Re: [PATCH v2 2/2] arm64: dts: qcom: kaanapali: fix traceNoC probe issue

[Jie Gan]

On 6/29/2026 10:28 PM, Leo Yan wrote:
> On Mon, Jun 29, 2026 at 10:08:17AM +0800, Jie Gan wrote:
>
> [...]
>
> > Can I fix the issue by adding "arm,primecell-periphid" property. That's
> > would be the best temp solution as it avoids breaking the original design of
> > both the TraceNoC AMBA driver and interconnect TraceNoC platform driver.
>
> Before proceeding with the "arm,primecell-periphid" property, could you
> clarify a bit:
>
>    - For an interconnect TraceNoC, what would be the consequence of
>      enabling ATID? Would it simply be a no-op, or are there any side
>      effects? Or is the concern that the trace IDs could be exhausted?

TPDM0(or ATB source) -> interconnect TraceNoC0 -> Aggregator TraceNoc -> 
sink
TPDM1(or ATB source) -> interconnect TraceNoC1 -> Aggregator TraceNoc -> 
sink

We only have one Aggregator TraceNoC and many interconnect TraceNoC 
devices for one platform. All interconnect TraceNoC devices are 
connected to Aggregator TraceNoC devices in the topology, so the itnoc 
doesnt need an ATID.

That's the design purpose from hardware perspective.


>    - How can you guarantee that a interconnect TraceNoC will never
>      require ATID in the future?

The interconnect TraceNoC is primarily introduced to reduce routing 
complexity in the hardware design. It is typically deployed as an 
intermediate TraceNoC that connects to an Aggregator TraceNoC (AG TraceNoC).

For example, a modem subsystem may contain many TPDM devices. Directly 
connecting every TPDM to the AG TraceNoC would result in significant 
wiring complexity. Instead, an itnoc is placed within the modem 
subsystem to locally aggregate the TPDM connections. All TPDMs first 
connect to the itnoc, and the itnoc then connects to the system-level AG 
TraceNoC.

From a hardware perspective, there is no fundamental difference between 
an itnoc and an AG TraceNoC. They use the same TraceNoC hardware 
implementation and share the same AMBA bus type. The distinction is 
purely functional: an itnoc is used for local trace aggregation within a 
subsystem, whereas an AG TraceNoC serves as the top-level aggregation 
point for the SoC.

Thanks,
Jie

> > The TraceNoC device here must be treated as an AMBA device and I am
> > continuing to investigate the issue with our hardware team.
>
> > We aim to fix it from hardware perspetive for existing platforms if possible
> > and ensure it is fixed in future platforms.
>
> I'm concerned that all of use end up repeatedly fixing similar issues
> whenever hardware configurations change or modules are reused in
> different topologies.
>
> For example, if future platforms may require ATID support for an
> interconnect TraceNoC, then the issue will pop up again.
>
> Thanks,
> Leo