linux-kernel - Re: [PATCH v9 09/10] drm/doc: document some tracepoints as uAPI

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Message-ID: <27825c551adeda28f4b329f44c316ad2ab67fa5d.camel@mailbox.org>
Date: Wed, 14 May 2025 14:53:17 +0200
From: Philipp Stanner <phasta@...lbox.org>
To: Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer@....com>, David
 Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>, Maarten
 Lankhorst <maarten.lankhorst@...ux.intel.com>, Maxime Ripard
 <mripard@...nel.org>,  Thomas Zimmermann <tzimmermann@...e.de>, Jonathan
 Corbet <corbet@....net>, Matthew Brost <matthew.brost@...el.com>,  Danilo
 Krummrich <dakr@...nel.org>, Philipp Stanner <phasta@...nel.org>, Christian
 König <ckoenig.leichtzumerken@...il.com>, Sumit Semwal
 <sumit.semwal@...aro.org>
Cc: Lucas Stach <l.stach@...gutronix.de>, Maíra Canal
	 <mcanal@...lia.com>, Christian König
	 <christian.koenig@....com>, dri-devel@...ts.freedesktop.org, 
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-media@...r.kernel.org, linaro-mm-sig@...ts.linaro.org
Subject: Re: [PATCH v9 09/10] drm/doc: document some tracepoints as uAPI

On Thu, 2025-04-24 at 10:38 +0200, Pierre-Eric Pelloux-Prayer wrote:
> 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@...gutronix.de>
> Acked-by: Maíra Canal <mcanal@...lia.com>
> Reviewed-by: Christian König <christian.koenig@....com>
> Signed-off-by: Pierre-Eric Pelloux-Prayer
> <pierre-eric.pelloux-prayer@....com>
> ---
>  Documentation/gpu/drm-uapi.rst                | 19
> +++++++++++++++++++
>  .../gpu/drm/scheduler/gpu_scheduler_trace.h   | 19
> +++++++++++++++++++
>  2 files changed, 38 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 781b20349389..7e840d08ef39 100644
> --- a/drivers/gpu/drm/scheduler/gpu_scheduler_trace.h
> +++ b/drivers/gpu/drm/scheduler/gpu_scheduler_trace.h
> @@ -32,6 +32,25 @@
>  #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:
> + *
> + * * ``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
> + *
> + */

For my understanding, why do you use the double apostrophes here?

Also, the linking for the docu afair here two requires you to write

&struct dma_fence.seqno

If I am not mistaken

https://www.kernel.org/doc/html/latest/doc-guide/kernel-doc.html#highlights-and-cross-references


P.

> +
>  DECLARE_EVENT_CLASS(drm_sched_job,
>  	    TP_PROTO(struct drm_sched_job *sched_job, struct
> drm_sched_entity *entity),
>  	    TP_ARGS(sched_job, entity),