[PATCH v5 4/4] 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.

Signed-off-by: Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer at amd.com>
---
 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 370d820be248..78496793a8f0 100644
--- a/Documentation/gpu/drm-uapi.rst
+++ b/Documentation/gpu/drm-uapi.rst
@@ -570,3 +570,22 @@ 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 the tracepoints documentation.
+In the drm subsystem, some events are considered stable uAPI to avoid
+breaking tools (eg: 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 0abcad26839c..63113803cdd5 100644
--- a/drivers/gpu/drm/scheduler/gpu_scheduler_trace.h
+++ b/drivers/gpu/drm/scheduler/gpu_scheduler_trace.h
@@ -33,6 +33,28 @@
 #define TRACE_SYSTEM gpu_scheduler
 #define TRACE_INCLUDE_FILE gpu_scheduler_trace
 
+
+/**
+ * DOC: uAPI trace events
+ *
+ * ``drm_sched_job``, ``drm_run_job``, ``drm_sched_process_job``,
+ * and ``drm_sched_job_wait_dep`` 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
+ *
+ */
+
 #ifndef __TRACE_EVENT_GPU_SCHEDULER_PRINT_FN
 #define __TRACE_EVENT_GPU_SCHEDULER_PRINT_FN
 /* Similar to trace_print_array_seq but for fences. */
-- 
2.40.1