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authorVille Syrjälä <ville.syrjala@linux.intel.com>2020-07-17 16:54:39 +0300
committerVille Syrjälä <ville.syrjala@linux.intel.com>2020-07-24 21:20:55 +0300
commit6142b1b82ce43e6f7663f2e148ca48808f9d698f (patch)
tree71089087454921445ced87b90d23022997334b30 /Documentation/gpu
parent4031ead37239ec397fb9441555ae2d60e46dc333 (diff)
drm/todo: Plumb drm_atomic_state all over
Add a TODO for plumbing drm_atomic_state all over to ease the hurdles of accessing additional object states. Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch> #irc Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com> Link: https://patchwork.freedesktop.org/patch/msgid/20200717135439.5996-1-ville.syrjala@linux.intel.com
Diffstat (limited to 'Documentation/gpu')
-rw-r--r--Documentation/gpu/todo.rst46
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diff --git a/Documentation/gpu/todo.rst b/Documentation/gpu/todo.rst
index 7969f106877d..b0ea17da8ff6 100644
--- a/Documentation/gpu/todo.rst
+++ b/Documentation/gpu/todo.rst
@@ -403,6 +403,52 @@ Contact: Emil Velikov, respective driver maintainers
Level: Intermediate
+Plumb drm_atomic_state all over
+-------------------------------
+
+Currently various atomic functions take just a single or a handful of
+object states (eg. plane state). While that single object state can
+suffice for some simple cases, we often have to dig out additional
+object states for dealing with various dependencies between the individual
+objects or the hardware they represent. The process of digging out the
+additional states is rather non-intuitive and error prone.
+
+To fix that most functions should rather take the overall
+drm_atomic_state as one of their parameters. The other parameters
+would generally be the object(s) we mainly want to interact with.
+
+For example, instead of
+
+.. code-block:: c
+
+ int (*atomic_check)(struct drm_plane *plane, struct drm_plane_state *state);
+
+we would have something like
+
+.. code-block:: c
+
+ int (*atomic_check)(struct drm_plane *plane, struct drm_atomic_state *state);
+
+The implementation can then trivially gain access to any required object
+state(s) via drm_atomic_get_plane_state(), drm_atomic_get_new_plane_state(),
+drm_atomic_get_old_plane_state(), and their equivalents for
+other object types.
+
+Additionally many drivers currently access the object->state pointer
+directly in their commit functions. That is not going to work if we
+eg. want to allow deeper commit pipelines as those pointers could
+then point to the states corresponding to a future commit instead of
+the current commit we're trying to process. Also non-blocking commits
+execute locklessly so there are serious concerns with dereferencing
+the object->state pointers without holding the locks that protect them.
+Use of drm_atomic_get_new_plane_state(), drm_atomic_get_old_plane_state(),
+etc. avoids these problems as well since they relate to a specific
+commit via the passed in drm_atomic_state.
+
+Contact: Ville Syrjälä, Daniel Vetter
+
+Level: Intermediate
+
Core refactorings
=================