linux-kernel - Re: [PATCH] DTS: bcm2711: Move emmc2 into its own bus

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Date:   Tue, 3 Mar 2020 10:21:30 -0800
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Nicolas Saenz Julienne <nsaenzjulienne@...e.de>,
        Rob Herring <robh+dt@...nel.org>
Cc:     devicetree@...r.kernel.org, florian.fainelli@...adcom.com,
        phil@...pberrypi.org, linux-kernel@...r.kernel.org,
        bcm-kernel-feedback-list@...adcom.com,
        linux-rpi-kernel@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] DTS: bcm2711: Move emmc2 into its own bus

On 3/3/20 4:08 AM, Nicolas Saenz Julienne wrote:
> Depending on bcm2711's revision its emmc2 controller might have
> different DMA constraints. Raspberry Pi 4's firmware will take care of
> updating those, but only if a certain alias is found in the device tree.
> So, move emmc2 into its own bus, so as not to pollute other devices with
> dma-ranges changes and create the emmc2bus alias.
> 
> Based in Phil ELwell's downstream implementation.
> 
> Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@...e.de>

Nit: the subject should be ARM: dts: bcm2711. Some more comments below.

> ---
>  arch/arm/boot/dts/bcm2711-rpi-4-b.dts |  1 +
>  arch/arm/boot/dts/bcm2711.dtsi        | 19 ++++++++++++++-----
>  2 files changed, 15 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/arm/boot/dts/bcm2711-rpi-4-b.dts b/arch/arm/boot/dts/bcm2711-rpi-4-b.dts
> index 1d4b589fe233..e26ea9006378 100644
> --- a/arch/arm/boot/dts/bcm2711-rpi-4-b.dts
> +++ b/arch/arm/boot/dts/bcm2711-rpi-4-b.dts
> @@ -20,6 +20,7 @@ memory@0 {
>  	};
>  
>  	aliases {
> +		emmc2bus = &emmc2bus;
>  		ethernet0 = &genet;
>  		pcie0 = &pcie0;
>  	};
> diff --git a/arch/arm/boot/dts/bcm2711.dtsi b/arch/arm/boot/dts/bcm2711.dtsi
> index d1e684d0acfd..61ea8b44c51e 100644
> --- a/arch/arm/boot/dts/bcm2711.dtsi
> +++ b/arch/arm/boot/dts/bcm2711.dtsi
> @@ -241,17 +241,26 @@ pwm1: pwm@...0c800 {
>  			status = "disabled";
>  		};
>  
> +		hvs@...00000 {
> +			interrupts = <GIC_SPI 97 IRQ_TYPE_LEVEL_HIGH>;
> +		};
> +	};
> +
> +	emmc2bus: emmc2bus {
> +		compatible = "simple-bus";
> +		#address-cells = <2>;
> +		#size-cells = <1>;
> +
> +		ranges = <0x0 0x7e000000  0x0 0xfe000000  0x01800000>;
> +		dma-ranges = <0x0 0xc0000000  0x0 0x00000000  0x40000000>;

This deserves a comment for two reasons:

- explaining which of these properties is getting patched by the
firmware (and it would be really nice if we had a concept of annotation
attributes for Device Tree such that you could express something like:

	dma-ranges = <> __patchable;

- explaining why this is not collapsed in the soc bus node, because the
dma-ranges constraint can be different based on the Pi4 revision

With that fixed, this looks good to me!

> +
>  		emmc2: emmc2@...40000 {
>  			compatible = "brcm,bcm2711-emmc2";
> -			reg = <0x7e340000 0x100>;
> +			reg = <0x0 0x7e340000 0x100>;
>  			interrupts = <GIC_SPI 126 IRQ_TYPE_LEVEL_HIGH>;
>  			clocks = <&clocks BCM2711_CLOCK_EMMC2>;
>  			status = "disabled";
>  		};
> -
> -		hvs@...00000 {
> -			interrupts = <GIC_SPI 97 IRQ_TYPE_LEVEL_HIGH>;
> -		};
>  	};
>  
>  	arm-pmu {
> 


-- 
Florian