Now that framebuffer are reference-counted for all use-sites, update
the documentation accordingly to stress the new rules for
initialization and teardown.
Also add a short paragraph about the implications for drivers of the
new locking rules.
Signed-off-by: Daniel Vetter <daniel.vetter@xxxxxxxx>
---
Documentation/DocBook/drm.tmpl | 59 ++++++++++++++++++++++++++++++----------
1 file changed, 45 insertions(+), 14 deletions(-)
diff --git a/Documentation/DocBook/drm.tmpl b/Documentation/DocBook/drm.tmpl
index caab791..6c11d77 100644
--- a/Documentation/DocBook/drm.tmpl
+++ b/Documentation/DocBook/drm.tmpl
@@ -978,10 +978,25 @@ int max_width, max_height;</synopsis>
If the parameters are deemed valid, drivers then create, initialize and
return an instance of struct <structname>drm_framebuffer</structname>.
If desired the instance can be embedded in a larger driver-specific
- structure. The new instance is initialized with a call to
- <function>drm_framebuffer_init</function> which takes a pointer to DRM
- frame buffer operations (struct
- <structname>drm_framebuffer_funcs</structname>). Frame buffer operations are
+ structure. Drivers must fill its <structfield>width</structfield>,
+ <structfield>height</structfield>, <structfield>pitches</structfield>,
+ <structfield>offsets</structfield>, <structfield>depth</structfield>,
+ <structfield>bits_per_pixel</structfield> and
+ <structfield>pixel_format</structfield> fields from the values passed
+ through the <parameter>drm_mode_fb_cmd2</parameter> argument. They
+ should call the <function>drm_helper_mode_fill_fb_struct</function>
+ helper function to do so.
+ </para>
+
+ <para>
+ The initailization of the new framebuffer instance is finalized with a
+ call to <function>drm_framebuffer_init</function> which takes a pointer
+ to DRM frame buffer operations (struct
+ <structname>drm_framebuffer_funcs</structname>). Note that this function
+ publishes the framebuffer and so from this point on it can be accessed
+ concurrently from other threads. Hence it must be the last step in the
+ driver's framebuffer initialization sequence. Frame buffer operations
+ are
<itemizedlist>
<listitem>
<synopsis>int (*create_handle)(struct drm_framebuffer *fb,
@@ -1022,16 +1037,16 @@ int max_width, max_height;</synopsis>
</itemizedlist>
</para>
<para>
- After initializing the <structname>drm_framebuffer</structname>
- instance drivers must fill its <structfield>width</structfield>,
- <structfield>height</structfield>, <structfield>pitches</structfield>,
- <structfield>offsets</structfield>, <structfield>depth</structfield>,
- <structfield>bits_per_pixel</structfield> and
- <structfield>pixel_format</structfield> fields from the values passed
- through the <parameter>drm_mode_fb_cmd2</parameter> argument. They
- should call the <function>drm_helper_mode_fill_fb_struct</function>
- helper function to do so.
- </para>
+ The lifetime of a drm framebuffer is controlled with a reference count,
+ drivers can grab additional references with
+ <function>drm_framebuffer_reference</function> </para> and drop them
+ again with <function>drm_framebuffer_unreference</function>. For
+ driver-private framebuffers for which the last reference is never
+ dropped (e.g. for the fbdev framebuffer when the struct
+ <structname>drm_framebuffer</structname> is embedded into the fbdev
+ helper struct) drivers can manually clean up a framebuffer at module
+ unload time with
+ <function>drm_framebuffer_unregister_private</function>.
</sect2>
<sect2>
<title>Output Polling</title>
@@ -1043,6 +1058,22 @@ 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-<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 -->
--
1.7.10.4
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