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

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Date: Mon, 19 Feb 2024 20:49:46 +0100
From: Artur Weber <aweber.kernel@...il.com>
To: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
 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>
Cc: 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

On 19.02.2024 08:44, Krzysztof Kozlowski wrote:
> On 17/02/2024 20:02, 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>;
> 
> Applied and dropped:
>   chosen: linux,usable-memory-range:0: [4611686019496935424] is too short

This seems to be a binding issue; the DT schema expects a 64-bit memory 
address and size, and doesn't allow a 32-bit range. I've tested the DTS 
on my device and this property seems to be handled fine, so I think this 
should allow 32-bit values as well.

I've opened a PR[1] against devicetree-org/dt-schema (where the schema 
for the chosen node is stored) to try and fix this. If my approach is 
incorrect, feel free to comment there as well.

Best regards
Artur

[1] https://github.com/devicetree-org/dt-schema/pull/128

> 
> Does not look you tested the bindings.
> 
> Please observe that we have dedicated subsystem profile since a release:
> https://www.kernel.org/doc/html/latest/process/maintainers.html#arm-samsung-s3c-s5p-and-exynos-arm-architectures
> 
> Best regards,
> Krzysztof
>