linux-kernel - Re: [v1 1/2] dt-bindings: msm/dsi: Add 10nm dsi phy tuning properties

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Date:   Wed, 5 Jan 2022 18:07:11 -0800
From:   Stephen Boyd <swboyd@...omium.org>
To:     Rajeev Nandan <quic_rajeevny@...cinc.com>,
        devicetree@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        freedreno@...ts.freedesktop.org, linux-arm-msm@...r.kernel.org
Cc:     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, dmitry.baryshkov@...aro.org, airlied@...ux.ie,
        daniel@...ll.ch
Subject: Re: [v1 1/2] dt-bindings: msm/dsi: Add 10nm dsi phy tuning properties

Quoting Rajeev Nandan (2021-12-30 01:24:35)
> Add 10nm dsi phy tuning properties for phy drive strength and
> phy drive level adjustemnt.

s/adjustemnt/adjustment/

Please add the details about parasitics and eye shape tuning to this
commit text.

>
> Signed-off-by: Rajeev Nandan <quic_rajeevny@...cinc.com>
> ---
>  .../devicetree/bindings/display/msm/dsi-phy-10nm.yaml | 19 +++++++++++++++++++
>  1 file changed, 19 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..9406982 100644
> --- a/Documentation/devicetree/bindings/display/msm/dsi-phy-10nm.yaml
> +++ b/Documentation/devicetree/bindings/display/msm/dsi-phy-10nm.yaml
> @@ -35,6 +35,18 @@ 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
>
> +  phy-drive-strength-cfg:
> +    type: array
> +    description:
> +      Register values of DSIPHY_RESCODE_OFFSET_TOP and DSIPHY_RESCODE_OFFSET_BOT
> +      for all five lanes to adjust the phy drive strength.
> +
> +  phy-drive-level-cfg:
> +    type: array
> +    description:
> +      Register values of DSIPHY_RESCODE_OFFSET_TOP for all five lanes to adjust
> +      phy drive level/amplitude.

It would be better to put human understandable values into DT here. This
looks like a black box to anyone outside of qcom, so they won't know how
to tune or set these register values.

At least for phy-drive-level-cfg it sounds like it could be some sort of
property that is a u32 array of 5 elements for each lane indicating some
sort of amplitude, i.e.

	phy-max-amplitudes = <0 1 2 3 4>;
	phy-min-amplitudes = <0 1 2 3 4>;

where each index corresponds to a particular lane. Then the driver can
parse the amplitude and convert it into some sort of register value.