linux-kernel - Re: [Patch V2 3/4] spi: dt-bindings: Add Tegra TPM wait polling flag

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Message-ID: <CAL_JsqKph2iK3Qb1=PFKxVScSs1f8sUcDh52py8WyhO6pu27TQ@mail.gmail.com>
Date:   Fri, 3 Feb 2023 13:49:32 -0600
From:   Rob Herring <robh+dt@...nel.org>
To:     Krishna Yarlagadda <kyarlagadda@...dia.com>
Cc:     broonie@...nel.org, peterhuewe@....de, jgg@...pe.ca,
        jarkko@...nel.org, krzysztof.kozlowski+dt@...aro.org,
        linux-spi@...r.kernel.org, linux-tegra@...r.kernel.org,
        linux-integrity@...r.kernel.org, linux-kernel@...r.kernel.org,
        thierry.reding@...il.com, jonathanh@...dia.com,
        skomatineni@...dia.com, ldewangan@...dia.com
Subject: Re: [Patch V2 3/4] spi: dt-bindings: Add Tegra TPM wait polling flag

On Fri, Feb 3, 2023 at 7:02 AM Krishna Yarlagadda
<kyarlagadda@...dia.com> wrote:
>
> Add "nvidia,wait-polling" flag to enable TCG TIS hardware flow control.

Tell me something that the diff doesn't.

>
> Signed-off-by: Krishna Yarlagadda <kyarlagadda@...dia.com>
> ---
>  .../bindings/spi/nvidia,tegra210-quad-peripheral-props.yaml | 6 ++++++
>  1 file changed, 6 insertions(+)
>
> diff --git a/Documentation/devicetree/bindings/spi/nvidia,tegra210-quad-peripheral-props.yaml b/Documentation/devicetree/bindings/spi/nvidia,tegra210-quad-peripheral-props.yaml
> index 2c3cada75339..19d2b30cadbf 100644
> --- a/Documentation/devicetree/bindings/spi/nvidia,tegra210-quad-peripheral-props.yaml
> +++ b/Documentation/devicetree/bindings/spi/nvidia,tegra210-quad-peripheral-props.yaml
> @@ -29,4 +29,10 @@ properties:
>      minimum: 0
>      maximum: 255
>
> +  nvidia,wait-polling:
> +    description:
> +      Enable TPM wait polling feature for QSPI as specified in TCG PC Client
> +      Specific TPM Interface Specification (TIS).
> +    $ref: /schemas/types.yaml#/definitions/flag

Why do you need this flag when you have a compatible that also
indicates you have a quirk.

If this a TPM feature, why is it enabled for every single SPI slave device?

If the fundamental issue is the controller only supports half-duplex,
why can't you just check that from the driver? Can't the SPI subsystem
tell you that the host controller is half-duplex? Though sometimes
that may be board level property I suppose. If so, define the h/w
quirk, not the driver mode in DT. Half-duplex is probably something
everyone could use, not just Nvidia.

Please discuss this series internally with the folks you marked as
maintainers. It has issues I'm sure they would have also pointed out.

Rob