On 24/01/2025 7:25 am, Jie Gan wrote:

The Coresight TMC Control Unit hosts miscellaneous configuration registers which control various features related to TMC ETR sink.

Based on the trace ID, which is programmed in the related CTCU ATID register of a specific ETR, trace data with that trace ID gets into the ETR buffer, while other trace data gets dropped.

Enabling source device sets one bit of the ATID register based on source device's trace ID. Disabling source device resets the bit according to the source device's trace ID.

Signed-off-by: Jie Gan quic_jiegan@quicinc.com

drivers/hwtracing/coresight/Kconfig | 12 + drivers/hwtracing/coresight/Makefile | 1 + drivers/hwtracing/coresight/coresight-ctcu.c | 276 +++++++++++++++++++ drivers/hwtracing/coresight/coresight-ctcu.h | 30 ++ include/linux/coresight.h | 3 +- 5 files changed, 321 insertions(+), 1 deletion(-) create mode 100644 drivers/hwtracing/coresight/coresight-ctcu.c create mode 100644 drivers/hwtracing/coresight/coresight-ctcu.h

[...]

+/*

• • ctcu_set_etr_traceid: Retrieve the ATID offset and trace ID.
• • Returns 0 indicates success. None-zero result means failure.
• */

+static int ctcu_set_etr_traceid(struct coresight_device *csdev, struct coresight_path *cs_path,

• 		bool enable)
  

+{

• struct coresight_device *sink = coresight_get_sink(cs_path->path);
• struct ctcu_drvdata *drvdata = dev_get_drvdata(csdev->dev.parent);
• u8 trace_id = cs_path->trace_id;
• int port_num;
• if ((sink == NULL) || !IS_VALID_CS_TRACE_ID(trace_id) || IS_ERR_OR_NULL(drvdata)) {

• dev_err(&csdev->dev, "Invalid parameters\n");
  

• return -EINVAL;
  

• }
• port_num = ctcu_get_active_port(sink, csdev);
• if (port_num < 0)

• return -EINVAL;
  

• /*

• * Skip the disable session if more than one TPDM device that
  

• * connected to the same TPDA device has been enabled.
  

• */
  

• if (enable)

• atomic_inc(&drvdata->traceid_refcnt[port_num][trace_id]);
  

• else {

• if (atomic_dec_return(&drvdata->traceid_refcnt[port_num][trace_id]) > 0) {
  

• 	dev_dbg(&csdev->dev, "Skip the disable session\n");
  

• 	return 0;
  

• }
  

• }
• dev_dbg(&csdev->dev, "traceid is %d\n", cs_path->trace_id);
• return __ctcu_set_etr_traceid(csdev, trace_id, port_num, enable);

Hi Jie,

Using atomic_dec_return() here doesn't prevent __ctcu_set_etr_traceid() from running concurrent enable and disables. Once you pass the atomic_dec_return() a second call to enable it will mess it up.

I think you need a spinlock around the whole thing and then the refcounts don't need to be atomics.