On Wed, Nov 12, 2025 at 03:22:17PM +0000, James Clark wrote:
'timestamp' is currently 1 bit wide for on/off. To enable setting different intervals in a later commit, extend it to 4 bits wide. Keep the old bit position for backward compatibility but don't publish in the format/ folder. It will be removed from the documentation and can be removed completely after enough time has passed.
ETM3x doesn't support different intervals, so validate that the value is either 0 or 1.
Tools that read the bit positions from the format/ folder will continue to work as before, setting either 0 or 1 for off/on. Tools that incorrectly didn't do this and set the ETM_OPT_TS bit directly will also continue to work because that old bit is still checked.
This avoids adding a second timestamp attribute for setting the interval. This would be awkward to use because tools would have to be updated to ensure that the timestamps are always enabled when an interval is set, and the driver would have to validate that both options are provided together. All this does is implement the semantics of a single enum but spread over multiple fields.
Just a bit thoughts. My understanding is that the PMU format would clearly represent the PMU characteristics. I imagine that after reading the ETM specification, someone should be able to easily map to the PMU formats (enable field and counter field separately).
Alternatively, this patch provides a user-friendly interface that allows all settings (enable + counter) in one go. Users can benefit from it without knowing the underlying hardware mechanism, but might need to digest its semantics. As this will be well documented, I am fine for current approach:
Reviewed-by: Leo Yan leo.yan@arm.com
Signed-off-by: James Clark james.clark@linaro.org
drivers/hwtracing/coresight/coresight-etm-perf.h | 13 ++++++++++--- drivers/hwtracing/coresight/coresight-etm3x-core.c | 9 ++++++++- drivers/hwtracing/coresight/coresight-etm4x-core.c | 4 +++- 3 files changed, 21 insertions(+), 5 deletions(-)
diff --git a/drivers/hwtracing/coresight/coresight-etm-perf.h b/drivers/hwtracing/coresight/coresight-etm-perf.h index c794087a0e99..24d929428633 100644 --- a/drivers/hwtracing/coresight/coresight-etm-perf.h +++ b/drivers/hwtracing/coresight/coresight-etm-perf.h @@ -23,6 +23,9 @@ struct cscfg_config_desc; #define ATTR_CFG_FLD_preset_CFG config #define ATTR_CFG_FLD_preset_LO 0 #define ATTR_CFG_FLD_preset_HI 3 +#define ATTR_CFG_FLD_timestamp_CFG config +#define ATTR_CFG_FLD_timestamp_LO 4 +#define ATTR_CFG_FLD_timestamp_HI 7 #define ATTR_CFG_FLD_branch_broadcast_CFG config #define ATTR_CFG_FLD_branch_broadcast_LO 8 #define ATTR_CFG_FLD_branch_broadcast_HI 8 @@ -35,9 +38,13 @@ struct cscfg_config_desc; #define ATTR_CFG_FLD_contextid2_CFG config #define ATTR_CFG_FLD_contextid2_LO 15 #define ATTR_CFG_FLD_contextid2_HI 15 -#define ATTR_CFG_FLD_timestamp_CFG config -#define ATTR_CFG_FLD_timestamp_LO 28 -#define ATTR_CFG_FLD_timestamp_HI 28 +/*
- Old position of 'timestamp' and not published in sysfs. Remove at a later
- date if necessary.
- */
+#define ATTR_CFG_FLD_deprecated_timestamp_CFG config +#define ATTR_CFG_FLD_deprecated_timestamp_LO 28 +#define ATTR_CFG_FLD_deprecated_timestamp_HI 28 #define ATTR_CFG_FLD_retstack_CFG config #define ATTR_CFG_FLD_retstack_LO 29 #define ATTR_CFG_FLD_retstack_HI 29 diff --git a/drivers/hwtracing/coresight/coresight-etm3x-core.c b/drivers/hwtracing/coresight/coresight-etm3x-core.c index 584d653eda81..d4c04e563bf6 100644 --- a/drivers/hwtracing/coresight/coresight-etm3x-core.c +++ b/drivers/hwtracing/coresight/coresight-etm3x-core.c @@ -338,9 +338,16 @@ static int etm_parse_event_config(struct etm_drvdata *drvdata, if (ATTR_CFG_GET_FLD(attr, cycacc)) config->ctrl |= ETMCR_CYC_ACC;
- if (ATTR_CFG_GET_FLD(attr, timestamp))
- if (ATTR_CFG_GET_FLD(attr, deprecated_timestamp) ||
ATTR_CFG_GET_FLD(attr, timestamp))
- if (ATTR_CFG_GET_FLD(attr, timestamp) > 1) {
dev_dbg(&drvdata->csdev->dev,"timestamp format attribute should be 0 (off) or 1 (on)\n");return -EINVAL;- }
- /*
- Possible to have cores with PTM (supports ret stack) and ETM (never
- has ret stack) on the same SoC. So only enable when it can be honored
diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c b/drivers/hwtracing/coresight/coresight-etm4x-core.c index 1aa0357a5ce7..d4e294cd48ae 100644 --- a/drivers/hwtracing/coresight/coresight-etm4x-core.c +++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c @@ -28,6 +28,7 @@ #include <linux/amba/bus.h> #include <linux/seq_file.h> #include <linux/uaccess.h> +#include <linux/perf/arm_pmu.h> #include <linux/perf_event.h> #include <linux/perf/arm_pmu.h> #include <linux/platform_device.h> @@ -800,7 +801,8 @@ static int etm4_parse_event_config(struct coresight_device *csdev, cc_threshold = drvdata->ccitmin; config->ccctlr = cc_threshold; }
- if (ATTR_CFG_GET_FLD(attr, timestamp)) {
- if (ATTR_CFG_GET_FLD(attr, deprecated_timestamp) ||
ATTR_CFG_GET_FLD(attr, timestamp)) {
- Configure timestamps to be emitted at regular intervals in
- order to correlate instructions executed on different CPUs
-- 2.34.1