linux-kernel - Re: [PATCH RFC 1/3] coresight: tmc: add the handle of the event to the path

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Message-ID: <874isuo0m2.fsf@rasp.cworth.amperemail.amperecomputing.com>
Date: Mon, 22 Sep 2025 10:31:17 -0700
From: Carl Worth <carl@...amperecomputing.com>
To: Jie Gan <jie.gan@....qualcomm.com>, Suzuki K Poulose
 <suzuki.poulose@....com>, Mike Leach <mike.leach@...aro.org>, James Clark
 <james.clark@...aro.org>, Alexander Shishkin
 <alexander.shishkin@...ux.intel.com>, Jie Gan <jie.gan@....qualcomm.com>,
 Tingwei Zhang <tingwei.zhang@....qualcomm.com>
Cc: coresight@...ts.linaro.org, linux-arm-kernel@...ts.infradead.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC 1/3] coresight: tmc: add the handle of the event to
 the path

Jie Gan <jie.gan@....qualcomm.com> writes:
> From: Carl Worth <carl@...amperecomputing.com>
>
> The handle is essential for retrieving the AUX_EVENT of each CPU and is
> required in perf mode. It has been added to the coresight_path so that
> dependent devices can access it from the path when needed.

I'd still like to have the original command I used to trigger the bug in
the commit message. I really like having reproduction steps captured in
commit messages when I look back at commits in the future. So, that was:

	 perf record -e cs_etm//k -C 0-9 dd if=/dev/zero of=/dev/null

>  /**
>   * struct coresight_path - data needed by enable/disable path
> - * @path_list:              path from source to sink.
> - * @trace_id:          trace_id of the whole path.
> + * @path_list:			path from source to sink.
> + * @trace_id:			trace_id of the whole path.
> + * struct perf_output_handle:	handle of the aux_event.
>   */

Fixing to "@handle" was mentioned in another comment already.

Something about the above still feels a little off to me. It feels like
we're throwing new data into a structure just because it happens to be
conveniently at hand for the code paths we're needing, and not because
it really _belongs_ there.

Or, maybe it's the right place for it, and the cause of my concern is
that "path" is an overly-narrow name in struct coresight_path?

But if a renaming of this structure would improve the code, I'd also be
fine with that happening in a subsequent commit, so I won't try to hold
up the current series based on that.

-Carl