linux-kernel - Re: [PATCH] coresight: docs: Remove target sink from examples

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Message-ID: <75ce4def-b0ca-428f-99a5-19ca98e876a0@os.amperecomputing.com>
Date: Thu, 12 Dec 2024 11:38:06 -0800
From: Steve Clevenger <scclevenger@...amperecomputing.com>
To: James Clark <james.clark@...aro.org>, coresight@...ts.linaro.org
Cc: yeoreum.yun@....com, Mike Leach <mike.leach@...aro.org>,
 Jonathan Corbet <corbet@....net>, Leo Yan <leo.yan@...ux.dev>,
 Namhyung Kim <namhyung@...nel.org>, linux-arm-kernel@...ts.infradead.org,
 linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] coresight: docs: Remove target sink from examples



On 12/12/2024 7:27 AM, James Clark wrote:
> 
> 
> On 11/12/2024 6:01 pm, Steve Clevenger wrote:
>>
>> Hi James,
>>
>> I thought I'd mention this issue with multicore self-hosted trace. The
>> perf command line syntax does not allow a sink "type" to be specified
>> (e.g. @tmc_etf or @tmc_etr). For multicore, it doesn't make sense to
>> specify a processor mapped sink as would be the case for single core
>> trace. A sink "type" should be allowed to avoid the auto select default.
>> In our case, the default is the ETF sink.
>>
>> Thanks,
>> Steve C.
>>
> 
> I'm sure it would be possible to add support for this, but I'm wondering
> if the real issue is that the default selection logic is wrong? Are you
> saying the default you get is ETF but you want ETR? And there is both
> for each ETM? The default selection logic isn't easy to summarize but it
> should prefer ETR (sysmem) over ETF (link sink), see coresight_find_sink().
> 
> It's probably better to fix that rather than add a new sink selection
> feature. Maybe if you shared a diagram of your coresight architecture it
> would help.
> 
> Thanks
> James

Hi James,

It appears the default sink selection is ETF for multicore trace. In any
case, for the Arm® CoreSight Base System Architecture STC Level
compliance, I need to be able to specify the sink type.

The Ampere CoreSight hierarchy is described to the ACPI as follows:


+-----------------+
|                 |
|       ETM       |
|                 |
+--------+--------+
         |
         |
+--------+--------+
|                 |
|       ETF       |
|                 |
+--------+--------+
         |
         |
+--------+--------+
|                 |
|       ETR       |
|                 |
+--------+--------+
         |
         |
+--------+--------+
|                 |
|      CATU       |
|                 |
+--------+--------+

Steve C.