linux-kernel - Re: [PATCH 7/7] perf arm-spe: Don't hard code config attribute

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Message-ID: <20251202124240.GA724103@e132581.arm.com>
Date: Tue, 2 Dec 2025 12:42:40 +0000
From: Leo Yan <leo.yan@....com>
To: James Clark <james.clark@...aro.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Namhyung Kim <namhyung@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Jiri Olsa <jolsa@...nel.org>, Ian Rogers <irogers@...gle.com>,
	Adrian Hunter <adrian.hunter@...el.com>,
	Mike Leach <mike.leach@...aro.org>,
	John Garry <john.g.garry@...cle.com>, Will Deacon <will@...nel.org>,
	Leo Yan <leo.yan@...ux.dev>, linux-perf-users@...r.kernel.org,
	linux-kernel@...r.kernel.org, coresight@...ts.linaro.org,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 7/7] perf arm-spe: Don't hard code config attribute

On Tue, Dec 02, 2025 at 12:28:35PM +0000, Coresight ML wrote:
> On Mon, Dec 01, 2025 at 04:41:10PM +0000, Coresight ML wrote:
> > Use the config attribute that's published by the driver instead of
> > hard coding "attr.config".
> > 
> > Signed-off-by: James Clark <james.clark@...aro.org>
> > ---
> >  tools/perf/arch/arm64/util/arm-spe.c | 15 ++++++++-------
> >  1 file changed, 8 insertions(+), 7 deletions(-)
> > 
> > diff --git a/tools/perf/arch/arm64/util/arm-spe.c b/tools/perf/arch/arm64/util/arm-spe.c
> > index d5ec1408d0ae..6c3dc97fde30 100644
> > --- a/tools/perf/arch/arm64/util/arm-spe.c
> > +++ b/tools/perf/arch/arm64/util/arm-spe.c
> > @@ -256,7 +256,7 @@ static __u64 arm_spe_pmu__sample_period(const struct perf_pmu *arm_spe_pmu)
> >  
> >  static void arm_spe_setup_evsel(struct evsel *evsel, struct perf_cpu_map *cpus)
> >  {
> > -	u64 bit;
> > +	u64 pa_enable_bit;
> >  
> >  	evsel->core.attr.freq = 0;
> >  	evsel->core.attr.sample_period = arm_spe_pmu__sample_period(evsel->pmu);
> > @@ -288,9 +288,10 @@ static void arm_spe_setup_evsel(struct evsel *evsel, struct perf_cpu_map *cpus)
> >  	 * inform that the resulting output's SPE samples contain physical addresses
> >  	 * where applicable.
> >  	 */
> > -	bit = perf_pmu__format_bits(evsel->pmu, "pa_enable");
> > -	if (evsel->core.attr.config & bit)
> > -		evsel__set_sample_bit(evsel, PHYS_ADDR);
> > +
> > +	if (!evsel__get_config_val(evsel->pmu, evsel, "pa_enable", &pa_enable_bit))
> > +		if (pa_enable_bit)
> > +			evsel__set_sample_bit(evsel, PHYS_ADDR);
> 
> Hmm... I am a bit concerned for the evsel__get_config_val() usage
> throughout the series.
> 
> evsel__get_config_val() returns a whole config value rather than the
> bit field specified by the format name.  If other bits (but not the
> "pa_enable" bit) are set in the same config set, would it wrongly set
> the PHYS_ADDR sample bit?

I saw you used FIELD_GET() to read specific bit field in
evsel__get_config_val().  This is not concerned anymore.

Sorry for noise.

> Seems to me, for reading specific format, perf_pmu__format_bits() is
> more suitable than evsel__get_config_val().

For me, this comment is still valid, given perf_pmu__format_bits()
will always exist.

Thanks,
Leo