linux-kernel - Re: [RFC 1/3] dt-bindings: dma: Add documentation for DMA domains

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Date:   Sun, 8 Sep 2019 17:36:42 +0530
From:   Vinod Koul <vkoul@...nel.org>
To:     Peter Ujfalusi <peter.ujfalusi@...com>
Cc:     robh+dt@...nel.org, dmaengine@...r.kernel.org,
        linux-kernel@...r.kernel.org, dan.j.williams@...el.com,
        devicetree@...r.kernel.org
Subject: Re: [RFC 1/3] dt-bindings: dma: Add documentation for DMA domains

On 06-09-19, 17:18, Peter Ujfalusi wrote:
> On systems where multiple DMA controllers available, none Slave (for example

On systems with multiple DMA controllers, non Slave...

> memcpy operation) users can not be described in DT as there is no device
> involved from the DMA controller's point of view, DMA binding is not usable.
> However in these systems still a peripheral might need to be serviced by or
> it is better to serviced by specific DMA controller.
> When a memcpy is used to/from a memory mapped region for example a DMA in the
> same domain can perform better.
> For generic software modules doing mem 2 mem operations it also matter that
> they will get a channel from a controller which is faster in DDR to DDR mode
> rather then from the first controller happen to be loaded.
> 
> This property is inherited, so it may be specified in a device node or in any
> of its parent nodes.
> 
> Signed-off-by: Peter Ujfalusi <peter.ujfalusi@...com>
> ---
>  .../devicetree/bindings/dma/dma-domain.yaml   | 59 +++++++++++++++++++
>  1 file changed, 59 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/dma/dma-domain.yaml
> 
> diff --git a/Documentation/devicetree/bindings/dma/dma-domain.yaml b/Documentation/devicetree/bindings/dma/dma-domain.yaml
> new file mode 100644
> index 000000000000..c2f182f30081
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/dma/dma-domain.yaml
> @@ -0,0 +1,59 @@
> +# SPDX-License-Identifier: GPL-2.0
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/dma/dma-controller.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: DMA Domain Controller Definition
> +
> +maintainers:
> +  - Vinod Koul <vkoul@...nel.org>
> +
> +allOf:
> +  - $ref: "dma-controller.yaml#"
> +
> +description:
> +  On systems where multiple DMA controllers available, none Slave (for example
> +  memcpy operation) users can not be described in DT as there is no device
> +  involved from the DMA controller's point of view, DMA binding is not usable.
> +  However in these systems still a peripheral might need to be serviced by or
> +  it is better to serviced by specific DMA controller.
> +  When a memcpy is used to/from a memory mapped region for example a DMA in the
> +  same domain can perform better.
> +  For generic software modules doing mem 2 mem operations it also matter that
> +  they will get a channel from a controller which is faster in DDR to DDR mode
> +  rather then from the first controller happen to be loaded.
> +
> +  This property is inherited, so it may be specified in a device node or in any
> +  of its parent nodes.
> +
> +properties:
> +  $dma-domain-controller:
> +    $ref: /schemas/types.yaml#definitions/phandle
> +    description:
> +      phande to the DMA controller node which should be used for the device or
> +      domain.
> +
> +examples:
> +  - |
> +    / {
> +        model = "Texas Instruments K3 AM654 SoC";
> +        compatible = "ti,am654";
> +        interrupt-parent = <&gic500>;
> +        /* For modules without device, DDR to DDR is faster on main UDMAP */
> +        dma-domain-controller = <&main_udmap>;
> +        #address-cells = <2>;
> +        #size-cells = <2>;
> +        ...
> +    };
> +
> +    &cbass_main {
> +        /* For modules within MAIN domain, use main UDMAP */
> +        dma-domain-controller = <&main_udmap>;
> +    };
> +
> +    &cbass_mcu {
> +        /* For modules within MCU domain, use mcu UDMAP */
> +        dma-domain-controller = <&mcu_udmap>;

perhaps add the example of main_udmap and mcu_udmap as well

> +    };
> +...
> -- 
> Peter
> 
> Texas Instruments Finland Oy, Porkkalankatu 22, 00180 Helsinki.
> Y-tunnus/Business ID: 0615521-4. Kotipaikka/Domicile: Helsinki

-- 
~Vinod