to be
> compatible with MT6589:
> [...]
> Note that a downstream kernel claiming compatibility does not necessarily
> mean that the SoCs are actually compatible. In my experience, MediaTek's
> downstream kernels contain substantial amounts of copied code between
> different SoCs, so I would not consider such compatibility claims
> sufficient evidence on their own.

Kudos for finding MT8516 sources, I have been looking for them for
ages! They actually reinforce what you say above.
MT8167 hardware is currently described upstream as MT8516 + display
blocks, but the MT8167 resets as described in the data sheet are quite
different from MT6589. That said, I've also noticed that sometimes
parts of MediaTek's data sheets are copied from other SoCs too, and
sometimes contain mistakes of their own... unless it's possible to
test on an actual device, some kind of guessing is probably
inevitable.

> I also noticed that the v3 link is missing from the cover letter:
> [3] https://lore.kernel.org/linux-arm-kernel/20260809160643.33991-1-l.scorcia@gmail.com/

Thank you for spotting this, I will list it in the next iteration!
-- 
Luca Leonardo Scorcia
l.scorcia at gmail.com