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

From: Jie Gan

Date: Tue Jun 30 2026 - 04:47:46 EST

Hi Leo,

On 6/30/2026 4:10 PM, Leo Yan wrote:

Hi Jie,

On Tue, Jun 30, 2026 at 09:03:52AM +0800, Jie Gan wrote:

[...]

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

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.

I'm still not convinced that adding "arm,primecell-periphid" is the
right approach.

I agree we shouldn't need to add arm,primecell-periphid for the AMBA bus, as the hardware provides the necessary registers to read the peripheral ID. I used it as a temporary workaround to resolve the issue, but I believe that solution is not correct.

From the description above, I'd expect either the hardware to expose
bits in a register to distinguish these two module types, or as I
suggested earlier, to use a DT property to indicate the module type (or
whether ATID is required).

I wanna distinguish the aggregator traceNoC and interconnect traceNoC, even probe with platform driver, but the existing compatible is too specific to the interconnect traceNoC device(coresight-itnoc), that's why I didnt try the DT property proposal.

Or have you tried to detect the last tnoc on a path and allocate ID for
it? (You can retrieve csdev->path).

As Suzuki mentioned in the other thread, I think it would be better to add separate compatibles in the of_match_table to distinguish between Aggregator TraceNoC and Interconnect TraceNoC when probing with the platform driver. This would allow us to allocate an ATID only for Aggregator TraceNoC during probe, which is consistent with our original design.

Thanks,
Jie

Thanks,
Leo