[PATCH v2 3/4] coresight: etm4x: Report the external outputs the PMU counts
Amir Ayupov
aaupov at fb.com
Mon Oct 12 16:05:22 PDT 2026
Some CPUs count the trace unit's external outputs as the PMU common
events TRCEXTOUT0-3 (0x4010-0x4013), which lets a configuration drive a
PMU event from trace unit events. Other CPUs, Neoverse N1 for example,
have no such events, and a feature relying on them would silently do
nothing there.
Detect at probe, on the trace unit's CPU, which outputs the PMU counts:
the trace unit has an external output for each of its events
(TRCIDR0.NUMEVENT), and from PMUv3p1, PMCEID0_EL0[63:32] reports which of
the common events 0x4000-0x401f are implemented. Per the ETE
specification, an implemented TRCEXTOUTn event counts external output n;
only whether that output is also an external input is IMPLEMENTATION
DEFINED.
Add a capability match flag for each output,
CS_CFG_MATCH_CAP_PMU_EXTOUT(n), set it on ETMs whose PMU counts that
output, and show it in the feature's configfs 'matches' attribute. With
capabilities matched separately from the device class, a feature that
requires one only loads on those ETMs.
Assisted-by: Devmate:Opus-5.5
Signed-off-by: Amir Ayupov <aaupov at fb.com>
---
.../hwtracing/coresight/coresight-config.h | 4 +++
.../hwtracing/coresight/coresight-etm4x-cfg.c | 5 ++-
.../coresight/coresight-etm4x-core.c | 32 +++++++++++++++++++
drivers/hwtracing/coresight/coresight-etm4x.h | 3 ++
.../coresight/coresight-syscfg-configfs.c | 7 ++++
5 files changed, 50 insertions(+), 1 deletion(-)
diff --git a/drivers/hwtracing/coresight/coresight-config.h b/drivers/hwtracing/coresight/coresight-config.h
index af6ef96b9ae01..10e95f5ecc8d9 100644
--- a/drivers/hwtracing/coresight/coresight-config.h
+++ b/drivers/hwtracing/coresight/coresight-config.h
@@ -35,6 +35,10 @@
* a device that matches one of its classes and has all of its capabilities.
*/
#define CS_CFG_MATCH_CAP_MASK 0x0000ff00
+/* trace unit external output n is countable by the PMU as TRCEXTOUTn */
+#define CS_CFG_MATCH_CAP_PMU_EXTOUT_SHIFT 8
+#define CS_CFG_MATCH_CAP_PMU_EXTOUT_NR 4 /* TRCEXTOUT0-3 */
+#define CS_CFG_MATCH_CAP_PMU_EXTOUT(n) BIT(CS_CFG_MATCH_CAP_PMU_EXTOUT_SHIFT + (n))
/* flags defining device instance matching - used in config match desc data. */
#define CS_CFG_MATCH_INST_ANY 0x80000000 /* any instance of a class */
diff --git a/drivers/hwtracing/coresight/coresight-etm4x-cfg.c b/drivers/hwtracing/coresight/coresight-etm4x-cfg.c
index e1a59b4345052..09a7a6b86968c 100644
--- a/drivers/hwtracing/coresight/coresight-etm4x-cfg.c
+++ b/drivers/hwtracing/coresight/coresight-etm4x-cfg.c
@@ -174,9 +174,12 @@ static int etm4_cfg_load_feature(struct coresight_device *csdev,
int etm4_cscfg_register(struct coresight_device *csdev)
{
+ struct etmv4_drvdata *drvdata = dev_get_drvdata(csdev->dev.parent);
struct cscfg_csdev_feat_ops ops;
+ u32 match_flags = CS_CFG_ETM4_MATCH_FLAGS;
ops.load_feat = &etm4_cfg_load_feature;
+ match_flags |= (u32)drvdata->pmu_extout << CS_CFG_MATCH_CAP_PMU_EXTOUT_SHIFT;
- return cscfg_register_csdev(csdev, CS_CFG_ETM4_MATCH_FLAGS, &ops);
+ return cscfg_register_csdev(csdev, match_flags, &ops);
}
diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c b/drivers/hwtracing/coresight/coresight-etm4x-core.c
index 2247ad55d4442..1e78774025d13 100644
--- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
+++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c
@@ -30,6 +30,7 @@
#include <linux/uaccess.h>
#include <linux/perf_event.h>
#include <linux/perf/arm_pmu.h>
+#include <linux/perf/arm_pmuv3.h>
#include <linux/platform_device.h>
#include <linux/pm_runtime.h>
#include <linux/property.h>
@@ -1368,6 +1369,35 @@ static void etm4_fixup_wrong_ccitmin(struct etmv4_drvdata *drvdata)
}
}
+/*
+ * Find the external outputs of this trace unit that the PMU counts as the
+ * common events TRCEXTOUT0-3. The trace unit has an external output for each
+ * of its events, and PMCEID0_EL0[63:32] reports the common events
+ * 0x4000-0x401f from PMUv3p1.
