linux-kernel - Re: [PATCH] arm64: dts: qcom: add missing cache node for cpu1

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Message-ID: <f105e797-4b78-470f-95b5-6d6b025dc576@linaro.org>
Date: Fri, 10 Jan 2025 10:49:50 +0100
From: Neil Armstrong <neil.armstrong@...aro.org>
To: Konrad Dybcio <konrad.dybcio@....qualcomm.com>,
 Bjorn Andersson <andersson@...nel.org>,
 Konrad Dybcio <konradybcio@...nel.org>, Rob Herring <robh@...nel.org>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>
Cc: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
 linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arm64: dts: qcom: add missing cache node for cpu1

On 10/01/2025 10:44, Neil Armstrong wrote:
> On 09/01/2025 19:30, Konrad Dybcio wrote:
>> On 9.01.2025 4:24 PM, Neil Armstrong wrote:
>>> Add the missing l2-cache node for the cpu1
>>>
>>> Fixes: 20eb2057b3e4 ("arm64: dts: qcom: sm8650: change labels to lower-case")
>>> Fixes: d2350377997f ("arm64: dts: qcom: add initial SM8650 dtsi")
>>> Signed-off-by: Neil Armstrong <neil.armstrong@...aro.org>
>>> ---
>>
>> subject: missing `sm8650:`
> 
> Damn
> 
>>
>>>   arch/arm64/boot/dts/qcom/sm8650.dtsi | 7 +++++++
>>>   1 file changed, 7 insertions(+)
>>>
>>> diff --git a/arch/arm64/boot/dts/qcom/sm8650.dtsi b/arch/arm64/boot/dts/qcom/sm8650.dtsi
>>> index 86684cb9a9325618ddb74458621cf4bbdc1cc0d1..832f3a2c400e8348847bc24b27397e2a0dc08db8 100644
>>> --- a/arch/arm64/boot/dts/qcom/sm8650.dtsi
>>> +++ b/arch/arm64/boot/dts/qcom/sm8650.dtsi
>>> @@ -119,6 +119,13 @@ cpu1: cpu@100 {
>>>               qcom,freq-domain = <&cpufreq_hw 0>;
>>>               #cooling-cells = <2>;
>>> +
>>> +            l2_100: l2-cache {
>>> +                compatible = "cache";
>>> +                cache-level = <2>;
>>> +                cache-unified;
>>> +                next-level-cache = <&l3_0>;
>>> +            };
>>>           };
>>
>> You likely wanted to hook up this new node to CPU1 as well.
>>
>> Reading some Arm docs [1], it seems like with A520 specifically, both shared
>> and unique cache slices are permitted, depending on whether they're
>> implemented as single- or dual-core complexes (not to be confused with
>> multi-threading)
>>
>> [2] suggests CA720s always have their own cache pools
>>
>> In 8650's case, the slowest cluster has a shared L2 cache, whereas cores 2-7
>> have their own pools, so this patch is incorrect.
> 
> Damn you're right, so the cpu1 cache should be linked to the cpu0 cache somehow

Well, stupid me, it's already done... sorry for the noise and thx for your review

Neil

> 
> Thanks,
> Neil
> 
>>
>> Konrad
>>
>> [1] https://developer.arm.com/documentation/102517/0004/The-Cortex-A520--core/Cortex-A520--core-configuration-options
>> [2] https://developer.arm.com/documentation/102530/0001/L2-memory-system
>