linux-kernel - Re: [PATCH v2] dt-bindings: spi: nvidia,tegra210-quad: Add IOMMU property for Tegra234

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Message-ID: <20250514190106.GA2808529-robh@kernel.org>
Date: Wed, 14 May 2025 14:01:06 -0500
From: Rob Herring <robh@...nel.org>
To: Vishwaroop A <va@...dia.com>
Cc: krzk@...nel.org, broonie@...nel.org, krzk+dt@...nel.org,
	conor+dt@...nel.org, thierry.reding@...il.com, jonathanh@...dia.com,
	skomatineni@...dia.com, ldewangan@...dia.com,
	kyarlagadda@...dia.com, smangipudi@...dia.com,
	linux-spi@...r.kernel.org, devicetree@...r.kernel.org,
	linux-tegra@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] dt-bindings: spi: nvidia,tegra210-quad: Add IOMMU
 property for Tegra234

On Tue, May 06, 2025 at 06:08:48PM +0000, Vishwaroop A wrote:
> The Tegra210 Quad SPI controller uses internal DMA engines to efficiently
> transfer data between system memory and the SPI bus. On Tegra234 platform,
> DMA transactions must be properly mapped and protected through IOMMU to
> ensure system security and functional correctness. Tegra241 uses external
> DMA and doesn't require IOMMU.
> 
> Add the iommus property to the device tree binding, making it required
> only for Tegra234 platform while explicitly disallowing it for other
> platforms including Tegra241.
> 
> Signed-off-by: Vishwaroop A <va@...dia.com>
> ---
>  .../bindings/spi/nvidia,tegra210-quad.yaml    | 22 +++++++++++++++++++
>  1 file changed, 22 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/spi/nvidia,tegra210-quad.yaml b/Documentation/devicetree/bindings/spi/nvidia,tegra210-quad.yaml
> index 48e97e240265..ac79cb19c81a 100644
> --- a/Documentation/devicetree/bindings/spi/nvidia,tegra210-quad.yaml
> +++ b/Documentation/devicetree/bindings/spi/nvidia,tegra210-quad.yaml
> @@ -12,6 +12,25 @@ maintainers:
>  
>  allOf:
>    - $ref: spi-controller.yaml#
> +  - if:
> +      properties:
> +        compatible:

Use 'contains' here so if this is ever a fallback, it works for that 
case.

> +          enum:
> +            - nvidia,tegra234-qspi
> +    then:
> +      required:
> +        - iommus
> +  - if:
> +      properties:
> +        compatible:
> +          enum:
> +            - nvidia,tegra210-qspi
> +            - nvidia,tegra186-qspi
> +            - nvidia,tegra194-qspi
> +            - nvidia,tegra241-qspi

Shouldn't this just be an 'else'? I suppose sometimes an IOMMU might not 
be enabled, but that's policy. Either the h/w has an IOMMU or it 
doesn't.

> +    then:
> +      properties:
> +        iommus: false
>  
>  properties:
>    compatible:
> @@ -47,6 +66,9 @@ properties:
>        - const: rx
>        - const: tx
>  
> +  iommus:
> +    maxItems: 1
> +
>  patternProperties:
>    "@[0-9a-f]+$":
>      type: object
> -- 
> 2.17.1
>