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Date: Fri, 2 Oct 2026 18:14:05 +0100
From: Leo Yan <leo.yan@arm.com>
To: James Clark <james.clark@linaro.org>
Cc: John Garry <john.g.garry@oracle.com>, Will Deacon <will@kernel.org>,
	Mike Leach <mike.leach@arm.com>, Leo Yan <leo.yan@linux.dev>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Ingo Molnar <mingo@redhat.com>,
	Arnaldo Carvalho de Melo <acme@kernel.org>,
	Namhyung Kim <namhyung@kernel.org>,
	Mark Rutland <mark.rutland@arm.com>,
	Alexander Shishkin <alexander.shishkin@linux.intel.com>,
	Jiri Olsa <jolsa@kernel.org>, Ian Rogers <irogers@google.com>,
	Adrian Hunter <adrian.hunter@intel.com>,
	Suyash Mahar <smahar@meta.com>, Amir Ayupov <aaupov@fb.com>,
	Arnaldo Carvalho de Melo <acme@redhat.com>,
	linux-arm-kernel@lists.infradead.org, coresight@lists.linaro.org,
	linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3 3/4] perf cs-etm: Synthesize missing HW_ID mappings
 for raw trace
Message-ID: <20261002171405.GG1208404@e132581.arm.com>
References: <20261002-james-cs-hw_id-output-failure-v3-0-1d8b6ef339c8@linaro.org>
 <20261002-james-cs-hw_id-output-failure-v3-3-1d8b6ef339c8@linaro.org>
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In-Reply-To: <20261002-james-cs-hw_id-output-failure-v3-3-1d8b6ef339c8@linaro.org>

On Fri, Oct 02, 2026 at 12:15:13PM +0100, James Clark wrote:

[...]

>  static struct cs_etm_queue *cs_etm__get_queue(struct cs_etm_auxtrace *etm, int cpu)
> @@ -314,12 +317,11 @@ static int cs_etm__map_trace_id_v0(struct cs_etm_auxtrace *etm, u8 trace_chan_id
>  		return -EINVAL;
>  
>  	/*
> -	 * If the queue is unformatted then only save one mapping in the
> -	 * queue associated with that CPU so only one decoder is made.
> +	 * Ignore HW_IDs for unformatted, a decoder will be made
> +	 * unconditionally later.
>  	 */
>  	if (etmq->format == UNFORMATTED)
> -		return cs_etm__insert_trace_id_node(etmq, trace_chan_id,
> -						    cpu_metadata);
> +		return 0;

Nitpick: It seems to me that we can move the
etmq->format == UNFORMATTED check into cs_etm__process_aux_output_hw_id().

This avoids duplicating the check in both cs_etm__map_trace_id_v0()
and cs_etm__process_trace_id_v0_1(), and makes it more apparent that
the unformatted case does not use HW_ID at all.

It's up to you whether to keep it as is or update it. Either way:

Reviewed-by: Leo Yan leo.yan@arm.com

P.S. Although I contributed the initial idea, the change is now quite
different from the original patch I shared. Please feel free to drop my
name if you prefer.