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

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Date:   Thu, 23 Feb 2023 16:26:19 +0000
From:   Krishna Yarlagadda <kyarlagadda@...dia.com>
To:     Rob Herring <robh+dt@...nel.org>
CC:     "broonie@...nel.org" <broonie@...nel.org>,
        "peterhuewe@....de" <peterhuewe@....de>,
        "jgg@...pe.ca" <jgg@...pe.ca>,
        "jarkko@...nel.org" <jarkko@...nel.org>,
        "krzysztof.kozlowski+dt@...aro.org" 
        <krzysztof.kozlowski+dt@...aro.org>,
        "linux-spi@...r.kernel.org" <linux-spi@...r.kernel.org>,
        "linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
        "linux-integrity@...r.kernel.org" <linux-integrity@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "thierry.reding@...il.com" <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Sowjanya Komatineni <skomatineni@...dia.com>,
        Laxman Dewangan <ldewangan@...dia.com>
Subject: RE: [Patch V2 3/4] spi: dt-bindings: Add Tegra TPM wait polling flag

> -----Original Message-----
> From: Rob Herring <robh+dt@...nel.org>
> Sent: 04 February 2023 01:20
> 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; Jonathan Hunter <jonathanh@...dia.com>;
> Sowjanya Komatineni <skomatineni@...dia.com>; Laxman Dewangan
> <ldewangan@...dia.com>
> Subject: Re: [Patch V2 3/4] spi: dt-bindings: Add Tegra TPM wait polling flag
> 
> External email: Use caution opening links or attachments
> 
> 
> 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
QSPI is a multi-chip-select controller and HW wait polling is only for TPM
Both controller and device would need a flag/setting to identify support
for this feature. Using SPI controller flags and SPI device mode flags to
avoid device tree flags. Moved HW/alternate TPM flow control into existing
driver. No need of new compatible now.

KY