On Mon, 15 Sept 2025 at 11:33, Leo Yan leo.yan@arm.com wrote:
As recommended in section 4.3.7 "Synchronization of register updates" of ARM IHI0064H.b, a self-hosted trace analyzer should always executes an ISB instruction after programming the trace unit registers.
An ISB works as a context synchronization event; a DSB is not required. Removes the redundant barrier in the enabling flow.
The ISB was placed at the end of the enable and disable functions. However, this does not guarantee a context synchronization event in the calling code, which may speculatively execute across function boundaries.
ISB instructions are moved into callers to ensure that a context synchronization is imposed immediately after enabling or disabling trace unit.
Fixes: 40f682ae5086 ("coresight: etm4x: Extract the trace unit controlling") Signed-off-by: Leo Yan leo.yan@arm.com
drivers/hwtracing/coresight/coresight-etm4x-core.c | 38 +++++++++++++++------- 1 file changed, 26 insertions(+), 12 deletions(-)
diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c b/drivers/hwtracing/coresight/coresight-etm4x-core.c index 382ec1a1cdd035e76d451d0112afd3f029ecbdb6..31d4838b47ae4a3a96c6a06774707214943268fc 100644 --- a/drivers/hwtracing/coresight/coresight-etm4x-core.c +++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c @@ -460,13 +460,6 @@ static int etm4_enable_trace_unit(struct etmv4_drvdata *drvdata) return -ETIME; }
/** As recommended by section 4.3.7 ("Synchronization when using the* memory-mapped interface") of ARM IHI 0064D*/dsb(sy);isb();return 0;}
@@ -581,6 +574,13 @@ static int etm4_enable_hw(struct etmv4_drvdata *drvdata)
if (!drvdata->paused) rc = etm4_enable_trace_unit(drvdata);
/** As recommended by section 4.3.7 (Synchronization of register updates)* of ARM IHI 0064H.b, the self-hosted trace analyzer always executes an* ISB instruction after programming the trace unit registers.*/isb();done: etm4_cs_lock(drvdata, csa);
@@ -956,11 +956,6 @@ static void etm4_disable_trace_unit(struct etmv4_drvdata *drvdata) if (etm4x_wait_status(csa, TRCSTATR_PMSTABLE_BIT, 1)) dev_err(etm_dev, "timeout while waiting for PM stable Trace Status\n");
/** As recommended by section 4.3.7 (Synchronization of register updates)* of ARM IHI 0064H.b.*/isb();}
static void etm4_disable_hw(struct etmv4_drvdata *drvdata) @@ -983,6 +978,13 @@ static void etm4_disable_hw(struct etmv4_drvdata *drvdata)
etm4_disable_trace_unit(drvdata);
/** As recommended by section 4.3.7 (Synchronization of register updates)* of ARM IHI 0064H.b, the self-hosted trace analyzer always executes an* ISB instruction after programming the trace unit registers.*/isb();/* read the status of the single shot comparators */ for (i = 0; i < drvdata->nr_ss_cmp; i++) { config->ss_status[i] =@@ -1120,6 +1122,12 @@ static int etm4_resume_perf(struct coresight_device *csdev)
etm4_cs_unlock(drvdata, csa); etm4_enable_trace_unit(drvdata);
/** As recommended by section 4.3.7 (Synchronization of register updates)* of ARM IHI 0064H.b, the self-hosted trace analyzer always executes an* ISB instruction after programming the trace unit registers.*/isb(); etm4_cs_lock(drvdata, csa); drvdata->paused = false;@@ -1136,6 +1144,12 @@ static void etm4_pause_perf(struct coresight_device *csdev)
etm4_cs_unlock(drvdata, csa); etm4_disable_trace_unit(drvdata);
/** As recommended by section 4.3.7 (Synchronization of register updates)* of ARM IHI 0064H.b, the self-hosted trace analyzer always executes an* ISB instruction after programming the trace unit registers.*/isb(); etm4_cs_lock(drvdata, csa); drvdata->paused = true;-- 2.34.1
Reviewed-by: Mike Leach mike.leach@linaro.org