Re: [PATCH v3] coresight: tpdm: add traceid_show for checking traceid

James Clark
2026-03-30T14:56:11Z

On 25/03/2026 3:10 am, Jie Gan wrote:
> Save the trace ID in drvdata during TPDM enablement and expose it
> to userspace to support trace data parsing.
>
> The TPDM device’s trace ID corresponds to the trace ID allocated
> to the connected TPDA device.
>
> Signed-off-by: Jie Gan <jie.gan@oss.qualcomm.com>
> ---
> Changes in v3:
> 1. Only allow user to read the traceid while the TPDM device is enabled.
> - Link to v2: https://lore.kernel.org/r/20260316-add-traceid-show-for-tpdm-v2-1-1dec2a67e4ed@oss.qualcomm.com
>
> Changes in V2:
> 1. Use sysfs_emit instead of sprintf.
> Link to V1 - https://lore.kernel.org/all/20260306-add-traceid-show-for-tpdm-v1-1-0658a8edb972@oss.qualcomm.com/
> ---
> drivers/hwtracing/coresight/coresight-tpdm.c | 34 +++++++++++++++++++++++++++-
> drivers/hwtracing/coresight/coresight-tpdm.h | 2 ++
> 2 files changed, 35 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/hwtracing/coresight/coresight-tpdm.c b/drivers/hwtracing/coresight/coresight-tpdm.c
> index da77bdaad0a4..c8339b973bfc 100644
> --- a/drivers/hwtracing/coresight/coresight-tpdm.c
> +++ b/drivers/hwtracing/coresight/coresight-tpdm.c
> @@ -481,7 +481,7 @@ static void __tpdm_enable(struct tpdm_drvdata *drvdata)
>
> static int tpdm_enable(struct coresight_device *csdev, struct perf_event *event,
> enum cs_mode mode,
> - __maybe_unused struct coresight_path *path)
> + struct coresight_path *path)
> {
> struct tpdm_drvdata *drvdata = dev_get_drvdata(csdev->dev.parent);
>
> @@ -497,6 +497,7 @@ static int tpdm_enable(struct coresight_device *csdev, struct perf_event *event,
> }
>
> __tpdm_enable(drvdata);
> + drvdata->traceid = path->trace_id;
> drvdata->enable = true;
> spin_unlock(&drvdata->spinlock);
>
> @@ -693,6 +694,29 @@ static struct attribute_group tpdm_attr_grp = {
> .attrs = tpdm_attrs,
> };
>
> +static ssize_t traceid_show(struct device *dev,
> + struct device_attribute *attr, char *buf)
> +{
> + unsigned long val;
> + struct tpdm_drvdata *drvdata = dev_get_drvdata(dev->parent);
> +
> + if (coresight_get_mode(drvdata->csdev) == CS_MODE_DISABLED)
> + return -EINVAL;
> +
> + val = drvdata->traceid;

You probably need to take the coresight_mutex here otherwise you could
still return an invalid or stale value despite checking the mode.

There might also be some value in it returning the last used trace ID
even if the mode isn't enabled anymore. Because you can still read out
of the sink after disabling, so it makes more sense for a script to read
it at that point rather than when it's enabled. Also, you probably don't
want to be doing other things in your script in the point between
enabling and disabling.

> + return sysfs_emit(buf, "%#lx\n", val);
> +}
> +static DEVICE_ATTR_RO(traceid);
> +
> +static struct attribute *traceid_attrs[] = {
> + &dev_attr_traceid.attr,
> + NULL,
> +};
> +
> +static struct attribute_group traceid_attr_grp = {
> + .attrs = traceid_attrs,
> +};
> +
> static ssize_t dsb_mode_show(struct device *dev,
> struct device_attribute *attr,
> char *buf)
> @@ -1367,6 +1391,12 @@ static const struct attribute_group *tpdm_attr_grps[] = {
> &tpdm_cmb_patt_grp,
> &tpdm_cmb_msr_grp,
> &tpdm_mcmb_attr_grp,
> + &traceid_attr_grp,
> + NULL,
> +};
> +
> +static const struct attribute_group *static_tpdm_attr_grps[] = {
> + &traceid_attr_grp,
> NULL,
> };
>
> @@ -1425,6 +1455,8 @@ static int tpdm_probe(struct device *dev, struct resource *res)
> desc.access = CSDEV_ACCESS_IOMEM(base);
> if (res)
> desc.groups = tpdm_attr_grps;
> + else
> + desc.groups = static_tpdm_attr_grps;
> drvdata->csdev = coresight_register(&desc);
> if (IS_ERR(drvdata->csdev))
> return PTR_ERR(drvdata->csdev);
> diff --git a/drivers/hwtracing/coresight/coresight-tpdm.h b/drivers/hwtracing/coresight/coresight-tpdm.h
> index 2867f3ab8186..11da64e1ade8 100644
> --- a/drivers/hwtracing/coresight/coresight-tpdm.h
> +++ b/drivers/hwtracing/coresight/coresight-tpdm.h
> @@ -300,6 +300,7 @@ struct cmb_dataset {
> * @cmb Specifics associated to TPDM CMB.
> * @dsb_msr_num Number of MSR supported by DSB TPDM
> * @cmb_msr_num Number of MSR supported by CMB TPDM
> + * @traceid Trace ID of the path.
> */
>
> struct tpdm_drvdata {
> @@ -313,6 +314,7 @@ struct tpdm_drvdata {
> struct cmb_dataset *cmb;
> u32 dsb_msr_num;
> u32 cmb_msr_num;
> + u8 traceid;
> };
>
> /* Enumerate members of various datasets */
>
> ---
> base-commit: b84a0ebe421ca56995ff78b66307667b62b3a900
> change-id: 20260316-add-traceid-show-for-tpdm-88d040651f00
>
> Best regards,