coresight: etm4x: Expose default timestamp source in sysfs

Add a new sysfs interface in /sys/bus/coresight/devices/etm<N>/ts_source
indicating the configured timestamp source when the ETM device driver
was probed.

The perf tool will use this information to detect if the trace data
timestamp matches the kernel time, enabling correlation of CoreSight
trace with perf events.
Suggested-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: German Gomez <german.gomez@arm.com>
Reviewed-by: Leo Yan <leo.yan@linaro.org>
Signed-off-by: James Clark <james.clark@arm.com>
Link: https://lore.kernel.org/r/20220823160650.455823-2-james.clark@arm.comSigned-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>

arch/arm64/include/asm/sysreg.h

@@ -1021,6 +1021,7 @@
 #define SYS_MPIDR_SAFE_VAL	(BIT(31))
 
 #define TRFCR_ELx_TS_SHIFT		5
+#define TRFCR_ELx_TS_MASK		((0x3UL) << TRFCR_ELx_TS_SHIFT)
 #define TRFCR_ELx_TS_VIRTUAL		((0x1UL) << TRFCR_ELx_TS_SHIFT)
 #define TRFCR_ELx_TS_GUEST_PHYSICAL	((0x2UL) << TRFCR_ELx_TS_SHIFT)
 #define TRFCR_ELx_TS_PHYSICAL		((0x3UL) << TRFCR_ELx_TS_SHIFT)

drivers/hwtracing/coresight/coresight-etm4x-sysfs.c

@@ -2306,6 +2306,34 @@ static ssize_t cpu_show(struct device *dev,
 }
 static DEVICE_ATTR_RO(cpu);
 
+static ssize_t ts_source_show(struct device *dev,
+			      struct device_attribute *attr,
+			      char *buf)
+{
+	int val;
+	struct etmv4_drvdata *drvdata = dev_get_drvdata(dev->parent);
+
+	if (!drvdata->trfcr) {
+		val = -1;
+		goto out;
+	}
+
+	switch (drvdata->trfcr & TRFCR_ELx_TS_MASK) {
+	case TRFCR_ELx_TS_VIRTUAL:
+	case TRFCR_ELx_TS_GUEST_PHYSICAL:
+	case TRFCR_ELx_TS_PHYSICAL:
+		val = FIELD_GET(TRFCR_ELx_TS_MASK, drvdata->trfcr);
+		break;
+	default:
+		val = -1;
+		break;
+	}
+
+out:
+	return sysfs_emit(buf, "%d\n", val);
+}
+static DEVICE_ATTR_RO(ts_source);
+
 static struct attribute *coresight_etmv4_attrs[] = {
 	&dev_attr_nr_pe_cmp.attr,
 	&dev_attr_nr_addr_cmp.attr,
@@ -2360,6 +2388,7 @@ static struct attribute *coresight_etmv4_attrs[] = {
 	&dev_attr_vmid_val.attr,
 	&dev_attr_vmid_masks.attr,
 	&dev_attr_cpu.attr,
+	&dev_attr_ts_source.attr,
 	NULL,
 };