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From:   Emil Renner Berthing <emil.renner.berthing@canonical.com>
Date:   Fri, 24 Mar 2023 10:39:36 +0100
Message-ID: <CAJM55Z-dKKpBJAof1cuAombBFckEhvZ00o6MZHT_KN+baKRc0g@mail.gmail.com>
Subject: Re: [PATCH v6 11/21] dt-bindings: clock: Add StarFive JH7110 system
 clock and reset generator
To:     Conor Dooley <conor.dooley@microchip.com>
Cc:     Hal Feng <hal.feng@starfivetech.com>,
        Conor Dooley <conor@kernel.org>, linux-clk@vger.kernel.org,
        devicetree@vger.kernel.org, linux-riscv@lists.infradead.org,
        Stephen Boyd <sboyd@kernel.org>,
        Michael Turquette <mturquette@baylibre.com>,
        Philipp Zabel <p.zabel@pengutronix.de>,
        Rob Herring <robh+dt@kernel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        Albert Ou <aou@eecs.berkeley.edu>,
        Ben Dooks <ben.dooks@sifive.com>,
        Daniel Lezcano <daniel.lezcano@linaro.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Marc Zyngier <maz@kernel.org>, linux-kernel@vger.kernel.org
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Precedence: bulk

On Thu, 23 Mar 2023 at 10:02, Conor Dooley <conor.dooley@microchip.com> wrote:
>
> Hal, Emil,
>
> On Thu, Mar 23, 2023 at 03:44:41PM +0800, Hal Feng wrote:
> > On Wed, 22 Mar 2023 21:53:37 +0000, Conor Dooley wrote:
> > > On Mon, Mar 20, 2023 at 06:37:40PM +0800, Hal Feng wrote:
> > >> From: Emil Renner Berthing <kernel@esmil.dk>
> > >>
> > >> Add bindings for the system clock and reset generator (SYSCRG) on the
> > >> JH7110 RISC-V SoC by StarFive Ltd.
> > >>
> > >> Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
> > >> Reviewed-by: Rob Herring <robh@kernel.org>
> > >> Signed-off-by: Emil Renner Berthing <kernel@esmil.dk>
> > >> Signed-off-by: Hal Feng <hal.feng@starfivetech.com>
> > >> ---
> > >>  .../clock/starfive,jh7110-syscrg.yaml         | 104 +++++++++
> > >>  MAINTAINERS                                   |   8 +-
> > >>  .../dt-bindings/clock/starfive,jh7110-crg.h   | 203 ++++++++++++++++++
> > >>  .../dt-bindings/reset/starfive,jh7110-crg.h   | 142 ++++++++++++
> > >>  4 files changed, 454 insertions(+), 3 deletions(-)
> > >>  create mode 100644 Documentation/devicetree/bindings/clock/starfive,jh7110-syscrg.yaml
> > >>  create mode 100644 include/dt-bindings/clock/starfive,jh7110-crg.h
> > >>  create mode 100644 include/dt-bindings/reset/starfive,jh7110-crg.h
> > >>
> > >> diff --git a/Documentation/devicetree/bindings/clock/starfive,jh7110-syscrg.yaml b/Documentation/devicetree/bindings/clock/starfive,jh7110-syscrg.yaml
> > >> new file mode 100644
> > >> index 000000000000..84373ae31644
> > >> --- /dev/null
> > >> +++ b/Documentation/devicetree/bindings/clock/starfive,jh7110-syscrg.yaml
> > >> @@ -0,0 +1,104 @@
> > >> +# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
> > >> +%YAML 1.2
> > >> +---
> > >> +$id: http://devicetree.org/schemas/clock/starfive,jh7110-syscrg.yaml#
> > >> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > >> +
> > >> +title: StarFive JH7110 System Clock and Reset Generator
> > >> +
> > >> +maintainers:
> > >> +  - Emil Renner Berthing <kernel@esmil.dk>
> > >> +
> > >> +properties:
> > >> +  compatible:
> > >> +    const: starfive,jh7110-syscrg
> > >> +
> > >> +  reg:
> > >> +    maxItems: 1
> > >> +
> > >> +  clocks:
> > >> +    oneOf:
> > >> +      - items:
> > >> +          - description: Main Oscillator (24 MHz)
> > >> +          - description: GMAC1 RMII reference or GMAC1 RGMII RX
> > >> +          - description: External I2S TX bit clock
> > >> +          - description: External I2S TX left/right channel clock
> > >> +          - description: External I2S RX bit clock
> > >> +          - description: External I2S RX left/right channel clock
> > >> +          - description: External TDM clock
> > >> +          - description: External audio master clock
> > >> +
> > >> +      - items:
> > >> +          - description: Main Oscillator (24 MHz)
> > >> +          - description: GMAC1 RMII reference
> > >> +          - description: GMAC1 RGMII RX
> > >> +          - description: External I2S TX bit clock
> > >> +          - description: External I2S TX left/right channel clock
> > >> +          - description: External I2S RX bit clock
> > >> +          - description: External I2S RX left/right channel clock
> > >> +          - description: External TDM clock
> > >> +          - description: External audio master clock
> > >> +
> > >> +  clock-names:
> > >> +    oneOf:
> > >> +      - items:
> > >> +          - const: osc
> > >> +          - enum:
> > >> +              - gmac1_rmii_refin
> > >> +              - gmac1_rgmii_rxin
> > >> +          - const: i2stx_bclk_ext
> > >> +          - const: i2stx_lrck_ext
> > >> +          - const: i2srx_bclk_ext
> > >> +          - const: i2srx_lrck_ext
> > >> +          - const: tdm_ext
> > >> +          - const: mclk_ext
> > >> +
> > >> +      - items:
> > >> +          - const: osc
> > >> +          - const: gmac1_rmii_refin
> > >> +          - const: gmac1_rgmii_rxin
> > >> +          - const: i2stx_bclk_ext
> > >> +          - const: i2stx_lrck_ext
> > >> +          - const: i2srx_bclk_ext
> > >> +          - const: i2srx_lrck_ext
> > >> +          - const: tdm_ext
> > >> +          - const: mclk_ext
> > >
> > > I'm sorry to be a bit of a bore about these bindings, but Emil mentioned
> > > to me today that he had some doubts about whether any of these audio
> > > clocks are actually required.
> > > I've had a bit of a look at the driver, cos the TRM that I have doesn't
> > > describe the clock tree (from what recall at least) and I think he is
> > > right.
> > > For example, the TDM clock:
> > > +   JH71X0_GATE(JH7110_SYSCLK_TDM_AHB, "tdm_ahb", 0, JH7110_SYSCLK_AHB0),
> > > +   JH71X0_GATE(JH7110_SYSCLK_TDM_APB, "tdm_apb", 0, JH7110_SYSCLK_APB0),
> > > +   JH71X0_GDIV(JH7110_SYSCLK_TDM_INTERNAL, "tdm_internal", 0, 64, JH7110_SYSCLK_MCLK),
> > > +   JH71X0__MUX(JH7110_SYSCLK_TDM_TDM, "tdm_tdm", 2,
> > > +               JH7110_SYSCLK_TDM_INTERNAL,
> > > +               JH7110_SYSCLK_TDM_EXT),
> > >
> > > Hopefully, I'm not making a balls of something here, but it looks like I
> > > can choose an internal TDM clock, that is based on JH7110_SYSCLK_MCLK,
> > > which in turn comes from either an internal or external source.
> > > If I am following correctly, that'd be:
> > > +   JH71X0__DIV(JH7110_SYSCLK_MCLK_INNER, "mclk_inner", 64, JH7110_SYSCLK_AUDIO_ROOT),
> > >
> > > Which in turn comes from:
> > > +   JH71X0__DIV(JH7110_SYSCLK_AUDIO_ROOT, "audio_root", 8, JH7110_SYSCLK_PLL2_OUT),
> > >
> > > This leaves me wondering which clocks are *actually* required for a
> > > functioning system - is it actually just osc and one of gmac1_rmii_refin
> > > or gmac1_rgmii_rxin.
> >
> > As I had mentioned somewhere before, some audio clocks need to change their
> > parents at different stages of work. I should explain in detail here.
> >
> > For the i2s*_ext clocks, we should use these external clocks as parents when
> > the I2S module is working in the slave mode, while we should use the internal
> > clocks as parents when the I2S module is working in the master mode.

