linux-kernel - [PATCH] drm: Improve kerneldoc for drm_modeset

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Date:   Thu, 20 Jul 2017 17:07:48 +0100
From:   Liviu Dudau <Liviu.Dudau@....com>
To:     Daniel Vetter <daniel.vetter@...ll.ch>
Cc:     Jani Nikula <jani.nikula@...ux.intel.com>,
        Sean Paul <seanpaul@...omium.org>,
        David Airlie <airlied@...ux.ie>,
        DRI devel <dri-devel@...ts.freedesktop.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: [PATCH] drm: Improve kerneldoc for drm_modeset_lock

Explain better when the drm_modeset_acquire_ctx parameter can
be skipped for drm_modeset_lock() call.

Signed-off-by: Liviu Dudau <Liviu.Dudau@....com>
Cc: Daniel Vetter <daniel.vetter@...ll.ch>
---
 drivers/gpu/drm/drm_modeset_lock.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/drm_modeset_lock.c b/drivers/gpu/drm/drm_modeset_lock.c
index 64ef09a6cccb..af4e906c630d 100644
--- a/drivers/gpu/drm/drm_modeset_lock.c
+++ b/drivers/gpu/drm/drm_modeset_lock.c
@@ -52,7 +52,12 @@
  *     drm_modeset_drop_locks(&ctx);
  *     drm_modeset_acquire_fini(&ctx);
  *
- * On top of of these per-object locks using &ww_mutex there's also an overall
+ * If all that is needed is a single modeset lock, then the &struct
+ * drm_modeset_acquire_ctx is not needed and the locking can be simplified
+ * by passing a NULL instead of ctx in the drm_modeset_lock()
+ * call and, when done, by calling drm_modeset_unlock().
+ *
+ * On top of these per-object locks using &ww_mutex there's also an overall
  * &drm_mode_config.mutex, for protecting everything else. Mostly this means
  * probe state of connectors, and preventing hotplug add/removal of connectors.
  *
@@ -313,11 +318,14 @@ EXPORT_SYMBOL(drm_modeset_lock_init);
  * @lock: lock to take
  * @ctx: acquire ctx
  *
- * If ctx is not NULL, then its ww acquire context is used and the
+ * If @ctx is not NULL, then its ww acquire context is used and the
  * lock will be tracked by the context and can be released by calling
  * drm_modeset_drop_locks().  If -EDEADLK is returned, this means a
  * deadlock scenario has been detected and it is an error to attempt
  * to take any more locks without first calling drm_modeset_backoff().
+ *
+ * If @ctx is NULL then the function call behaves like a normal,
+ * non-nesting mutex_lock() call.
  */
 int drm_modeset_lock(struct drm_modeset_lock *lock,
 		struct drm_modeset_acquire_ctx *ctx)
-- 
2.13.2