linux-kernel - Re: [PATCH v4 01/10] dt-bindings: iommu: Add Translation Buffer Unit bindings

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Message-ID: <cfc87678-0445-42e6-9fc1-b22ef25566ff@arm.com>
Date: Mon, 12 Feb 2024 20:25:53 +0000
From: Robin Murphy <robin.murphy@....com>
To: Georgi Djakov <quic_c_gdjako@...cinc.com>, robh+dt@...nel.org,
 krzysztof.kozlowski+dt@...aro.org, conor+dt@...nel.org, will@...nel.org,
 joro@...tes.org, iommu@...ts.linux.dev
Cc: devicetree@...r.kernel.org, andersson@...nel.org,
 konrad.dybcio@...aro.org, robdclark@...il.com,
 linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
 linux-arm-msm@...r.kernel.org, quic_cgoldswo@...cinc.com,
 quic_sukadev@...cinc.com, quic_pdaly@...cinc.com, quic_sudaraja@...cinc.com,
 djakov@...nel.org
Subject: Re: [PATCH v4 01/10] dt-bindings: iommu: Add Translation Buffer Unit
 bindings

On 2024-02-01 9:05 pm, Georgi Djakov wrote:
> Add common bindings for the TBUs to describe their properties. The
> TBUs are modelled as child devices of the IOMMU and each of them is
> described with their compatible, reg and stream-id-range properties.
> There could be other implementation specific properties to describe
> any resources like clocks, regulators, power-domains, interconnects
> that would be needed for TBU operation. Such properties will be
> documented in a separate vendor-specific TBU schema.
> 
> Signed-off-by: Georgi Djakov <quic_c_gdjako@...cinc.com>
> ---
>   .../devicetree/bindings/iommu/arm,smmu.yaml   | 14 ++++++++++
>   .../devicetree/bindings/iommu/tbu-common.yaml | 28 +++++++++++++++++++
>   2 files changed, 42 insertions(+)
>   create mode 100644 Documentation/devicetree/bindings/iommu/tbu-common.yaml
> 
> diff --git a/Documentation/devicetree/bindings/iommu/arm,smmu.yaml b/Documentation/devicetree/bindings/iommu/arm,smmu.yaml
> index a4042ae24770..ba3237023b39 100644
> --- a/Documentation/devicetree/bindings/iommu/arm,smmu.yaml
> +++ b/Documentation/devicetree/bindings/iommu/arm,smmu.yaml
> @@ -235,6 +235,20 @@ properties:
>         enabled for any given device.
>       $ref: /schemas/types.yaml#/definitions/phandle
>   
> +  '#address-cells':
> +    enum: [ 1, 2 ]
> +
> +  '#size-cells':
> +    enum: [ 1, 2 ]
> +
> +  ranges: true
> +
> +patternProperties:
> +  "^tbu@[0-9a-f]+$":
> +    description: TBU child nodes
> +    type: object
> +    $ref: tbu-common.yaml#
> +
>   required:
>     - compatible
>     - reg
> diff --git a/Documentation/devicetree/bindings/iommu/tbu-common.yaml b/Documentation/devicetree/bindings/iommu/tbu-common.yaml
> new file mode 100644
> index 000000000000..3e95b356e572
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/iommu/tbu-common.yaml
> @@ -0,0 +1,28 @@
> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/iommu/tbu-common.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: Translation Buffer Unit (TBU) common properties
> +
> +maintainers:
> +  - Georgi Djakov <quic_c_gdjako@...cinc.com>
> +
> +description:
> +  The SMMU implements a TBU for system masters. It consists if a
> +  Translation Lookaside Buffer (TLB) that caches page tables.
> +
> +properties:
> +  reg:
> +    maxItems: 1
> +
> +  stream-id-range:
> +    $ref: /schemas/types.yaml#/definitions/uint32-array
> +    description: Stream ID range (address and size) that is assigned by the TBU
> +    items:
> +      minItems: 2
> +      maxItems: 2

Actually, even this doesn't work - for the 15-bit StreamID config, 
there's no guarantee that the devices behind each TBU will use a single 
contiguous StreamID range. Conversely, for any other config the 
StreamIDs are already uniquely associated with a TBU by their top 5 
bits, so the "size" doesn't matter.

Thanks,
Robin.

> +
> +additionalProperties: true
> +...