Right, so what Hal is saying here is that the i2s*_ext clocks are only
needed if the board is designed to have i2s modules in slave mode.

> > For the tdm_ext clock, we use it as the clock source for an accurate playback
> > rate. If we use the internal clock as clock source, the TDM can't work
> > normally, because it can't get a required rate from the internal divider.
> > By the way, note that we need to use the internal clock as clock source when
> > we try to reset the tdm clock, otherwise, the reset will fail.
> >
> > For the mclk_ext clock, which is 12.288MHz, it's used as the clock source
> > through all the running time, otherwise, the daughter clocks can't get the
> > required rate from the internal PLL2 clock (1188MHz) through dividers.

Right, so PLL2 is 1188MHz on the VisionFive 2.

Hal: But is it not possible to program the PLL2 to run at a multiple
of 12.288MHz in some other configuration?

> > So all these audio external clocks (i2s*_ext / tdm_ext / mclk_ext) are
> > actually required.
>
> Okay. I think I am okay with leaving the binding as-is then, and if
> someone needs to omit the entire audio subsystem on the SoC, they can
> follow Stephen's suggestion.
>
> @Emil, is that okay with you?

Conor: I'm fine with the bindings like this. I just want to make sure
that we all have the same idea of what is "optional" and should be
marked as such in the bindings.

/Emil