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

Sudeep Holla
2025-12-19T10:07:00Z

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