linux-kernel - Re: [PATCH 1/3] arm64: dts: qcom: sc7280: Add pinmux for I2S speaker and Headset

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Date:   Mon, 31 Jan 2022 10:49:06 -0800
From:   Doug Anderson <dianders@...omium.org>
To:     Srinivasa Rao Mandadapu <quic_srivasam@...cinc.com>
Cc:     Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>,
        Rohit kumar <rohitkr@...eaurora.org>,
        Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        Stephen Boyd <swboyd@...omium.org>,
        Judy Hsiao <judyhsiao@...omium.org>,
        Venkata Prasad Potturu <quic_potturu@...cinc.com>,
        Maurice Alou <malou@...gle.com>
Subject: Re: [PATCH 1/3] arm64: dts: qcom: sc7280: Add pinmux for I2S speaker
 and Headset

Hi,

On Thu, Dec 23, 2021 at 7:43 AM Srinivasa Rao Mandadapu
<quic_srivasam@...cinc.com> wrote:
>
> Add AMP enable node and pinmux for primary and secondary I2S
> for SC7280 based platforms.
>
> Signed-off-by: Srinivasa Rao Mandadapu <quic_srivasam@...cinc.com>
> Co-developed-by: Venkata Prasad Potturu <quic_potturu@...cinc.com>
> Signed-off-by: Venkata Prasad Potturu <quic_potturu@...cinc.com>
> ---
>  arch/arm64/boot/dts/qcom/sc7280-idp.dtsi | 11 +++++++
>  arch/arm64/boot/dts/qcom/sc7280.dtsi     | 55 ++++++++++++++++++++++++++++++++
>  2 files changed, 66 insertions(+)
>
> diff --git a/arch/arm64/boot/dts/qcom/sc7280-idp.dtsi b/arch/arm64/boot/dts/qcom/sc7280-idp.dtsi
> index d623d71..86f182c 100644
> --- a/arch/arm64/boot/dts/qcom/sc7280-idp.dtsi
> +++ b/arch/arm64/boot/dts/qcom/sc7280-idp.dtsi
> @@ -491,6 +491,17 @@
>  };
>
>  &tlmm {
> +       amp_en: amp-en {
> +               pinmux {
> +                       pins = "gpio63";
> +                       function = "gpio";
> +               };
> +               pinconf {
> +                       pins = "gpio63";
> +                       bias-pull-down;
> +               };

Please don't split up "pinmux" and "pinconf" into two nodes anymore.
This was done in old SoCs but it's not the new style. Also:
* Having a pull-down for outputs doesn't make sense, does it?
* Should be specifying a drive strength, right?

So it should be:

amp_en: amp-en {
  pins = "gpio63";
  function = "gpio";
  bias-disable;
  drive-strength = <2>;
};


> diff --git a/arch/arm64/boot/dts/qcom/sc7280.dtsi b/arch/arm64/boot/dts/qcom/sc7280.dtsi
> index 937c2e0..b5ebc9ec 100644
> --- a/arch/arm64/boot/dts/qcom/sc7280.dtsi
> +++ b/arch/arm64/boot/dts/qcom/sc7280.dtsi
> @@ -3461,6 +3461,61 @@
>                                 };
>                         };
>
> +                       pri_mi2s_active: primary_mi2s_active {
> +                               sclk {
> +                                       pins = "gpio97";
> +                                       function = "mi2s0_sck";
> +                                       drive-strength = <16>;

A few problems:

1. drive-strength shouldn't be in the sc7280.dtsi file. That's a board
property and should be specified in the board.

2. drive-strength=16 is likely way too strong. On one sc7280 board,
our EE measured the signal and said "The AP is driving I2S lines to
[...] codec way too hard (the overshoot will damage the codec long
term).". Are you sure you need 16?

3. Node names should have dashes, not underscores.

4. I guess it's up to Bjorn, but I don't see the huge benefit of
grouping in an overarching node like this.

5. I don't know that we need the "active" there.

6. Not sure why "mclk" is down by its lonesome.

7. In general, pins should be sorted alphabetically.

So overall, I'd prefer this in the SoC dtsi file:

  pri_mi2s_data0: pri-mi2s-data0 {
    pins = "gpio98";
    function = "mi2s0_data0";
  }

  pri_mi2s_data1: pri-mi2s-data1 {
    pins = "gpio99";
    function = "mi2s0_data1";
  }

  pri_mi2s_mclk: pri-mi2s-mclk {
    pins = "gpio96";
    function = "pri_mi2s";
  };

  pri_mi2s_sclk: pri-mi2s-sclk {
    pins = "gpio97";
    function = "mi2s0_sck";
  }

  pri_mi2s_ws: pri-mi2s-ws {
    pins = "gpio100";
    function = "mi2s0_ws";
  }

Then the board file would have:

&pri_mi2s_data0 {
  drive-strength = <some_number_probably_not_16>;
  bias-something;
};

&pri_mi2s_data1 {
  drive-strength = <some_number_probably_not_16>;
  bias-something;
};

&pri_mi2s_mclk {
  drive-strength = <some_number_probably_not_16>;
  bias-something;
};

&pri_mi2s_sclk {
  drive-strength = <some_number_probably_not_16>;
  bias-something;
};

&pri_mi2s_ws {
  drive-strength = <some_number_probably_not_16>;
  bias-something;
};


> +                       sec_mi2s_active: sec-mi2s-active {
> +                               sclk {
> +                                       pins = "gpio106";
> +                                       function = "mi2s1_sck";
> +                                       drive-strength = <16>;
> +                                       bias-disable;
> +                                       output-high;
> +                               };

Similar issues for the "sec" i2s bus, but you've also got this
"output-high". Are you sure you need that?