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Date:   Fri, 26 May 2023 12:39:37 +0100
From:   Conor Dooley <conor.dooley@microchip.com>
To:     Alexandre Mergnat <amergnat@baylibre.com>
CC:     Conor Dooley <conor@kernel.org>,
        Michael Turquette <mturquette@baylibre.com>,
        Stephen Boyd <sboyd@kernel.org>,
        Rob Herring <robh+dt@kernel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        Conor Dooley <conor+dt@kernel.org>,
        Matthias Brugger <matthias.bgg@gmail.com>,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@collabora.com>,
        Chen-Yu Tsai <wenst@chromium.org>,
        Markus Schneider-Pargmann <msp@baylibre.com>,
        <linux-clk@vger.kernel.org>, <devicetree@vger.kernel.org>,
        <linux-kernel@vger.kernel.org>,
        <linux-arm-kernel@lists.infradead.org>,
        <linux-mediatek@lists.infradead.org>
Subject: Re: [PATCH v2 1/2] dt-bindings: clock: mediatek: replace unusable
 clock
Message-ID: <20230526-acorn-unwound-34816283b187@wendy>
References: <20230517-fix-clk-index-v2-0-1b686cefcb7e@baylibre.com>
 <20230517-fix-clk-index-v2-1-1b686cefcb7e@baylibre.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 =E2=80=9Cmcu_pm_bclk_ck_cg=E2=80=9D clock is used by co-processor=
s and should not be
> > > added to the kernel driver, otherwise the CPU just halt and the board=
 is
> > > rebooted by the wathdog.
> > >=20
> > > Instead, add the "aes_top0_bclk_ck_cg" missing clock to prevent
> > > re-shuffling index and then preserve the ABI.
> >=20
> > How does this preserve the ABI exactly? Please describe exactly what you
> > mean by that.
>=20
> 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?
>=20
> 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
=66rom 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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