linux-kernel - Re: [PATCH] ARM: dts: exynos4212-tab3: limit usable memory range

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Date: Sun, 18 Feb 2024 11:24:49 +0100
From: Henrik Grimler <henrik@...mler.se>
To: Artur Weber <aweber.kernel@...il.com>
Cc: Rob Herring <robh+dt@...nel.org>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Alim Akhtar <alim.akhtar@...sung.com>, devicetree@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	linux-samsung-soc@...r.kernel.org, linux-kernel@...r.kernel.org,
	~postmarketos/upstreaming@...ts.sr.ht
Subject: Re: [PATCH] ARM: dts: exynos4212-tab3: limit usable memory range

Hi Artur,

On Sat, Feb 17, 2024 at 08:02:47PM +0100, Artur Weber wrote:
> The stock bootloader on the Samsung Galaxy Tab 3 8.0 provides an
> incorrect available memory range over ATAG_MEM. Limit the usable
> memory in the DTS to prevent it from doing so, without having to
> disable ATAG support.
> 
> Signed-off-by: Artur Weber <aweber.kernel@...il.com>
> ---
>  arch/arm/boot/dts/samsung/exynos4212-tab3.dtsi | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/arch/arm/boot/dts/samsung/exynos4212-tab3.dtsi b/arch/arm/boot/dts/samsung/exynos4212-tab3.dtsi
> index e5254e32aa8f..9bc05961577d 100644
> --- a/arch/arm/boot/dts/samsung/exynos4212-tab3.dtsi
> +++ b/arch/arm/boot/dts/samsung/exynos4212-tab3.dtsi
> @@ -45,6 +45,12 @@ chosen {
>  		/* Default S-BOOT bootloader loads initramfs here */
>  		linux,initrd-start = <0x42000000>;
>  		linux,initrd-end = <0x42800000>;
> +
> +		/*
> +		 * Stock bootloader provides incorrect memory size in ATAG_MEM;
> +		 * override it here
> +		 */
> +		linux,usable-memory-range = <0x40000000 0x3fc00000>;

Maybe it would make sense to set the memory reg to
<0x40000000 0x60000000> (1.5 GiB) and move the comment about last
512(/516) MiB being weird/broken here instead.  It looks a bit weird
that the memory range and usable-memory-range are identical, and device tree
should describe hardware, which technically has 1.5 GiB RAM.

>From a functional point of view it does not really matter, so in any case:
Reviewed-by: Henrik Grimler <henrik@...mler.se>

>  	};
>  
>  	firmware@...f000 {
> 
> ---
> base-commit: 0f1dd5e91e2ba3990143645faff2bcce2d99778e
> change-id: 20240217-tab3-limit-usable-memory-range-1d1ffa8dc44d
> 
> Best regards,
> -- 
> Artur Weber <aweber.kernel@...il.com>
>