Re: [PATCH] drm/doc: Unify KMS Locking docs

[Daniel Vetter <daniel@ffwll.ch>]

On Mon, May 30, 2016 at 11:10:49AM +0200, Daniel Vetter wrote:
> Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>

Merged with Jani's irc-ack - we want to get all things docbook merged
before the big sphinx conversion happens.
-Daniel

> ---
>  Documentation/DocBook/gpu.tmpl     | 16 ----------------
>  drivers/gpu/drm/drm_modeset_lock.c | 11 +++++++++--
>  2 files changed, 9 insertions(+), 18 deletions(-)
> 
> diff --git a/Documentation/DocBook/gpu.tmpl b/Documentation/DocBook/gpu.tmpl
> index d755d53615d7..cb130514cedf 100644
> --- a/Documentation/DocBook/gpu.tmpl
> +++ b/Documentation/DocBook/gpu.tmpl
> @@ -1092,22 +1092,6 @@ int max_width, max_height;</synopsis>
>          operation.
>        </para>
>      </sect2>
> -    <sect2>
> -      <title>Locking</title>
> -      <para>
> -        Beside some lookup structures with their own locking (which is hidden
> -	behind the interface functions) most of the modeset state is protected
> -	by the <code>dev-&lt;mode_config.lock</code> mutex and additionally
> -	per-crtc locks to allow cursor updates, pageflips and similar operations
> -	to occur concurrently with background tasks like output detection.
> -	Operations which cross domains like a full modeset always grab all
> -	locks. Drivers there need to protect resources shared between crtcs with
> -	additional locking. They also need to be careful to always grab the
> -	relevant crtc locks if a modset functions touches crtc state, e.g. for
> -	load detection (which does only grab the <code>mode_config.lock</code>
> -	to allow concurrent screen updates on live crtcs).
> -      </para>
> -    </sect2>
>    </sect1>
>  
>    <!-- Internals: kms initialization and cleanup -->
> diff --git a/drivers/gpu/drm/drm_modeset_lock.c b/drivers/gpu/drm/drm_modeset_lock.c
> index e3a4adf03e7b..f33ebe638a28 100644
> --- a/drivers/gpu/drm/drm_modeset_lock.c
> +++ b/drivers/gpu/drm/drm_modeset_lock.c
> @@ -30,12 +30,12 @@
>   *
>   * As KMS moves toward more fine grained locking, and atomic ioctl where
>   * userspace can indirectly control locking order, it becomes necessary
> - * to use ww_mutex and acquire-contexts to avoid deadlocks.  But because
> + * to use &ww_mutex and acquire-contexts to avoid deadlocks.  But because
>   * the locking is more distributed around the driver code, we want a bit
>   * of extra utility/tracking out of our acquire-ctx.  This is provided
>   * by drm_modeset_lock / drm_modeset_acquire_ctx.
>   *
> - * For basic principles of ww_mutex, see: Documentation/locking/ww-mutex-design.txt
> + * For basic principles of &ww_mutex, see: Documentation/locking/ww-mutex-design.txt
>   *
>   * The basic usage pattern is to:
>   *
> @@ -51,6 +51,13 @@
>   *     ... do stuff ...
>   *     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
> + *  dev->mode_config.lock, for protecting everything else. Mostly this means
> + *  probe state of connectors, and preventing hotplug add/removal of connectors.
> + *
> + *  Finally there's a bunch of dedicated locks to protect drm core internal
> + *  lists and lookup data structures.
>   */
>  
>  /**
> -- 
> 2.8.1
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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