linux-kernel - Re: [PATCH v2 2/3] arm64: tegra: Add GPCDMA support for Tegra I2C

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Message-ID: <Y0AnpYeECoyQchmY@orome>
Date:   Fri, 7 Oct 2022 15:20:37 +0200
From:   Thierry Reding <thierry.reding@...il.com>
To:     Akhil R <akhilrajeev@...dia.com>
Cc:     christian.koenig@....com, devicetree@...r.kernel.org,
        digetx@...il.com, jonathanh@...dia.com, ldewangan@...dia.com,
        linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-tegra@...r.kernel.org, robh+dt@...nel.org,
        sumit.semwal@...aro.org, wsa@...nel.org
Subject: Re: [PATCH v2 2/3] arm64: tegra: Add GPCDMA support for Tegra I2C

On Tue, Sep 06, 2022 at 08:17:15PM +0530, Akhil R wrote:
> Add dma properties to support GPCDMA for I2C in Tegra 186 and later
> chips
> 
> Signed-off-by: Akhil R <akhilrajeev@...dia.com>
> ---
>  arch/arm64/boot/dts/nvidia/tegra186.dtsi | 32 ++++++++++++++++++++++++
>  arch/arm64/boot/dts/nvidia/tegra194.dtsi | 32 ++++++++++++++++++++++++
>  arch/arm64/boot/dts/nvidia/tegra234.dtsi | 32 ++++++++++++++++++++++++
>  3 files changed, 96 insertions(+)
> 
> diff --git a/arch/arm64/boot/dts/nvidia/tegra186.dtsi b/arch/arm64/boot/dts/nvidia/tegra186.dtsi
> index 59a10fb184f8..3580fbf99091 100644
> --- a/arch/arm64/boot/dts/nvidia/tegra186.dtsi
> +++ b/arch/arm64/boot/dts/nvidia/tegra186.dtsi
> @@ -672,6 +672,10 @@
>  		clock-names = "div-clk";
>  		resets = <&bpmp TEGRA186_RESET_I2C1>;
>  		reset-names = "i2c";
> +		iommus = <&smmu TEGRA186_SID_GPCDMA_0>;
> +		dma-coherent;

I wonder: why do we need the iommus and dma-coherent properties here?
The I2C controllers are not directly accessing memory, instead it's the
GPCDMA via the dmas/dma-names properties. The GPCDMA already has these
properties set, so they seem to be useless here.

I'm asking because they cause a lot of warnings from the DT validators,
so we either need to remove them (if they are not necessary) or add the
DT binding documentation for them.

Thierry

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