linux-kernel - Re: [PATCH] arm64: dts: allwinner: Add cache information to the SoC dtsi for A64

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Message-ID: <20240429113321.1f4da653@donnerap.manchester.arm.com>
Date: Mon, 29 Apr 2024 11:33:21 +0100
From: Andre Przywara <andre.przywara@....com>
To: Dragan Simic <dsimic@...jaro.org>
Cc: linux-sunxi@...ts.linux.dev, wens@...e.org, jernej.skrabec@...il.com,
 samuel@...lland.org, linux-arm-kernel@...ts.infradead.org,
 devicetree@...r.kernel.org, robh@...nel.org, krzk+dt@...nel.org,
 conor+dt@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arm64: dts: allwinner: Add cache information to the SoC
 dtsi for A64

On Sun, 28 Apr 2024 13:40:35 +0200
Dragan Simic <dsimic@...jaro.org> wrote:

Hi,

thanks for taking care of this!

> Add missing cache information to the Allwinner A64 SoC dtsi, to allow
> the userspace, which includes lscpu(1) that uses the virtual files provided
> by the kernel under the /sys/devices/system/cpu directory, to display the
> proper A64 cache information.
> 
> While there, use a more self-descriptive label for the L2 cache node, which
> also makes it more consistent with other SoC dtsi files.
> 
> The cache parameters for the A64 dtsi were obtained and partially derived
> by hand from the cache size and layout specifications found in the following
> datasheets and technical reference manuals:
> 
>   - Allwinner A64 datasheet, version 1.1
>   - ARM Cortex-A53 revision r0p3 TRM, version E
> 
> For future reference, here's a brief summary of the documentation:
> 
>   - All caches employ the 64-byte cache line length
>   - Each Cortex-A53 core has 32 KB of L1 2-way, set-associative instruction
>     cache and 32 KB of L1 4-way, set-associative data cache
>   - The entire SoC has 512 KB of unified L2 16-way, set-associative cache

So that looks correct when checking the manuals, and the per-CPU
entries below match both between themselves and with that description
above.
However I have some level of distrust towards the Allwinner manuals,
regarding the cache sizes (which are chosen by Allwinner).
So while I haven't measured this myself, nor checked the cache type
registers, tinymembench's memory latency test supports those sizes are
correct:
https://github.com/ssvb/tinymembench/wiki/PINE64-(Allwinner-A64)

> Signed-off-by: Dragan Simic <dsimic@...jaro.org>

Reviewed-by: Andre Przywara <andre.przywara@....com>

Cheers,
Andre

> ---
>  arch/arm64/boot/dts/allwinner/sun50i-a64.dtsi | 37 ++++++++++++++++---
>  1 file changed, 32 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/arm64/boot/dts/allwinner/sun50i-a64.dtsi b/arch/arm64/boot/dts/allwinner/sun50i-a64.dtsi
> index 57ac18738c99..86074d03afa9 100644
> --- a/arch/arm64/boot/dts/allwinner/sun50i-a64.dtsi
> +++ b/arch/arm64/boot/dts/allwinner/sun50i-a64.dtsi
> @@ -51,49 +51,76 @@ cpu0: cpu@0 {
>  			device_type = "cpu";
>  			reg = <0>;
>  			enable-method = "psci";
> -			next-level-cache = <&L2>;
>  			clocks = <&ccu CLK_CPUX>;
>  			clock-names = "cpu";
>  			#cooling-cells = <2>;
> +			i-cache-size = <0x8000>;
> +			i-cache-line-size = <64>;
> +			i-cache-sets = <256>;
> +			d-cache-size = <0x8000>;
> +			d-cache-line-size = <64>;
> +			d-cache-sets = <128>;
> +			next-level-cache = <&l2_cache>;
>  		};
>  
>  		cpu1: cpu@1 {
>  			compatible = "arm,cortex-a53";
>  			device_type = "cpu";
>  			reg = <1>;
>  			enable-method = "psci";
> -			next-level-cache = <&L2>;
>  			clocks = <&ccu CLK_CPUX>;
>  			clock-names = "cpu";
>  			#cooling-cells = <2>;
> +			i-cache-size = <0x8000>;
> +			i-cache-line-size = <64>;
> +			i-cache-sets = <256>;
> +			d-cache-size = <0x8000>;
> +			d-cache-line-size = <64>;
> +			d-cache-sets = <128>;
> +			next-level-cache = <&l2_cache>;
>  		};
>  
>  		cpu2: cpu@2 {
>  			compatible = "arm,cortex-a53";
>  			device_type = "cpu";
>  			reg = <2>;
>  			enable-method = "psci";
> -			next-level-cache = <&L2>;
>  			clocks = <&ccu CLK_CPUX>;
>  			clock-names = "cpu";
>  			#cooling-cells = <2>;
> +			i-cache-size = <0x8000>;
> +			i-cache-line-size = <64>;
> +			i-cache-sets = <256>;
> +			d-cache-size = <0x8000>;
> +			d-cache-line-size = <64>;
> +			d-cache-sets = <128>;
> +			next-level-cache = <&l2_cache>;
>  		};
>  
>  		cpu3: cpu@3 {
>  			compatible = "arm,cortex-a53";
>  			device_type = "cpu";
>  			reg = <3>;
>  			enable-method = "psci";
> -			next-level-cache = <&L2>;
>  			clocks = <&ccu CLK_CPUX>;
>  			clock-names = "cpu";
>  			#cooling-cells = <2>;
> +			i-cache-size = <0x8000>;
> +			i-cache-line-size = <64>;
> +			i-cache-sets = <256>;
> +			d-cache-size = <0x8000>;
> +			d-cache-line-size = <64>;
> +			d-cache-sets = <128>;
> +			next-level-cache = <&l2_cache>;
>  		};
>  
> -		L2: l2-cache {
> +		l2_cache: l2-cache {
>  			compatible = "cache";
>  			cache-level = <2>;
>  			cache-unified;
> +			cache-size = <0x80000>;
> +			cache-line-size = <64>;
> +			cache-sets = <512>;
>  		};
>  	};
>  
>