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

[Jie Gan <jie.gan@oss.qualcomm.com>]

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.
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