[PATCH v3 09/12] perf cs-etm: Don't use hard coded config bits when setting up ETMCR

James Clark
2025-12-12T15:33:02Z

Perf only looks at attr.config when determining what was programmed into
ETMCR. These bits could theoretically be in any of the config fields.
Add a generic helper to find the value of any named format field in any
config field and then use it to get the attributes relevant to ETMCR.

The kernel will also stop publishing the ETMCR register bits in a header
[1] so preempt that by defining them here.

Move field_prep() to util.h so we can define it along side field_get().
Unfortunately FIELD_PREP() and FIELD_GET() from the kernel can't be used
as they require the mask to be a compile time constant.

[1]: https://lore.kernel.org/linux-arm-kernel/20251128-james-cs-syncfreq-v8-10-4d319764cc58@linaro.org/
Signed-off-by: James Clark <james.clark@linaro.org>
---
tools/perf/arch/arm/util/cs-etm.c | 35 ++++++++++++++++++++++++++++++++++-
1 file changed, 34 insertions(+), 1 deletion(-)

diff --git a/tools/perf/arch/arm/util/cs-etm.c b/tools/perf/arch/arm/util/cs-etm.c
index 22c6272e8c367e5671809771b841c5babe2d5282..a5135b743e6f18789026323ea75b2a78d6495d73 100644
--- a/tools/perf/arch/arm/util/cs-etm.c
+++ b/tools/perf/arch/arm/util/cs-etm.c
@@ -68,6 +68,12 @@ static const char * const metadata_ete_ro[] = {

enum cs_etm_version { CS_NOT_PRESENT, CS_ETMV3, CS_ETMV4, CS_ETE };

+
+/* ETMv3 ETMCR register bits */
+#define ETMCR_CYC_ACC BIT(12)
+#define ETMCR_TIMESTAMP_EN BIT(28)
+#define ETMCR_RETURN_STACK BIT(29)
+
static bool cs_etm_is_ete(struct perf_pmu *cs_etm_pmu, struct perf_cpu cpu);
static int cs_etm_get_ro(struct perf_pmu *pmu, struct perf_cpu cpu, const char *path, __u64 *val);
static bool cs_etm_pmu_path_exists(struct perf_pmu *pmu, struct perf_cpu cpu, const char *path);
@@ -487,6 +493,33 @@ static int cs_etm_recording_options(struct auxtrace_record *itr,
return err;
}

+static u64 cs_etm_synth_etmcr(struct auxtrace_record *itr)
+{
+ struct cs_etm_recording *ptr =
+ container_of(itr, struct cs_etm_recording, itr);
+ struct perf_pmu *cs_etm_pmu = ptr->cs_etm_pmu;
+ struct evsel *evsel = cs_etm_get_evsel(ptr->evlist, cs_etm_pmu);
+ u64 etmcr = 0;
+ u64 val;
+
+ if (!evsel)
+ return 0;
+
+ /*
+ * Synthesize what the kernel programmed into ETMCR based on
+ * what options the event was opened with. This doesn't have to be
+ * complete or 100% accurate, not all bits used by OpenCSD anyway.
+ */
+ if (!evsel__get_config_val(cs_etm_pmu, evsel, "cycacc", &val) && val)
+ etmcr |= ETMCR_CYC_ACC;
+ if (!evsel__get_config_val(cs_etm_pmu, evsel, "timestamp", &val) && val)
+ etmcr |= ETMCR_TIMESTAMP_EN;
+ if (!evsel__get_config_val(cs_etm_pmu, evsel, "retstack", &val) && val)
+ etmcr |= ETMCR_RETURN_STACK;
+
+ return etmcr;
+}
+
static u64 cs_etm_get_config(struct auxtrace_record *itr)
{
struct cs_etm_recording *ptr =
@@ -746,7 +779,7 @@ static void cs_etm_get_metadata(struct perf_cpu cpu, u32 *offset,
case CS_ETMV3:
magic = __perf_cs_etmv3_magic;
/* Get configuration register */
- info->priv[*offset + CS_ETM_ETMCR] = cs_etm_get_config(itr);
+ info->priv[*offset + CS_ETM_ETMCR] = cs_etm_synth_etmcr(itr);
/* traceID set to legacy value in case new perf running on old system */
info->priv[*offset + CS_ETM_ETMTRACEIDR] = cs_etm_get_legacy_trace_id(cpu);
/* Get read-only information from sysFS */

--
2.34.1