[PATCH] coresight: fix trace ID search skipping pass-through NoC devices

[Jie Gan]

On 8/17/2026 4:50 PM, Jie Gan wrote:
> coresight_path_assign_trace_id() only treats a trace_id of 0 as "this
> device has no ID assignment, keep searching downstream". Pass-through
> NoC links such as itnoc (qcom,coresight-itnoc) intentionally return
> -EOPNOTSUPP from their .trace_id callback since they have no ATID
> register to program, but that negative value falls through to the
> IS_VALID_CS_TRACE_ID() check and is rejected, aborting the whole path
> with -EINVAL before the real trace ID owner further downstream is
> ever reached.
> 

Gentle reminder

> This breaks enabling any source whose path traverses an itnoc, e.g.
> writing 1 to tpdm/enable_source for a TPDM fails with:
> 
>    sh: write error: Invalid argument
> 
> Skip devices that return -EOPNOTSUPP the same way as devices that
> return 0, so the search continues to the next device on the path.
> 
> Fixes: f4526ffee6ff ("coresight: fix missing error code when trace ID is invalid")
> Signed-off-by: Jie Gan <jie.gan at oss.qualcomm.com>
> ---
>   drivers/hwtracing/coresight/coresight-core.c | 8 ++++++--
>   1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/hwtracing/coresight/coresight-core.c b/drivers/hwtracing/coresight/coresight-core.c
> index 6d65c43d574f..949ee9f00097 100644
> --- a/drivers/hwtracing/coresight/coresight-core.c
> +++ b/drivers/hwtracing/coresight/coresight-core.c
> @@ -953,8 +953,12 @@ int coresight_path_assign_trace_id(struct coresight_path *path,
>   		/* Assign a trace ID to the path for the first device that wants to do it */
>   		trace_id = coresight_get_trace_id(nd->csdev, mode, sink);
>   
> -		/* 0 means the device has no ID assignment, so keep searching */
> -		if (trace_id == 0)
> +		/*
> +		 * 0 means the device has no ID assignment, and -EOPNOTSUPP
> +		 * means the device explicitly declines to assign one (e.g. a
> +		 * pass-through NoC) - in both cases keep searching downstream.
> +		 */
> +		if (trace_id == 0 || trace_id == -EOPNOTSUPP)
>   			continue;
>   
>   		if (!IS_VALID_CS_TRACE_ID(trace_id))
> 
> ---
> base-commit: 4477a78374a57c3809b172ad30cceabda48c47c6
> change-id: 20260817-fix-trace-id-assign-issue-d269e90d1c62
> 
> Best regards,