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From:   Arnd Bergmann <arnd@arndb.de>
Date:   Wed, 30 Jan 2019 17:51:46 +0100
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Subject: Re: [PATCH 1/3] dt-bindings: dmaengine: Add one new cell to present
 hardware slave id
To:     Baolin Wang <baolin.wang@linaro.org>
Cc:     Vinod Koul <vkoul@kernel.org>, Rob Herring <robh+dt@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Olof Johansson <olof@lixom.net>,
        Orson Zhai <orsonzhai@gmail.com>,
        Lyra Zhang <zhang.lyra@gmail.com>,
        Dan Williams <dan.j.williams@intel.com>,
        DTML <devicetree@vger.kernel.org>, arm-soc <arm@kernel.org>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        dmaengine@vger.kernel.org, eric.long@unisoc.com,
        Mark Brown <broonie@kernel.org>
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On Tue, Jan 22, 2019 at 2:21 PM Baolin Wang <baolin.wang@linaro.org> wrote:
>
> The DMA engine clients can trigger DMA engine automatically by setting
> the corresponding hardware slave id for the DMA engine. Thus add one
> cell to present the hardware slave id for DMA clients.
>
> Signed-off-by: Baolin Wang <baolin.wang@linaro.org>
> ---
>  Documentation/devicetree/bindings/dma/sprd-dma.txt |   12 +++++++-----
>  1 file changed, 7 insertions(+), 5 deletions(-)
>
> diff --git a/Documentation/devicetree/bindings/dma/sprd-dma.txt b/Documentation/devicetree/bindings/dma/sprd-dma.txt
> index 7a10fea..7812cf0 100644
> --- a/Documentation/devicetree/bindings/dma/sprd-dma.txt
> +++ b/Documentation/devicetree/bindings/dma/sprd-dma.txt
> @@ -6,8 +6,8 @@ Required properties:
>  - compatible: Should be "sprd,sc9860-dma".
>  - reg: Should contain DMA registers location and length.
>  - interrupts: Should contain one interrupt shared by all channel.
> -- #dma-cells: must be <1>. Used to represent the number of integer
> -       cells in the dmas property of client device.
> +- #dma-cells: must be <2>. Used to represent the channel id and slave id
> +       of integer cells in the dmas property of client device.
>  - #dma-channels : Number of DMA channels supported. Should be 32.
>  - clock-names: Should contain the clock of the DMA controller.
>  - clocks: Should contain a clock specifier for each entry in clock-names.
> @@ -28,14 +28,16 @@ apdma: dma-controller@20100000 {
>
>  Client:
>  DMA clients connected to the Spreadtrum DMA controller must use the format
> -described in the dma.txt file, using a two-cell specifier for each channel.
> -The two cells in order are:
> +described in the dma.txt file, using a three-cell specifier for each channel.
> +The three cells in order are:
>  1. A phandle pointing to the DMA controller.
>  2. The channel id.
> +3. The hardware slave id which is used for clients to trigger DMA engine
> +automatically.

I notice that this is an incompatible binding change. Is that necessary?
If the current code works, I'd suggest allowing both #dma-cells=<2>
and <3>, and then implementing both in the driver.

     Arnd