linux-kernel - Re: [PATCH v2 00/12] coresight: Add CPU cluster funnel/replicator/tmc support

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Message-ID: <e9df1140-989f-46e3-8edc-2013e520bfed@arm.com>
Date: Fri, 19 Dec 2025 10:28:01 +0000
From: Suzuki K Poulose <suzuki.poulose@....com>
To: Sudeep Holla <sudeep.holla@....com>,
 yuanfang zhang <yuanfang.zhang@....qualcomm.com>
Cc: Mike Leach <mike.leach@...aro.org>, James Clark <james.clark@...aro.org>,
 Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
 Conor Dooley <conor+dt@...nel.org>,
 Mathieu Poirier <mathieu.poirier@...aro.org>, Leo Yan <leo.yan@...ux.dev>,
 Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
 Bjorn Andersson <andersson@...nel.org>,
 Konrad Dybcio <konradybcio@...nel.org>, kernel@....qualcomm.com,
 coresight@...ts.linaro.org, linux-arm-kernel@...ts.infradead.org,
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-arm-msm@...r.kernel.org, maulik.shah@....qualcomm.com,
 Jie Gan <jie.gan@....qualcomm.com>
Subject: Re: [PATCH v2 00/12] coresight: Add CPU cluster funnel/replicator/tmc
 support

On 19/12/2025 10:21, Sudeep Holla wrote:
> On Fri, Dec 19, 2025 at 10:13:14AM +0800, yuanfang zhang wrote:
>>
>>
>> On 12/18/2025 7:33 PM, Sudeep Holla wrote:
>>> On Thu, Dec 18, 2025 at 12:09:40AM -0800, Yuanfang Zhang wrote:
>>>> This patch series adds support for CoreSight components local to CPU clusters,
>>>> including funnel, replicator, and TMC, which reside within CPU cluster power
>>>> domains. These components require special handling due to power domain
>>>> constraints.
>>>>
>>>
>>> Could you clarify why PSCI-based power domains associated with clusters in
>>> domain-idle-states cannot address these requirements, given that PSCI CPU-idle
>>> OSI mode was originally intended to support them? My understanding of this
>>> patch series is that OSI mode is unable to do so, which, if accurate, appears
>>> to be a flaw that should be corrected.
>>
>> It is due to the particular characteristics of the CPU cluster power
>> domain.Runtime PM for CPU devices works little different, it is mostly used
>> to manage hierarchicalCPU topology (PSCI OSI mode) to talk with genpd
>> framework to manage the last CPU handling in cluster.
> 
> That is indeed the intended design. Could you clarify which specific
> characteristics differentiate it here?
> 
>> It doesn’t really send IPI to wakeup CPU device (It don’t have
>> .power_on/.power_off) callback implemented which gets invoked from
>> .runtime_resume callback. This behavior is aligned with the upstream Kernel.
>>
> 
> I am quite lost here. Why is it necessary to wake up the CPU? If I understand
> correctly, all of this complexity is meant to ensure that the cluster power
> domain is enabled before any of the funnel registers are accessed. Is that
> correct?
> 
> If so, and if the cluster domains are already defined as the power domains for
> these funnel devices, then they should be requested to power on automatically
> before any register access occurs. Is that not the case?
> 
> What am I missing in this reasoning?

Exactly, this is what I am too. But then you get the "pre-formated 
standard response" without answering our questions.

Suzuki