linux-kernel - Re: [PATCH RFC v4 05/15] spi: dt-bindings: add PWM SPI offload trigger

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Message-ID: <20241026161837.30a56ae1@jic23-huawei>
Date: Sat, 26 Oct 2024 16:18:37 +0100
From: Jonathan Cameron <jic23@...nel.org>
To: David Lechner <dlechner@...libre.com>
Cc: Mark Brown <broonie@...nel.org>, Rob Herring <robh@...nel.org>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
 <conor+dt@...nel.org>, Nuno Sá <nuno.sa@...log.com>, Uwe
 Kleine-König <ukleinek@...nel.org>, Michael Hennerich
 <Michael.Hennerich@...log.com>, Lars-Peter Clausen <lars@...afoo.de>, David
 Jander <david@...tonic.nl>, Martin Sperl <kernel@...tin.sperl.org>,
 linux-spi@...r.kernel.org, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-iio@...r.kernel.org,
 linux-pwm@...r.kernel.org
Subject: Re: [PATCH RFC v4 05/15] spi: dt-bindings: add PWM SPI offload
 trigger

On Wed, 23 Oct 2024 15:59:12 -0500
David Lechner <dlechner@...libre.com> wrote:

> Add a new binding for using a PWM signal as a trigger for SPI offloads.

I don't have a better suggestion for this, but it does smell rather like
other bridge binding (iio-hwmon for example) where we have had push back on
representing something that doesn't really exist but is just a way to
tie two bits of hardware together. Those kind of exist because we snuck
them in a long time back when no one was paying attention.

So this one may need more explanation and justification and I'd definitely
like some DT maintainer review on this at a fairly early stage!
(might have happened in earlier reviews but it has been a while so I've
forgotten if it did)

Jonathan


> 
> Signed-off-by: David Lechner <dlechner@...libre.com>
> ---
> 
> v4 changes: new patch in v4
> ---
>  .../devicetree/bindings/spi/trigger-pwm.yaml       | 39 ++++++++++++++++++++++
>  1 file changed, 39 insertions(+)
> 
> diff --git a/Documentation/devicetree/bindings/spi/trigger-pwm.yaml b/Documentation/devicetree/bindings/spi/trigger-pwm.yaml
> new file mode 100644
> index 000000000000..987638aa4732
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/spi/trigger-pwm.yaml
> @@ -0,0 +1,39 @@
> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/spi/trigger-pwm.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: Generic SPI offload trigger using PWM
> +
> +description: Remaps a PWM channel as a trigger source.
> +
> +maintainers:
> +  - David Lechner <dlechner@...libre.com>
> +
> +$ref: /schemas/spi/trigger-source.yaml#
> +
> +properties:
> +  compatible:
> +    const: trigger-pwm
> +
> +  '#trigger-source-cells':
> +    const: 0
> +
> +  pwms:
> +    maxItems: 1
> +
> +required:
> +  - compatible
> +  - '#trigger-source-cells'
> +  - pwms
> +
> +additionalProperties: false
> +
> +examples:
> +  - |
> +    trigger {
> +        compatible = "trigger-pwm";
> +        #trigger-source-cells = <0>;
> +        pwms = <&pwm 0 1000000 0>;
> +    };
>