Re: [PATCH v6 11/21] dt-bindings: clock: Add StarFive JH7110 system clock and reset generator

[Conor Dooley]

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@xxxxxxxx>
> >> 
> >> 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@xxxxxxxxxxxxx>
> >> Reviewed-by: Rob Herring <robh@xxxxxxxxxx>
> >> Signed-off-by: Emil Renner Berthing <kernel@xxxxxxxx>
> >> Signed-off-by: Hal Feng <hal.feng@xxxxxxxxxxxxxxxx>
> >> ---
> >>  .../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@xxxxxxxx>
> >> +
> >> +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.
> 
> 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.
> 
> 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?

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