[PATCH v8 08/10] drm/doc: document some tracepoints as uAPI

[Pierre-Eric Pelloux-Prayer]

This commit adds a document section in drm-uapi.rst about tracepoints,
and mark the events gpu_scheduler_trace.h as stable uAPI.

The goal is to explicitly state that tools can rely on the fields,
formats and semantics of these events.

Acked-by: Lucas Stach <l.stach@xxxxxxxxxxxxxx>
Acked-by: Maíra Canal <mcanal@xxxxxxxxxx>
Reviewed-by: Christian König <christian.koenig@xxxxxxx>
Signed-off-by: Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer@xxxxxxx>
---
 Documentation/gpu/drm-uapi.rst                | 19 ++++++++++++++++
 .../gpu/drm/scheduler/gpu_scheduler_trace.h   | 22 +++++++++++++++++++
 2 files changed, 41 insertions(+)

diff --git a/Documentation/gpu/drm-uapi.rst b/Documentation/gpu/drm-uapi.rst
index 69f72e71a96e..4863a4deb0ee 100644
--- a/Documentation/gpu/drm-uapi.rst
+++ b/Documentation/gpu/drm-uapi.rst
@@ -693,3 +693,22 @@ dma-buf interoperability
 
 Please see Documentation/userspace-api/dma-buf-alloc-exchange.rst for
 information on how dma-buf is integrated and exposed within DRM.
+
+
+Trace events
+============
+
+See Documentation/trace/tracepoints.rst for information about using
+Linux Kernel Tracepoints.
+In the DRM subsystem, some events are considered stable uAPI to avoid
+breaking tools (e.g.: GPUVis, umr) relying on them. Stable means that fields
+cannot be removed, nor their formatting updated. Adding new fields is
+possible, under the normal uAPI requirements.
+
+Stable uAPI events
+------------------
+
+From ``drivers/gpu/drm/scheduler/gpu_scheduler_trace.h``
+
+.. kernel-doc::  drivers/gpu/drm/scheduler/gpu_scheduler_trace.h
+   :doc: uAPI trace events
\ No newline at end of file
diff --git a/drivers/gpu/drm/scheduler/gpu_scheduler_trace.h b/drivers/gpu/drm/scheduler/gpu_scheduler_trace.h
index 4ce53e493fef..3c7f6a39cf91 100644
--- a/drivers/gpu/drm/scheduler/gpu_scheduler_trace.h
+++ b/drivers/gpu/drm/scheduler/gpu_scheduler_trace.h
@@ -32,6 +32,28 @@
 #define TRACE_SYSTEM gpu_scheduler
 #define TRACE_INCLUDE_FILE gpu_scheduler_trace
 
+/**
+ * DOC: uAPI trace events
+ *
+ * ``drm_sched_job_queue``, ``drm_sched_job_run``, ``drm_sched_job_add_dep``,
+ * ``drm_sched_job_done`` and ``drm_sched_job_unschedulable`` are considered
+ * stable uAPI.
+ *
+ * Common trace events attributes:
+ *
+ * * ``id``    - this is &drm_sched_job->id. It uniquely idenfies a job
+ *   inside a &struct drm_gpu_scheduler.
+ *
+ * * ``dev``   - the dev_name() of the device running the job.
+ *
+ * * ``ring``  - the hardware ring running the job. Together with ``dev`` it
+ *   uniquely identifies where the job is going to be executed.
+ *
+ * * ``fence`` - the &dma_fence.context and the &dma_fence.seqno of
+ *   &drm_sched_fence.finished
+ *
+ */
+
 DECLARE_EVENT_CLASS(drm_sched_job,
 	    TP_PROTO(struct drm_sched_job *sched_job, struct drm_sched_entity *entity),
 	    TP_ARGS(sched_job, entity),
-- 
2.43.0