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Date: Wed, 10 Jan 2024 17:14:56 -0600
From: Rob Herring <robh@...nel.org>
To: David Lechner <dlechner@...libre.com>
Cc: Mark Brown <broonie@...nel.org>, Jonathan Cameron <jic23@...nel.org>, Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>, Conor Dooley <conor+dt@...nel.org>, Michael Hennerich <michael.hennerich@...log.com>, Nuno Sá <nuno.sa@...log.com>, Frank Rowand <frowand.list@...il.com>, Thierry Reding <thierry.reding@...il.com>, Uwe Kleine-König <u.kleine-koenig@...gutronix.de>, Jonathan Corbet <corbet@....net>, linux-spi@...r.kernel.org, linux-iio@...r.kernel.org, devicetree@...r.kernel.org, linux-doc@...r.kernel.org, linux-pwm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 04/13] spi: dt-bindings: adi,axi-spi-engine: add offload
bindings
On Wed, Jan 10, 2024 at 01:49:45PM -0600, David Lechner wrote:
> The ADI AXI SPI Engine driver supports offloading SPI transfers to
> hardware. This is essentially a feature that allows recording an
> arbitrary sequence of SPI transfers and then playing them back with
> no CPU intervention via a hardware trigger.
>
> This adds the bindings for this feature. Each SPI Engine instance
> can have from 0 to 32 offload instances. Each offload instance has a
> trigger input and a data stream output. As an example, this could be
> used with an ADC SPI peripheral. In this case the trigger is connected
> to a PWM/clock to determine the sampling rate for the ADC and the output
> stream is connected to a DMA channel to pipe the sample data to memory.
>
> SPI peripherals act as consumers of the offload instances. Typically,
> one SPI peripheral will be connected to one offload instance. But to
> make the bindings future-proof, the property is an array.
Is there some sort of arbitration between multiple offload engines on
the same chip select? If not, I don't see how it would work.
I think this whole thing could be simplified down to just 3
SPI controller properties: pwms, dmas, and adi,offload-cs-map. Each
property is has entries equal the number of offload engines. The last
one maps an offload engine to a SPI chip-select.
>
> Signed-off-by: David Lechner <dlechner@...libre.com>
> ---
> .../spi/adi,axi-spi-engine-peripheral-props.yaml | 24 +++++++++++
> .../bindings/spi/adi,axi-spi-engine.yaml | 49 +++++++++++++++++++++-
> .../bindings/spi/spi-peripheral-props.yaml | 1 +
> 3 files changed, 73 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/devicetree/bindings/spi/adi,axi-spi-engine-peripheral-props.yaml b/Documentation/devicetree/bindings/spi/adi,axi-spi-engine-peripheral-props.yaml
> new file mode 100644
> index 000000000000..19b685fc3b39
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/spi/adi,axi-spi-engine-peripheral-props.yaml
> @@ -0,0 +1,24 @@
> +# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/spi/adi,axi-spi-engine-peripheral-props.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: Peripheral properties for Analog Devices AXI SPI Engine Controller
> +
> +maintainers:
> + - Michael Hennerich <Michael.Hennerich@...log.com>
> + - Nuno Sá <nuno.sa@...log.com>
> +
> +properties:
> + adi,offloads:
> + description:
> + List of AXI SPI Engine offload instances assigned to this peripheral.
> + $ref: /schemas/types.yaml#/definitions/uint32-array
> + maxItems: 32
> + items:
> + items:
> + - minimum: 0
> + maximum: 31
This defines a matrix. You want:
minItems: 1
maxItems: 32
items:
maximum: 31
(0 is already the min).
> +
> +additionalProperties: true
> diff --git a/Documentation/devicetree/bindings/spi/adi,axi-spi-engine.yaml b/Documentation/devicetree/bindings/spi/adi,axi-spi-engine.yaml
> index d48faa42d025..69f3261bab47 100644
> --- a/Documentation/devicetree/bindings/spi/adi,axi-spi-engine.yaml
> +++ b/Documentation/devicetree/bindings/spi/adi,axi-spi-engine.yaml
> @@ -21,6 +21,23 @@ maintainers:
> allOf:
> - $ref: /schemas/spi/spi-controller.yaml#
>
> +$defs:
> + offload:
> + description:
> + Describes the connections of the trigger input and the data output stream
> + of one or more offload instances.
> +
> + properties:
> + reg:
> + description:
> + Index of the offload instance.
> + items:
> + - minimum: 0
> + maximum: 31
> +
> + required:
> + - reg
> +
> properties:
> compatible:
> const: adi,axi-spi-engine-1.00.a
> @@ -41,6 +58,22 @@ properties:
> - const: s_axi_aclk
> - const: spi_clk
>
> + offloads:
> + type: object
> + description: Zero or more offloads supported by the controller.
> +
> + properties:
> + "#address-cells":
> + const: 1
> +
> + "#size-cells":
> + const: 0
> +
> + patternProperties:
> + "^offload@[0-8a-f]+$":
> + type: object
> + $ref: '#/$defs/offload'
> +
> required:
> - compatible
> - reg
> @@ -62,5 +95,19 @@ examples:
> #address-cells = <1>;
> #size-cells = <0>;
>
> - /* SPI devices */
> + offloads {
> + #address-cells = <1>;
> + #size-cells = <0>;
> +
> + offload@0 {
> + compatible = "adi,example-offload";
No fake examples please. This should give you a warning.
> + reg = <0>;
> + };
> + };
> +
> + adc@0 {
> + compatible = "adi,example-adc";
> + reg = <0>;
> + adi,offloads = <0>;
> + };
> };
> diff --git a/Documentation/devicetree/bindings/spi/spi-peripheral-props.yaml b/Documentation/devicetree/bindings/spi/spi-peripheral-props.yaml
> index 1c8e71c18234..7beb5a3798a5 100644
> --- a/Documentation/devicetree/bindings/spi/spi-peripheral-props.yaml
> +++ b/Documentation/devicetree/bindings/spi/spi-peripheral-props.yaml
> @@ -132,6 +132,7 @@ properties:
>
> # The controller specific properties go here.
> allOf:
> + - $ref: adi,axi-spi-engine-peripheral-props.yaml#
> - $ref: arm,pl022-peripheral-props.yaml#
> - $ref: cdns,qspi-nor-peripheral-props.yaml#
> - $ref: samsung,spi-peripheral-props.yaml#
>
> --
> 2.43.0
>
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