Re: [PATCH 2/7] irqchip/irq-qcom-mpm: Register MPM under CPU cluster power domain

[Stephan Gerhold <stephan.gerhold@linaro.org>]

On Wed, Jul 15, 2026 at 11:46:58AM +0200, Konrad Dybcio wrote:
> On 7/13/26 12:25 PM, Sneh Mankad wrote:
> > MPM irqchip needs to notify RPM (Resource Power Manager) processor to read
> > the latest wake up capable interrupts when the CPU cluster is entering the
> > deepest idle state. This is done by sending IPC interrupt to RPM and is
> > implemented as .power_off() callback by registering MPM as parent power
> > domain to CPU cluster.
> 
> [...]
> 
> > If MPM has not registered with CPU cluster power domain, utilize the CPU PM
> > notifications to manage RPM communication when the last CPU goes to power
> > collapse.
> 
> I have mixed feelings about this case. The RPMH RSC driver keeps that as a
> fallback for platforms which don't have PSCI OSI mode specifically.
> 
> On the other hand, there are platforms (early arm64 - pre-msm8996 and almost
> all of the arm32 platforms) that don't define any CPU power domains, so
> perhaps it's necessary after all..
> 

I don't think this fallback is relevant for the non-PSCI QC platforms,
for the following reasons:

 - They don't define the MPM.
 - They don't support cluster idle upstream, so they don't need to
   define the MPM. They can't reach the idle state where it would become
   relevant.
 - The setup for cluster idle without PSCI is essentially equivalent to
   OSI, except that the SPM/SAW driver needs to program the idle state
   to enter. There is one SPM/SAW for every idle domain (e.g. on
   MSM8939: 2x4 CPU, 2x Cluster, 1x System). You can just model the
   SPM/SAW instances as power domains to get the same setup as PSCI OSI
   (I had a draft for this at some point). So if someone ever implements
   this, we should be able to use the same approach as for PSCI OSI.

I'm not aware of non-OSI PSCI platforms with MPM either, so I'm not sure
when this fallback would be used.

We probably do need some fallback for the old sm6375/agatii DTBs though.

Thanks,
Stephan