linux-kernel - Re: [PATCH v3 1/2] dt-bindings: vm-wdt: Add qemu,vm-watchdog compatible

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Date:   Mon, 25 Apr 2022 13:29:51 -0500
From:   Rob Herring <robh@...nel.org>
To:     Sebastian Ene <sebastianene@...gle.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Arnd Bergmann <arnd@...db.de>,
        Dragan Cvetic <dragan.cvetic@...inx.com>,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
        maz@...nel.org, will@...nel.org, qperret@...gle.com
Subject: Re: [PATCH v3 1/2] dt-bindings: vm-wdt: Add qemu,vm-watchdog
 compatible

On Mon, Apr 25, 2022 at 01:42:05PM +0000, Sebastian Ene wrote:
> The stall detection mechanism allows to configure the expiration
> duration and the internal counter clock frequency measured in Hz.
> Add these properties in the schema.
> 
> Signed-off-by: Sebastian Ene <sebastianene@...gle.com>
> ---
>  .../devicetree/bindings/misc/vm-wdt.yaml      | 44 +++++++++++++++++++
>  1 file changed, 44 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/misc/vm-wdt.yaml
> 
> diff --git a/Documentation/devicetree/bindings/misc/vm-wdt.yaml b/Documentation/devicetree/bindings/misc/vm-wdt.yaml
> new file mode 100644
> index 000000000000..cb7665a0c5af
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/misc/vm-wdt.yaml
> @@ -0,0 +1,44 @@
> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/misc/vm-wdt.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: VM watchdog
> +
> +description: |
> +  This binding describes a CPU stall detector mechanism for virtual cpus.
> +
> +maintainers:
> +  - Sebastian Ene <sebastianene@...gle.com>
> +
> +properties:
> +  compatible:
> +    enum:
> +      - qemu,vm-watchdog
> +  clock:

'clocks' is already a defined property and 'clock' is too close. It's 
also ambiguous what it is. 'clock-frequency' instead perhaps.

> +    $ref: /schemas/types.yaml#/definitions/uint32
> +    description: |
> +      The watchdog internal clock measure in Hz used to decrement the
> +      watchdog counter register on each tick.
> +      Defaults to 10 if unset.
> +  timeout-sec:
> +    $ref: /schemas/types.yaml#/definitions/uint32
> +    description: |
> +      The watchdog expiration timeout measured in seconds.
> +      Defaults to 8 if unset.
> +
> +required:
> +  - compatible
> +
> +additionalProperties: false
> +
> +examples:
> +  - |
> +    watchdog {
> +      compatible = "qemu,vm-watchdog";
> +      clock = <10>;
> +      timeout-sec = <8>;

How does one access this 'hardware'?

Why does this need to be in DT?

We have DT because h/w designers are incapable of making h/w 
discoverable. Why repeat that problem with s/w interfaces?

Rob