linux-kernel - Re: [PATCH v1] arm64: dts: imx8qm: added System MMU

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Message-ID: <d10b6230-6a7d-05c9-47ec-6defe840d827@arm.com>
Date:   Wed, 14 Jul 2021 15:37:58 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     Oliver Graute <oliver.graute@...oconnector.com>,
        shawnguo@...nel.org
Cc:     devicetree@...r.kernel.org, aisheng.dong@....com,
        fabio.estevam@....com, Rob Herring <robh+dt@...nel.org>,
        Sascha Hauer <kernel@...gutronix.de>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Fabio Estevam <festevam@...il.com>,
        NXP Linux Team <linux-imx@....com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] arm64: dts: imx8qm: added System MMU

On 2021-07-14 13:09, Oliver Graute wrote:
> added node for System MMU

Note that it's a bit of a dangerous game to enable an SMMU without the 
complete Stream ID topology for *all* its upstream devices also 
described, since CONFIG_ARM_SMMU_DISABLE_BYPASS_BY_DEFAULT will ruin 
peoples' day. It might be more polite to add it in a disabled state 
until every "iommus" property has been filled in, so that people who do 
want to play with it for specific devices in the meantime can easily 
just flip the status (while taking the necessary precautions), but 
people who don't care won't be inadvertently affected regardless of 
their kernel config. I'm assuming an SMMU with 32 contexts has more than 
a single USB controller behind it...

Robin.

> Cc: Rob Herring <robh+dt@...nel.org>
> Cc: Sascha Hauer <kernel@...gutronix.de>
> Cc: Fabio Estevam <fabio.estevam@....com>
> Cc: Dong Aisheng <aisheng.dong@....com>
> 
> Signed-off-by: Oliver Graute <oliver.graute@...oconnector.com>
> ---
>   arch/arm64/boot/dts/freescale/imx8qm.dtsi | 17 +++++++++++++++++
>   1 file changed, 17 insertions(+)
> 
> diff --git a/arch/arm64/boot/dts/freescale/imx8qm.dtsi b/arch/arm64/boot/dts/freescale/imx8qm.dtsi
> index 7efc0add74ea..fa827ed04e09 100644
> --- a/arch/arm64/boot/dts/freescale/imx8qm.dtsi
> +++ b/arch/arm64/boot/dts/freescale/imx8qm.dtsi
> @@ -140,6 +140,23 @@
>   		method = "smc";
>   	};
>   
> +	smmu: iommu@...00000 {
> +		compatible = "arm,mmu-500";
> +		interrupt-parent = <&gic>;
> +		reg = <0 0x51400000 0 0x40000>;
> +		#global-interrupts = <1>;
> +		#iommu-cells = <2>;
> +		interrupts = <0 32 4>,
> +			     <0 32 4>, <0 32 4>, <0 32 4>, <0 32 4>,
> +			     <0 32 4>, <0 32 4>, <0 32 4>, <0 32 4>,
> +			     <0 32 4>, <0 32 4>, <0 32 4>, <0 32 4>,
> +			     <0 32 4>, <0 32 4>, <0 32 4>, <0 32 4>,
> +			     <0 32 4>, <0 32 4>, <0 32 4>, <0 32 4>,
> +			     <0 32 4>, <0 32 4>, <0 32 4>, <0 32 4>,
> +			     <0 32 4>, <0 32 4>, <0 32 4>, <0 32 4>,
> +			     <0 32 4>, <0 32 4>, <0 32 4>, <0 32 4>;
> +	};
> +
>   	timer {
>   		compatible = "arm,armv8-timer";
>   		interrupts = <GIC_PPI 13 IRQ_TYPE_LEVEL_LOW>, /* Physical Secure */
>