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

[Jie Gan]

On 6/24/2026 9:51 PM, Suzuki K Poulose wrote:
> On 24/06/2026 14:48, Jie Gan wrote:
> > On 6/24/2026 9:27 PM, Konrad Dybcio wrote:
> > > On 6/24/26 11:49 AM, Jie Gan wrote:
> > > > The AMBA bus attempts to read the CID/PID of a device before invoking
> > > > its probe function if the arm,primecell-periphid property is absent.
> > > > This causes a deferred probe issue for the TraceNoC device, as the
> > > > CID/PID cannot be read from the periphid register.
> > >
> > > Why does it probe defer?
> >
> > For an AMBA device, the periphid is mandatory for probing. In the 
> > amba_match function, AMBA attempts to read the periphid from the CID/ 
> > PID registers if the arm,primecell-periphid property is absent in the 
> > device tree. If this read fails, it returns -EPROBE_DEFER, and the 
> > probe ultimately fails.
>
> Why does it fail ? power management ? hw broken ? Is it really AMBA or 
> do you pretend that to be an AMBA device by faking the CID/PID?

The CID reads as 0 from the register, which I suspect is a hardware 
design issue. I have not yet confirmed this with the hardware team. As a 
workaround, I provided a fake periphid via a DT property to bypass 
amba_read_periphid.


Leo commented in other thread:
>>tnoc.c registers both an AMBA driver and a platform driver. Shouldn't 
>>it
>>be registered as a platform device instead?

The platform driver is intended for the interconnect TraceNoC device and 
is not designed to allocate an ATID. The issue is that the TPDM device 
borrows the ATID from the TraceNoC device, resulting in the ATID always 
being 0 when associated with an interconnect NoC device.

However, I believe it is acceptable to allocate an ATID for the itNoC 
device and the issue can be fixed with this way.

Thanks,
Jie

> Suzuki
>
>
> > Most AMBA devices expose valid CID/PID registers, so specifying 
> > arm,primecell-periphid in the device tree is usually unnecessary. 
> > However, for the TraceNoC device in this case, AMBA cannot reliably 
> > read the periphid from the corresponding registers.
> >
> > > And is this required for all TNOC devices?
> >
> > So far, the TNOC device has been added to sm8750, Glymur, and 
> > Kaanapali platforms, and all exhibit probe failures due to the same 
> > root cause.
> >
> > I prefer to fix it on Kaanapali first.
> >
> > Thanks,
> > Jie
> >
> > > Konrad