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

[Suzuki K Poulose <suzuki.poulose@arm.com>]

On 30/06/2026 02:03, Jie Gan wrote:
> 
> 
> 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).


You can always distinguish one from the other by checking the
"compatibles"  or even add a custom data field to the of_device_id
table for the platform driver. Personally, I think it is better to
keep things away from AMBA framework, when we get everything from
platform driver.

Cheers
Suzuki


> 
> 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
>