linux-kernel - Re: [PATCH v6 2/2] coresight: add coresight Trace Network On Chip driver

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Message-ID: <20250530125944.GB666854@e132581.arm.com>
Date: Fri, 30 May 2025 13:59:44 +0100
From: Leo Yan <leo.yan@....com>
To: Suzuki K Poulose <suzuki.poulose@....com>
Cc: Yuanfang Zhang <quic_yuanfang@...cinc.com>,
	Mike Leach <mike.leach@...aro.org>,
	James Clark <james.clark@...aro.org>, Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	kernel@....qualcomm.com, linux-arm-msm@...r.kernel.org,
	coresight@...ts.linaro.org, linux-arm-kernel@...ts.infradead.org,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 2/2] coresight: add coresight Trace Network On Chip
 driver

On Fri, May 30, 2025 at 12:32:23PM +0100, Suzuki Kuruppassery Poulose wrote:

[...]

> > > 2) How does the source driver know the TraceID for exposing via sysfs ?
> > > Does it expose its own traceid ?
> > No, sources connecting to TNOC don't have their own traceid, it expose the ATID which allocated in TNOC.
> > TNOC will maintain the ID in coresight_path:: trace_id, when enable source, the source can get it from path.
> > 
> > Here is the patch to expose id in source:
> > https://patchwork.kernel.org/project/linux-arm-kernel/patch/20250530-showtraceid-v1-1-2761352cf7b4@quicinc.com/
> 
> Please don't do that. We don't have to fake a traceid for all sources.
> It is only of use to the decoder, with manual input from the user. So,
> someone using the TNOC based system must be aware of how to collect the
> traceid and as such expose it from the TNOC and not all the other
> sources connected to it.
> 
> Simply expose it on the TNOC device node

[...]

> > > Good question, since we have the "path" maintaining the TraceID, we
> > > should use that here for the TNOC. But the other question is, can there be multiple sources connected to a single TNOC ? (I am guessing, yes!. And thus it may not work with what you are proposing.
> > > 
> > yes, there can be multiple sources connected to one TNOC, and these sources share one Trace ID which allocate in TNOC.
> > To decode the scenario relay on TraceID + Inport number, TraceID identifies the TNOC, the decoder maintains a table that maps each TNOC inport to its corresponding source.

If the Trace ID is only used to identify a TNOC, I am just wandering
if can use self-contained method.

For example, you can generate a ID number based on the register base
address, something like:

   /* TNOC physical address */
   drvdata->paddr = res->start;

   if (IS_ENABLED(CONFIG_PHYS_ADDR_T_64BIT))
       drvdata->atid = (drvdata->paddr >> 32) ^ (drvdata->paddr & 0xffffffffUL);
   else
       drvdata->atid = drvdata->paddr;

Then, you can get a unique ID for each TNOC in the system, and the
ID is determined by the pyshical address and can be calculated
directly by decoder.

Leo