linux-kernel - Re: [PATCH 03/11] dt-bindings: bus: document the stm32 debug bus

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Message-ID: <a4e11134-3035-4963-a434-db168da32945@kernel.org>
Date: Sun, 11 Jan 2026 12:27:41 +0100
From: Krzysztof Kozlowski <krzk@...nel.org>
To: Gatien Chevallier <gatien.chevallier@...s.st.com>,
 Suzuki K Poulose <suzuki.poulose@....com>, Mike Leach
 <mike.leach@...aro.org>, James Clark <james.clark@...aro.org>,
 Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
 Conor Dooley <conor+dt@...nel.org>,
 Mathieu Poirier <mathieu.poirier@...aro.org>, Leo Yan <leo.yan@...ux.dev>,
 Clément Le Goffic <legoffic.clement@...il.com>,
 Linus Walleij <linusw@...nel.org>,
 Maxime Coquelin <mcoquelin.stm32@...il.com>,
 Alexandre Torgue <alexandre.torgue@...s.st.com>
Cc: coresight@...ts.linaro.org, linux-arm-kernel@...ts.infradead.org,
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-gpio@...r.kernel.org, linux-stm32@...md-mailman.stormreply.com
Subject: Re: [PATCH 03/11] dt-bindings: bus: document the stm32 debug bus

On 09/01/2026 11:55, Gatien Chevallier wrote:
> Document the stm32 debug bus. The debug bus is responsible for
> checking the debug sub-system accessibility before probing any related
> drivers.
> 
> Signed-off-by: Gatien Chevallier <gatien.chevallier@...s.st.com>
> ---
>  .../bindings/bus/st,stm32mp131-dbg-bus.yaml        | 86 ++++++++++++++++++++++
>  1 file changed, 86 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/bus/st,stm32mp131-dbg-bus.yaml b/Documentation/devicetree/bindings/bus/st,stm32mp131-dbg-bus.yaml
> new file mode 100644
> index 000000000000..68bdfba08909
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/bus/st,stm32mp131-dbg-bus.yaml
> @@ -0,0 +1,86 @@
> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/bus/st,stm32mp131-dbg-bus.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: STM32 Coresight bus
> +
> +maintainers:
> +  - Gatien Chevallier <gatien.chevallier@...s.st.com>
> +
> +description: |


Do not need '|' unless you need to preserve formatting.

> +  The STM32 debug bus is in charge of checking the debug configuration

What sort of bus it is? What protocol? Looks like rather fake wrapping
node. You cannot just organize children in MMIO and call it a "bus".
just to justify having child nodes.

> +  of the platform before probing the peripheral drivers that rely on the debug
> +  domain.
> +
> +properties:
> +  compatible:
> +    oneOf:

Drop

> +      - items:

Drop

> +          - enum:
> +              - st,stm32mp131-dbg-bus
> +              - st,stm32mp151-dbg-bus
> +
> +  "#address-cells":
> +    const: 1
> +
> +  "#size-cells":
> +    const: 1
> +
> +  clocks:
> +    maxItems: 1
> +
> +  ranges: true
> +
> +  reg:
> +    maxItems: 1

What stuff is here? Your driver does not use it at all.

> +
> +  "#access-controller-cells":
> +    const: 1
> +    description:
> +      Contains the debug profile necessary to access the peripheral.
> +
> +patternProperties:
> +  "^.*@[0-9a-f]+$":
> +    description: Debug related peripherals
> +    type: object
> +
> +    additionalProperties: true
> +
> +    required:
> +      - access-controllers

I don't get why children need to reference the parent. If you have such
relationship, then the access-controllers are redundant, no?

> +
> +required:
> +  - "#access-controller-cells"
> +  - "#address-cells"
> +  - "#size-cells"
> +  - clocks
> +  - compatible
> +  - ranges
> +  - reg
> +
> +additionalProperties: false
> +
> +examples:
> +  - |
> +    #include <dt-bindings/clock/stm32mp1-clks.h>
> +
> +    dbg_bus: bus@...80000 {
> +      compatible = "st,stm32mp131-dbg-bus";
> +      reg = <0x50080000 0x3f80000>;
> +      #address-cells = <1>;
> +      #size-cells = <1>;
> +      clocks = <&rcc CK_DBG>;

So the same clock as child? Another argument that this node is not a
true bus node.

> +      #access-controller-cells = <1>;
> +      ranges;
> +
> +      cs_cti_trace: cti@...94000 {

Drop unused label

> +        compatible = "arm,coresight-cti", "arm,primecell";
> +        reg = <0x50094000 0x1000>;
> +        clocks = <&rcc CK_DBG>;
> +        clock-names = "apb_pclk";
> +        access-controllers = <&dbg_bus 0>;
> +        status = "disabled";

Drop

> +      };
> +    };
> 


Best regards,
Krzysztof