linux-kernel - Re: [PATCH 0/5] provide the XTAL clock via OF on Meson8/8b/8m2

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Date:   Mon, 23 Sep 2019 11:29:01 +0200
From:   Jerome Brunet <jbrunet@...libre.com>
To:     Martin Blumenstingl <martin.blumenstingl@...glemail.com>,
        narmstrong@...libre.com, robh+dt@...nel.org, mark.rutland@....com,
        linux-amlogic@...ts.infradead.org, devicetree@...r.kernel.org,
        khilman@...libre.com
Cc:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-clk@...r.kernel.org,
        Martin Blumenstingl <martin.blumenstingl@...glemail.com>
Subject: Re: [PATCH 0/5] provide the XTAL clock via OF on Meson8/8b/8m2

On Sat 21 Sep 2019 at 17:12, Martin Blumenstingl <martin.blumenstingl@...glemail.com> wrote:

> So far the HHI clock controller has been providing the XTAL clock on
> Amlogic Meson8/Meson8b/Meson8m2 SoCs.
> This is not correct because the XTAL is actually a crystal on the
> boards and the SoC has a dedicated input for it.
>
> This updates the dt-bindings of the HHI clock controller and defines
> a fixed-clock in meson.dtsi (along with switching everything over to
> use this clock).
> The clock driver needs three updates to use this:
> - patch #2 uses clk_hw_set_parent in the CPU clock notifier. This drops
>   the explicit reference to CLKID_XTAL while at the same time making
>   the code much easier (thanks to Neil for providing this new method
>   as part of the G12A CPU clock bringup!)
> - patch #3 ensures that the clock driver doesn't rely on it's internal
>   XTAL clock while not losing support for older .dtbs that don't have
>   the XTAL clock input yet
> - with patch #4 the clock controller's own XTAL clock is not registered
>   anymore when a clock input is provided via OF
>
> This series is a functional no-op. It's main goal is to better represent
> how the actual hardware looks like.

I'm a bit unsure about this series.

On one hand, I totally agree with you ... having the xtal in DT is the
right way to do it ... when done from the start

On the other hand, things have been this way for years, they are working
and going for xtal in DT does not solve any pending issue. Doing this
means adding complexity in the driver to support both methods. It is
also quite a significant change in DT :/

I'll defer this one to Kevin

>
>
> Martin Blumenstingl (5):
>   dt-bindings: clock: meson8b: add the clock inputs
>   clk: meson: meson8b: use clk_hw_set_parent in the CPU clock notifier
>   clk: meson: meson8b: change references to the XTAL clock to use the
>     name
>   clk: meson: meson8b: don't register the XTAL clock when provided via
>     OF
>   ARM: dts: meson: provide the XTAL clock using a fixed-clock
>
>  .../bindings/clock/amlogic,meson8b-clkc.txt   |   5 +
>  arch/arm/boot/dts/meson.dtsi                  |   7 ++
>  arch/arm/boot/dts/meson6.dtsi                 |   7 --
>  arch/arm/boot/dts/meson8.dtsi                 |  15 +--
>  arch/arm/boot/dts/meson8b-ec100.dts           |   2 +-
>  arch/arm/boot/dts/meson8b-mxq.dts             |   2 +-
>  arch/arm/boot/dts/meson8b-odroidc1.dts        |   2 +-
>  arch/arm/boot/dts/meson8b.dtsi                |  15 +--
>  drivers/clk/meson/meson8b.c                   | 106 +++++++++---------
>  9 files changed, 87 insertions(+), 74 deletions(-)
>
> -- 
> 2.23.0