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

[Jie Gan]

Hi Leo,

On 6/26/2026 6:30 PM, Leo Yan wrote:
> Hi Jie,
>
> On Fri, Jun 26, 2026 at 10:03:41AM +0800, Jie Gan wrote:
>
> [...]
>
> > Hi Leo,
> >
> > To be honest, I would prefer not to modify the interconnect platform driver.
> > On some Qualcomm platforms, multiple itnoc devices reside within small
> > blocks(one or more than one for each block) and are connected to a dummy
> > source. In such cases, two ATIDs are allocated for a path (the dummy source
> > and the itnoc), which is inefficient. This is why the itnoc platform driver
> > created to avoid this waste.
> >
> > The TraceNoC (called as AG TraceNoC) is a generic TraceNoC device which
> > connected to multiple source and link devices, aggregating data from all
> > source devices into a single output path.
>
> As I said, it may be fragile to couple a specific device property (ATID)
> to the AMBA driver.
>
> You're now facing a case where a device cannot be registered as an AMBA
> device, so it cannot use ATID. Likewise, I can imagine in future where a
> device is registered as an AMBA device, but you don't want ATID.

Agree. That's possible.

> > This device is implemented as an AMBA device but lacks proper hardware
> > configuration. As a result, it must be handled in the driver as a
> > workaround, which unfortunately breaks the original design intent.
>
> Seems to me, it is not reasonable to pretend an AMBA device but AMBA
> ID registers are absent.
>
> How about add a new DT property ("qcom,tnoc-enable-atid") to force
> enabling ATID?

That's a good proposal.

I have another proposal: what if we allocate the ATID in trace_noc_id() 
when the device does not already have a valid ATID?

Possible scenarios:

If the itnoc device is connected to a TPDM device (which has no ATID), 
trace_noc_id() will be invoked via coresight_path_assign_trace_id(), and 
a valid ATID can be allocated for the path.

If the itnoc device is connected to sources other than TPDM, 
trace_noc_id() will never be invoked, and therefore no ATID will be 
allocated for the device, saving resources.

Thanks,
Jie

> Thanks,
> Leo