linux-kernel - [PATCH v2 02/12] perf evsel: Support sparse fields in evsel__set_config_if

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Message-Id: <20251208-james-perf-config-bits-v2-2-4ac0281993b0@linaro.org>
Date: Mon, 08 Dec 2025 14:22:05 +0000
From: James Clark <james.clark@...aro.org>
To: 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>, 
 Suzuki K Poulose <suzuki.poulose@....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>, leo.yan@....com
Cc: linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org, 
 coresight@...ts.linaro.org, linux-arm-kernel@...ts.infradead.org, 
 James Clark <james.clark@...aro.org>
Subject: [PATCH v2 02/12] perf evsel: Support sparse fields in
 evsel__set_config_if_unset()

Sparse config fields are technically supported although currently
unused. field_prep() only works for contiguous bitfields so replace it
with pmu_format_value().

Signed-off-by: James Clark <james.clark@...aro.org>
---
 tools/perf/util/pmu.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/tools/perf/util/pmu.c b/tools/perf/util/pmu.c
index 956ea273c2c7..2c26c8d76bed 100644
--- a/tools/perf/util/pmu.c
+++ b/tools/perf/util/pmu.c
@@ -144,6 +144,8 @@ struct perf_pmu_format {
 };
 
 static int pmu_aliases_parse(struct perf_pmu *pmu);
+static void pmu_format_value(unsigned long *format, __u64 value, __u64 *v,
+			     bool zero);
 
 static struct perf_pmu_format *perf_pmu__new_format(struct list_head *list, char *name)
 {
@@ -1381,7 +1383,6 @@ bool evsel__is_aux_event(const struct evsel *evsel)
  * the bit pattern. It is shifted into position by this function, so to set
  * something to true, pass 1 for val rather than a pre shifted value.
  */
-#define field_prep(_mask, _val) (((_val) << (ffsll(_mask) - 1)) & (_mask))
 void evsel__set_config_if_unset(struct perf_pmu *pmu, struct evsel *evsel,
 				const char *config_name, u64 val)
 {
@@ -1398,8 +1399,7 @@ void evsel__set_config_if_unset(struct perf_pmu *pmu, struct evsel *evsel,
 		return;
 
 	/* Otherwise replace it */
-	evsel->core.attr.config &= ~bits;
-	evsel->core.attr.config |= field_prep(bits, val);
+	pmu_format_value(&bits, val, &evsel->core.attr.config, /*zero=*/true);
 }
 
 static struct perf_pmu_format *

-- 
2.34.1