linux-kernel - Re: [v2 1/3] dt-bindings: msm/dsi: Add 10nm dsi phy tuning properties

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Message-ID: <CAA8EJprrRZK+ocW9zDY_eyeo_m_xbu+KmfWf8QmTYscAh5SxLw@mail.gmail.com>
Date:   Mon, 10 Jan 2022 17:06:03 +0300
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Rajeev Nandan <quic_rajeevny@...cinc.com>
Cc:     dri-devel@...ts.freedesktop.org, linux-arm-msm@...r.kernel.org,
        freedreno@...ts.freedesktop.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, sean@...rly.run, robdclark@...il.com,
        robh+dt@...nel.org, robh@...nel.org, quic_abhinavk@...cinc.com,
        quic_kalyant@...cinc.com, quic_mkrishn@...cinc.com,
        jonathan@...ek.ca, airlied@...ux.ie, daniel@...ll.ch,
        swboyd@...omium.org
Subject: Re: [v2 1/3] dt-bindings: msm/dsi: Add 10nm dsi phy tuning properties

On Mon, 10 Jan 2022 at 15:56, Rajeev Nandan <quic_rajeevny@...cinc.com> wrote:
>
> In most cases, the default values of DSI PHY tuning registers should be
> sufficient as they are fully optimized. However, in some cases where
> extreme board parasitics cause the eye shape to degrade, the override
> bits can be used to improve the signal quality.
>
> The general guidelines for DSI PHY tuning include:
> - High and moderate data rates may benefit from the drive strength and
>   drive level tuning.
> - Drive strength tuning will affect the output impedance and may be used
>   for matching optimization.
> - Drive level tuning will affect the output levels without affecting the
>   impedance.
>
> The clock and data lanes have a calibration circuitry feature. The drive
> strength tuning can be done by adjusting rescode offset for hstop/hsbot,
> and the drive level tuning can be done by adjusting the LDO output level
> for the HSTX drive.
>
> Signed-off-by: Rajeev Nandan <quic_rajeevny@...cinc.com>
> ---
>
> Changes in v2:
>  - More details in the commit text (Stephen Boyd)
>  - Use human understandable values (Stephen Boyd, Dmitry Baryshkov)
>  - Do not take values that are going to be unused (Dmitry Baryshkov)
>
>  .../bindings/display/msm/dsi-phy-10nm.yaml         | 33 ++++++++++++++++++++++
>  1 file changed, 33 insertions(+)
>
> diff --git a/Documentation/devicetree/bindings/display/msm/dsi-phy-10nm.yaml b/Documentation/devicetree/bindings/display/msm/dsi-phy-10nm.yaml
> index 4399715..d0eb8f6 100644
> --- a/Documentation/devicetree/bindings/display/msm/dsi-phy-10nm.yaml
> +++ b/Documentation/devicetree/bindings/display/msm/dsi-phy-10nm.yaml
> @@ -35,6 +35,35 @@ properties:
>        Connected to DSI0_MIPI_DSI_PLL_VDDA0P9 pin for sc7180 target and
>        connected to VDDA_MIPI_DSI_0_PLL_0P9 pin for sdm845 target

Generic note:
I think these properties should be prefixed with "qcom," prefix.

>
> +  phy-rescode-offset-top:
> +    $ref: /schemas/types.yaml#/definitions/uint8-array
> +    minItems: 5
> +    maxItems: 5
> +    description:
> +      Integer array of offset for pull-up legs rescode for all five lanes.
> +      To offset the drive strength from the calibrated value in an increasing
> +      or decreasing manner, use 6 bit two’s complement values.

dtc should support negative values, google hints that <(-2)> should work.

> +
> +  phy-rescode-offset-bot:
> +    $ref: /schemas/types.yaml#/definitions/uint8-array
> +    minItems: 5
> +    maxItems: 5
> +    description:
> +      Integer array of offset for pull-down legs rescode for all five lanes.
> +      To offset the drive strength from the calibrated value in an increasing
> +      or decreasing manner, use 6 bit two’s complement values.
> +
> +  phy-drive-ldo-level:
> +    $ref: /schemas/types.yaml#/definitions/uint8
> +    minimum: 0
> +    maximum: 7
> +    description:
> +      The PHY LDO has an amplitude tuning feature to adjust the LDO output
> +      for the HSTX drive. To offset the drive level from the default value,
> +      supported levels are with the following mapping:
> +      0 = 375mV, 1 = 400mV, 2 = 425mV, 3 = 450mV, 4 = 475mV, 5 = 500mV,
> +      6 = 500mV, 7 = 500mV

No encoding please. Specify the values in the dts and convert them
into the register values in the driver.

> +
>  required:
>    - compatible
>    - reg
> @@ -64,5 +93,9 @@ examples:
>           clocks = <&dispcc DISP_CC_MDSS_AHB_CLK>,
>                    <&rpmhcc RPMH_CXO_CLK>;
>           clock-names = "iface", "ref";
> +
> +         phy-resocde-offset-top = /bits/ 8 <0x0 0x0 0x0 0x0 0x0>;
> +         phy-rescode-offset-bot = /bits/ 8 <0x0 0x0 0x0 0x0 0x0>;
> +         phy-drive-ldo-level = /bits/ 8 <1>;

--
With best wishes
Dmitry