linux-kernel - [PATCH] drm/sched: Document drm_sched_job

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Message-ID: <20240826093916.29065-2-pstanner@redhat.com>
Date: Mon, 26 Aug 2024 11:39:17 +0200
From: Philipp Stanner <pstanner@...hat.com>
To: Luben Tuikov <ltuikov89@...il.com>,
	Matthew Brost <matthew.brost@...el.com>,
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
	Maxime Ripard <mripard@...nel.org>,
	Thomas Zimmermann <tzimmermann@...e.de>,
	David Airlie <airlied@...il.com>,
	Daniel Vetter <daniel@...ll.ch>
Cc: dri-devel@...ts.freedesktop.org,
	linux-kernel@...r.kernel.org,
	Philipp Stanner <pstanner@...hat.com>
Subject: [PATCH] drm/sched: Document drm_sched_job_arm()'s effect on fences

The GPU Scheduler's job initialization is split into two steps,
drm_sched_job_init() and drm_sched_job_arm(). One reason for this is
that actually arming a job results in the job's fences getting
initialized (armed).

Currently, the documentation does not explicitly state what
drm_sched_job_arm() does in this regard and which rules the API-User has
to follow once the function has been called.

Add a section to drm_sched_job_arm()'s docstring which details the
function's consequences regarding the job's fences.

Signed-off-by: Philipp Stanner <pstanner@...hat.com>
---
 drivers/gpu/drm/scheduler/sched_main.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/gpu/drm/scheduler/sched_main.c b/drivers/gpu/drm/scheduler/sched_main.c
index 7e90c9f95611..e563eff4887c 100644
--- a/drivers/gpu/drm/scheduler/sched_main.c
+++ b/drivers/gpu/drm/scheduler/sched_main.c
@@ -831,6 +831,12 @@ EXPORT_SYMBOL(drm_sched_job_init);
  * Refer to drm_sched_entity_push_job() documentation for locking
  * considerations.
  *
+ * drm_sched_job_cleanup() can be used to disarm the job again - but only
+ * _before_ the job's fences have been published. Once a drm_sched_fence was
+ * published, the associated job needs to be submitted to and processed by the
+ * scheduler to avoid potential deadlocks on the DMA fences encapsulated by
+ * drm_sched_fence.
+ *
  * This can only be called if drm_sched_job_init() succeeded.
  */
 void drm_sched_job_arm(struct drm_sched_job *job)
-- 
2.46.0