linux-kernel - Re: [PATCH 1/2] dt-bindings: timer: Add ARM SSE(Subsystems for Embedded) timer

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Message-ID: <20250822-busy-dragonfly-of-science-d769bb@kuoka>
Date: Fri, 22 Aug 2025 09:21:16 +0200
From: Krzysztof Kozlowski <krzk@...nel.org>
To: Jisheng Zhang <jszhang@...nel.org>
Cc: Daniel Lezcano <daniel.lezcano@...aro.org>, 
	Thomas Gleixner <tglx@...utronix.de>, Rob Herring <robh@...nel.org>, 
	Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, linux-kernel@...r.kernel.org, 
	devicetree@...r.kernel.org
Subject: Re: [PATCH 1/2] dt-bindings: timer: Add ARM SSE(Subsystems for
 Embedded) timer

On Thu, Aug 21, 2025 at 11:24:28PM +0800, Jisheng Zhang wrote:
> Add binding doc for the ARM SSE(Subsystems for Embedded) timer. Here
> is the document URL:
> https://developer.arm.com/documentation/107610/0000/System-timer-components?lang=en
> 
> Although the IP is mostly seen on MCU SoC platforms, but nothing
> prevent it from being integrated into linux capable SoC platforms.

But is there such integration?

> 
> The IP core may have a system counter to generate timestamp value,
> a system timer to raise an interrupt when a period has elapsed, and
> a System Watchdog to detect errant system behaviour then reset the
> system if a period elapses without ping.
> 
> Signed-off-by: Jisheng Zhang <jszhang@...nel.org>
> ---
>  .../bindings/timer/arm,sse_timer.yaml         | 90 +++++++++++++++++++
>  1 file changed, 90 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/timer/arm,sse_timer.yaml
> 
> diff --git a/Documentation/devicetree/bindings/timer/arm,sse_timer.yaml b/Documentation/devicetree/bindings/timer/arm,sse_timer.yaml
> new file mode 100644
> index 000000000000..37a79f9052d0
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/timer/arm,sse_timer.yaml
> @@ -0,0 +1,90 @@
> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/timer/arm,sse_timer.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: ARM SSE(Subsystems for Embedded) system timer
> +
> +maintainers:
> +  - Jisheng Zhang <jszhang@...nel.org>
> +
> +description: |+

Drop |+

> +  ARM SSE(Subsystems for Embedded) system timer core may have a system counter
> +  to generate timestamp value, a system timer to raise an interrupt when a
> +  period has elapsed, and a System Watchdog to detect errant system behaviour
> +  then reset the system if a period elapses without ping.
> +
> +properties:
> +  compatible:
> +    items:
> +      - enum:

Drop these two, just const.

> +          - arm,sse-timer
> +
> +  reg:
> +    maxItems: 1
> +    description: The system counter control frame base
> +
> +  clocks:
> +    maxItems: 1
> +
> +  '#address-cells':
> +    enum: [1, 2]
> +
> +  '#size-cells':
> +    const: 1
> +
> +  ranges: true
> +
> +patternProperties:
> +  '^frame@[0-9a-f]+$':
> +    type: object
> +    additionalProperties: false
> +    description: A timer node has some frame sub-nodes, each frame can be timer frame or watchdog frame. Each frame has the following properties.

Please follow Linux coding style.

> +    properties:
> +      interrupts:
> +        minItems: 1
Drop

> +        items:
> +          - description: timer irq

Drop, instead maxItems: 1

> +
> +      reg:

Keep order as in every other binding (and DTS coding style).

> +        minItems: 1
> +        items:
> +          - description: 1st view base address
> +          - description: 2nd optional view base address if this is a watchdog frame
> +
> +    required:
> +      - interrupts
> +      - reg

Keep DTS coding style order.

> +
> +required:
> +  - compatible
> +  - reg
> +  - '#address-cells'
> +  - '#size-cells'
> +
> +additionalProperties: false
> +
> +examples:
> +  - |
> +    timer@...3e000 {
> +      compatible = "arm,sse-timer";
> +      #address-cells = <1>;

Keep order as in DTS coding style.

> +      #size-cells = <1>;
> +      ranges;
> +      reg = <0xf7f3e000 0x2000>;
> +      clocks = <&core_clk>;
> +
> +      frame@...20000 {
> +        reg = <0xf7f20000 0x1000>;
> +        interrupts = <0 26 0x8>;

Use proper defines

> +      };
> +
> +      frame@...30000 {
> +        interrupts = <0 15 0x8>;
> +        reg = <0xf7f32000 0x1000>,
> +              <0xf7f33000 0x1000>;
> +      };

Best regards,
Krzysztof