linux-kernel - Re: [PATCH AUTOSEL 5.16 02/52] clk: samsung: exynos850: Register clocks early

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Date:   Mon, 17 Jan 2022 21:18:43 +0200
From:   Sam Protsenko <semen.protsenko@...aro.org>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...onical.com>
Cc:     Sasha Levin <sashal@...nel.org>, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org,
        Sylwester Nawrocki <s.nawrocki@...sung.com>,
        tomasz.figa@...il.com, cw00.choi@...sung.com,
        mturquette@...libre.com, sboyd@...nel.org, matthias.bgg@...il.com,
        linux-samsung-soc@...r.kernel.org, linux-clk@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org
Subject: Re: [PATCH AUTOSEL 5.16 02/52] clk: samsung: exynos850: Register
 clocks early

On Mon, 17 Jan 2022 at 19:11, Krzysztof Kozlowski
<krzysztof.kozlowski@...onical.com> wrote:
>
> On 17/01/2022 17:58, Sasha Levin wrote:
> > From: Sam Protsenko <semen.protsenko@...aro.org>
> >
> > [ Upstream commit bcda841f9bf2cddcf2f000cba96f2e27f6f2bdbf ]
> >
> > Some clocks must be registered before init calls. For example MCT clock
> > (from CMU_PERI) is needed for MCT timer driver, which is registered
> > with TIMER_OF_DECLARE(). By the time we get to core_initcall() used for
> > clk-exynos850 platform driver init, it's already too late. Inability to
> > get "mct" clock in MCT driver leads to kernel panic, as functions
> > registered with *_OF_DECLARE() can't do deferred calls. MCT timer driver
> > can't be fixed either, as it's acting as a clock source and it's
> > essential to register it in start_kernel() -> time_init().
> >
> > Let's register CMU_PERI clocks early, using CLK_OF_DECLARE(). CMU_TOP
> > generates clocks needed for CMU_PERI, but it's already registered early.
> >
> > While at it, let's cleanup the code a bit, by extracting everything
> > related to CMU initialization and registration to the separate function.
> >
> > Similar issue was discussed at [1] and addressed in commit 1f7db7bbf031
> > ("clk: renesas: cpg-mssr: Add early clock support"), as well as in
> > drivers/clk/mediatek/clk-mt2712.c.
> >
> > [1] https://patchwork.kernel.org/project/linux-renesas-soc/patch/20180829132954.64862-2-chris.brandt@renesas.com/
> >
> > Signed-off-by: Sam Protsenko <semen.protsenko@...aro.org>
> > Signed-off-by: Sylwester Nawrocki <s.nawrocki@...sung.com>
> > Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@...onical.com>
> > Link: https://lore.kernel.org/r/20211122144206.23134-1-semen.protsenko@linaro.org
> > Signed-off-by: Sasha Levin <sashal@...nel.org>
> > ---
> >  drivers/clk/samsung/clk-exynos850.c | 70 ++++++++++++++++++++---------
> >  1 file changed, 49 insertions(+), 21 deletions(-)
> >
>
> I propose to skip this one.
>
> Backporting it to v5.16 does not hurt but also does not bring any
> benefits for the upstream kernel users. There is no support for
> mentioned Exynos850 in v5.16.
>
> It could have only meaning for some downstream, out-of-tree kernels
> which apply Exynos850 support on top of v5.16, but then they can just
> take this patch as well.
>

Agreed. DTS patches will be merged only in v5.17, hopefully. Till that
time the whole clock driver is floating with no users. That's
historical thing -- I didn't have "Ack" to submit board dts at the
time, and SoC dts couldn't be applied without users (board dts). So I
focused on driver work, isolated. Not much sense to backport something
without having real users.

>
> Best regards,
> Krzysztof