Re: [PATCH v2 1/2] dt-bindings: clock: mediatek: replace unusable clock

[Conor Dooley <conor.dooley@microchip.com>]

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On Fri, May 26, 2023 at 10:54:04AM +0200, Alexandre Mergnat wrote:
> On 25/05/2023 19:51, Conor Dooley wrote:
> > On Thu, May 25, 2023 at 04:50:27PM +0200, Alexandre Mergnat wrote:
> > > The “mcu_pm_bclk_ck_cg” clock is used by co-processors and should not be
> > > added to the kernel driver, otherwise the CPU just halt and the board is
> > > rebooted by the wathdog.
> > > 
> > > Instead, add the "aes_top0_bclk_ck_cg" missing clock to prevent
> > > re-shuffling index and then preserve the ABI.
> > 
> > How does this preserve the ABI exactly? Please describe exactly what you
> > mean by that.
> 
> I mean that reduce the impact of the change compared to the v1 where I've
> changed the index of the following defines to be clean.

Oh, you can't do that at all as you probably discovered!

> > Also, what about any other users of these definitions, outside of Linux?
> 
> The clock driver and bindings are only a couple of kernel versions old, I'm
> pretty sure no one is using it.

Pretty sure, or sure?

> Also, if someone use CLK_IFR_MCU_PM_BK
> define, I'm wondering how his CPU is working since Mediatek told me that
> shouldn't be used, and after some try, I confirm.

Maybe that person is actually using the index to make sure that the
clock at that index is left untouched.

> I've a question: If something is wrong in the binding, you don't fix it to
> avoid ABI change ?

I don't quite get what you mean by "wrong". These header files just
define a set of arbitrary meanings, since the clock numbers are really
just something that developers came up with rather than being lifted
from a TRM. They don't prescribe behaviour for each of these clocks, or
that these clocks should actually be used - just a simple "this number
means this clock".
It sounds more like a driver or devicetree is _using_ the number
incorrectly, but that does not make the binding wrong :)

> TBH, I just try to clean the binding. I can fix the driver index issue
> (patch 2/2) without fixing the binding if you prefer. But IMHO, keep an
> unusable define isn't great...

I, at least, would prefer that.

Thanks,
Conor.

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