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

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Message-ID: <20251219-rugged-hamster-of-force-63bdc6@sudeepholla>
Date: Fri, 19 Dec 2025 10:06:52 +0000
From: Sudeep Holla <sudeep.holla@....com>
To: Suzuki K Poulose <suzuki.poulose@....com>
Cc: yuanfang zhang <yuanfang.zhang@....qualcomm.com>,
	Mike Leach <mike.leach@...aro.org>,
	Sudeep Holla <sudeep.holla@....com>,
	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 Thu, Dec 18, 2025 at 05:04:07PM +0000, Suzuki K Poulose wrote:
> On 18/12/2025 16:18, yuanfang zhang wrote:
> > 
> > On 12/18/2025 5:32 PM, Suzuki K Poulose wrote:
> > > Cc: Sudeep
> > > 
> > > On 18/12/2025 08:09, 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.
> > > > 
> > > > Unlike system-level CoreSight devices, these components share the CPU cluster's
> > > > power domain. When the cluster enters low-power mode (LPM), their registers
> > > > become inaccessible. Notably, `pm_runtime_get` alone cannot bring the cluster
> > > > out of LPM, making standard register access unreliable.
> > > 
> > > Why ? AFAIU, we have ways to tie the power-domain to that of the cluster
> > > and that can auto-magically keep the cluster power ON as long as you
> > > want to use them.
> > > 
> > > Suzuki
> > > 
> > Hi Suzuki
> > 
> > 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.
> 
> Why does it need to wake up the CPU ? The firmware can power up the
> cluster right? Anyways, to me this all looks like working around a
> firmware issue. I will let you sort this out with Sudeep's response
> , as I am not an expert on the cluster powermanagement and standards.
> 

Indeed smells like a some workaround, will respond in another email in the
thread to capture other points as well.

-- 
Regards,
Sudeep