+ *
+ * Must run on the CPU that owns the trace unit.
+ */
+static u8 etm4_pmu_extout(struct etmv4_drvdata *drvdata)
+{
+ int pmuver = read_pmuver();
+ u64 pmceid;
+ u8 extout = 0;
+ int n;
+
+ if (!pmuv3_implemented(pmuver) || pmuver < ID_AA64DFR0_EL1_PMUVer_V3P1)
+ return 0;
+
+ pmceid = read_pmceid0() >> 32;
+ /* nr_event is TRCIDR0.NUMEVENT, the number of events minus one */
+ for (n = 0; n <= drvdata->nr_event; n++) {
+ if (pmceid & BIT_ULL(ARMV8_PMUV3_PERFCTR_TRCEXTOUT0 + n -
+ ARMV8_PMUV3_EXT_COMMON_EVENT_BASE))
+ extout |= BIT(n);
+ }
+
+ return extout;
+}
+
static void etm4_init_arch_data(void *info)
{
u32 etmidr0;
@@ -1522,6 +1552,8 @@ static void etm4_init_arch_data(void *info)
/* NUMCNTR, bits[30:28] number of counters available for tracing */
drvdata->nr_cntr = FIELD_GET(TRCIDR5_NUMCNTR_MASK, etmidr5);
+ drvdata->pmu_extout = etm4_pmu_extout(drvdata);
+
coresight_clear_self_claim_tag_unlocked(csa);
etm4_cs_lock(drvdata, csa);
cpu_detect_trace_filtering(drvdata);
diff --git a/drivers/hwtracing/coresight/coresight-etm4x.h b/drivers/hwtracing/coresight/coresight-etm4x.h
index df9e0748d71ec..11d95a4518b88 100644
--- a/drivers/hwtracing/coresight/coresight-etm4x.h
+++ b/drivers/hwtracing/coresight/coresight-etm4x.h
@@ -979,6 +979,8 @@ struct etmv4_save_state {
* @nrseqstate: The number of sequencer states that are implemented.
* @nr_seq_ctrls: The number of sequence state transition control registers.
* @nr_event: Indicates how many events the trace unit support.
+ * @pmu_extout: Bitmap of the external outputs n that the PMU counts as
+ * TRCEXTOUTn.
* @nr_resource:The number of resource selection pairs available for tracing.
* @nr_ss_cmp: Number of single-shot comparator controls that are available.
* @trcid: value of the current ID for this component.
@@ -1045,6 +1047,7 @@ struct etmv4_drvdata {
u8 nrseqstate;
u8 nr_seq_ctrls;
u8 nr_event;
+ u8 pmu_extout;
u8 nr_resource;
u8 nr_ss_cmp;
u8 trcid;
diff --git a/drivers/hwtracing/coresight/coresight-syscfg-configfs.c b/drivers/hwtracing/coresight/coresight-syscfg-configfs.c
index 2b40e556be872..7893d40f2e9ea 100644
--- a/drivers/hwtracing/coresight/coresight-syscfg-configfs.c
+++ b/drivers/hwtracing/coresight/coresight-syscfg-configfs.c
@@ -243,6 +243,7 @@ static ssize_t cscfg_feat_matches_show(struct config_item *item, char *page)
struct cscfg_fs_feature, group);
u32 match_flags = fs_feat->feat_desc->match_flags;
int used = 0;
+ int n;
if (match_flags & CS_CFG_MATCH_CLASS_SRC_ALL)
used = scnprintf(page, PAGE_SIZE, "SRC_ALL ");
@@ -250,6 +251,12 @@ static ssize_t cscfg_feat_matches_show(struct config_item *item, char *page)
if (match_flags & CS_CFG_MATCH_CLASS_SRC_ETM4)
used += scnprintf(page + used, PAGE_SIZE - used, "SRC_ETMV4 ");
+ for (n = 0; n < CS_CFG_MATCH_CAP_PMU_EXTOUT_NR; n++) {
+ if (match_flags & CS_CFG_MATCH_CAP_PMU_EXTOUT(n))
+ used += scnprintf(page + used, PAGE_SIZE - used,
+ "PMU_EXTOUT%d ", n);
+ }
+
used += scnprintf(page + used, PAGE_SIZE - used, "\n");
return used;
}
--
2.52.0
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