linux-kernel - Re: [PATCH 1/2] arm64: dts: qcom: sm8650: switch to interrupt-cells 4 to add PPI partitions

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Message-ID: <5b782e14-5262-49f9-938b-b8c9b8935f6a@linaro.org>
Date: Mon, 10 Feb 2025 10:27:19 +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: linux-arm-msm@...r.kernel.org, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] arm64: dts: qcom: sm8650: switch to interrupt-cells 4
 to add PPI partitions

On 09/02/2025 15:45, Neil Armstrong wrote:
> On 07/02/2025 21:23, Konrad Dybcio wrote:
>> On 7.02.2025 11:31 AM, Neil Armstrong wrote:
>>> The ARM PMUs shares the same per-cpu (PPI) interrupt, so we need to switch
>>> to interrupt-cells = <4> in the GIC node to allow adding an interrupt
>>> partition map phandle as the 4th cell value for GIC_PPI interrupts.
>>>
>>> Signed-off-by: Neil Armstrong <neil.armstrong@...aro.org>
>>> ---
>>
>> If I'm reading the core right, we can leave the fourth cell
>> uninitialized where it makes no sense
> 
> It's not what dtbs_check thinks !

And if you don't specify the 4th cell, dtc is not happy at all:

arch/arm64/boot/dts/qcom/sm8650.dtsi:5302.4-27: Warning (interrupts_property): /soc@...imer@...20000/frame@...2d000:#interrupt-cells: size is (12), expected multiple of 16
arch/arm64/boot/dts/qcom/sm8650.dtsi:5302.4-27: Warning (interrupts_property): /soc@...sc@...00000:#interrupt-cells: size is (36), expected multiple of 16
arch/arm64/boot/dts/qcom/sm8650.dtsi:5302.4-27: Warning (interrupts_property): /soc@...mc@...4000:#interrupt-cells: size is (24), expected multiple of 16
...
for a good reason, if you specify 4 cells and you specify multiple interrupts the
DT code will split the interrupts entry by interrupts-cells + 1.

Remember we pass the DT in the DTB format without all the verbosity of DTS,
the properly is only a bunch of u32 blobs we can extract with the help
of the -cells properties of the providers.

Neil

> 
>>
>> Konrad
>