linux-kernel - Re: [Patch Resend v1 5/8] dt-bindings: arm: tegra: Add NVIDIA Tegra234 CBB2.0 binding

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Date:   Thu, 16 Dec 2021 12:30:44 +0100
From:   Thierry Reding <thierry.reding@...il.com>
To:     Sumit Gupta <sumitg@...dia.com>
Cc:     linux-tegra@...r.kernel.org, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org, jonathanh@...dia.com,
        robh+dt@...nel.org, bbasu@...dia.com, vsethi@...dia.com,
        jsequeira@...dia.com
Subject: Re: [Patch Resend v1 5/8] dt-bindings: arm: tegra: Add NVIDIA
 Tegra234 CBB2.0 binding

On Thu, Dec 09, 2021 at 10:52:03PM +0530, Sumit Gupta wrote:
> Add device-tree binding documentation to represent CBB2.0 (Control
> Backbone) error handling driver. The driver prints debug information
> about failed transaction on receiving interrupt from CBB2.0.
> 
> Signed-off-by: Sumit Gupta <sumitg@...dia.com>
> ---
>  .../arm/tegra/nvidia,tegra234-cbb.yaml        | 80 +++++++++++++++++++
>  1 file changed, 80 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/arm/tegra/nvidia,tegra234-cbb.yaml
> 
> diff --git a/Documentation/devicetree/bindings/arm/tegra/nvidia,tegra234-cbb.yaml b/Documentation/devicetree/bindings/arm/tegra/nvidia,tegra234-cbb.yaml
> new file mode 100644
> index 000000000000..ad8177255e6c
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/arm/tegra/nvidia,tegra234-cbb.yaml
> @@ -0,0 +1,80 @@
> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> +%YAML 1.2
> +---
> +
> +$id: "http://devicetree.org/schemas/arm/tegra/tegra23_cbb.yaml#"
> +$schema: "http://devicetree.org/meta-schemas/core.yaml#"
> +
> +title: NVIDIA Tegra CBB2.0 Error handling driver device tree bindings
> +
> +maintainers:
> +  - Sumit Gupta <sumitg@...dia.com>
> +
> +description: |+
> +  Control Backbone (CBB) comprises of the physical path from an
> +  initiator to a target's register configuration space.
> +  CBB2.0 consists of multiple sub-blocks connected to each other
> +  to create a topology.
> +  Tegra234 SOC has different fabrics based on CBB2.0 architecture
> +  which include cluster fabrics BPMP, AON, PSC, SCE, RCE, DCE, FSI
> +  and "CBB central fabric".
> +
> +  In CBB2.0, each initiator which can issue transactions connects to
> +  a Root Master Node (MN) before it connects to any other element of
> +  the fabric. Each Root MN contains a Error Monitor (EM) which detects
> +  and logs error. Interrupts from various EM blocks are collated by
> +  Error Notifier (EN) which is per fabric and presents a single
> +  interrupt from fabric to the SOC interrupt controller.
> +
> +  The driver handles errors from CBB due to illegal register accesses
> +  and prints debug information about failed transaction on receiving
> +  the interrupt from EN. Debug information includes Error Code, Error
> +  Description, MasterID, Fabric, SlaveID, Address, Cache, Protection,
> +  Security Group etc on receiving error notification.
> +
> +  If the Error Response Disable (ERD) is set/enabled for an initiator,
> +  then SError or Data abort exception error response is masked and an
> +  interrupt is used for reporting errors due to illegal accesses from
> +  that initiator. The value returned on read failures is '0xFFFFFFFF'
> +  for compatibility with PCIE.
> +
> +properties:
> +  $nodename:
> +    pattern: "^[a-f]+-en@[0-9a-f]+$"
> +
> +  compatible:
> +    enum:
> +      - nvidia,tegra234-aon-fabric
> +      - nvidia,tegra234-bpmp-fabric
> +      - nvidia,tegra234-cbb-fabric
> +      - nvidia,tegra234-dce-fabric
> +      - nvidia,tegra234-rce-fabric
> +      - nvidia,tegra234-sce-fabric
> +
> +  reg:
> +    maxItems: 1
> +
> +  interrupts:
> +    maxItems: 1
> +    items:
> +      - description: secure interrupt from error notifier.
> +
> +  nvidia,err-notifier-base:
> +    description: address of error notifier inside a fabric.
> +
> +  nvidia,off-mask-erd:
> +    description: offset of register having ERD bit.

I was wondering about these two properties. Do we really need them? I
see that they are set on a per-SoC basic and they only differ between
the various fabrics. If they don't need to be configured on a per-board
basis, then I don't think we need to specify these explicitly. Instead I
think we could derive them from the compatible string.

Thierry

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