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

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Message-ID: <20251219104241.GB9788@e132581.arm.com>
Date: Fri, 19 Dec 2025 10:42:41 +0000
From: Leo Yan <leo.yan@....com>
To: yuanfang zhang <yuanfang.zhang@....qualcomm.com>
Cc: Suzuki K Poulose <suzuki.poulose@....com>,
	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 Fri, Dec 19, 2025 at 09:50:18AM +0800, yuanfang zhang wrote:

[...]

> 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 hierarchical
> CPU topology (PSCI OSI mode) to talk with genpd framework to manage the last CPU handling in
> cluster.
> 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.

Just for easier understanding, let me give an example:

    funnel0: funnel@...00000 {
        compatible = "arm,coresight-dynamic-funnel", "arm,primecell";
        reg = <0x10000000 0x1000>;

        clocks = <&rpmcc RPM_SMD_QDSS_CLK>, <&rpmcc RPM_SMD_QDSS_A_CLK>;
        clock-names = "apb_pclk", "atclk";
        power-domains = <&cluster0_pd>;
    }

If funnel0 is bound to cluster's power domain, kernel's genPD will
automatically enable cluster power domain before access registers.

My understanding is your driver or firmware fails to turn on a cluster
power domain without waking up a CPU (and without sending IPI).  It is
not a kernel issue or limitation, and no any incorrect in PSCI OSI.

As Suzuki said, you might directly reply Sudeep's questions.  We would
confirm if any flaw in common code.

> > P.s., currently you can use "taskset" as a temporary solution without
> > any code change, something like:
> > 
> >   taskset -c 0 echo 1 > /sys/bus/coresight/devices/etm0/enable_source
> 
> This can address the runtime issue, but it does not resolve the problem during the probe phase.

Indeed.  If you insmod mode, you might can temporarily disable idle
states?

    exec 3<> /dev/cpu_dma_latency; echo 0 >&3
    insmod
    exec 3<>-

Thanks,
Leo