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author | Daniel Vetter <daniel.vetter@ffwll.ch> | 2017-03-02 16:16:38 +0100 |
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committer | Daniel Vetter <daniel.vetter@ffwll.ch> | 2017-03-14 15:13:37 +0100 |
commit | 4a8e2292874e57ab6245ee16a8048729423d289d (patch) | |
tree | ea02ec557ac3a0a0a31110dd62e5af41c3cd973c /Documentation/gpu/drm-kms.rst | |
parent | b2b82c26c7c1702cacde241cf63137eddd6524bf (diff) | |
download | linux-stable-4a8e2292874e57ab6245ee16a8048729423d289d.tar.gz linux-stable-4a8e2292874e57ab6245ee16a8048729423d289d.tar.bz2 linux-stable-4a8e2292874e57ab6245ee16a8048729423d289d.zip |
drm/doc: atomic overview, with graph
I want to split up a few more things and document some details better
(like how exactly to subclass drm_atomic_state). And maybe also split
up the helpers a bit per-topic, but this should be a ok-ish start for
better atomic overview.
v2: Spelling and clarifications (Eric).
v3: Implement suggestion from Gabriel to fix the graph.
v4: Review from Laurent.
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Gabriel Krisman Bertazi <krisman@collabora.co.uk>
Acked-by: Eric Anholt <eric@anholt.net>
Cc: Eric Anholt <eric@anholt.net>
Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Harry Wentland <harry.wentland@amd.com>
Reviewed-by: Gabriel Krisman Bertazi <krisman@collabora.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170302151638.1882-6-daniel.vetter@ffwll.ch
Diffstat (limited to 'Documentation/gpu/drm-kms.rst')
-rw-r--r-- | Documentation/gpu/drm-kms.rst | 84 |
1 files changed, 83 insertions, 1 deletions
diff --git a/Documentation/gpu/drm-kms.rst b/Documentation/gpu/drm-kms.rst index 1c42448c7aae..bfecd21a8cdf 100644 --- a/Documentation/gpu/drm-kms.rst +++ b/Documentation/gpu/drm-kms.rst @@ -189,8 +189,90 @@ multiple times to different objects using :c:func:`drm_object_attach_property() .. kernel-doc:: drivers/gpu/drm/drm_mode_object.c :export: +Atomic Mode Setting +=================== + + +.. kernel-render:: DOT + :alt: Mode Objects and Properties + :caption: Mode Objects and Properties + + digraph { + node [shape=box] + + subgraph cluster_state { + style=dashed + label="Free-standing state" + + "drm_atomic_state" -> "duplicated drm_plane_state A" + "drm_atomic_state" -> "duplicated drm_plane_state B" + "drm_atomic_state" -> "duplicated drm_crtc_state" + "drm_atomic_state" -> "duplicated drm_connector_state" + "drm_atomic_state" -> "duplicated driver private state" + } + + subgraph cluster_current { + style=dashed + label="Current state" + + "drm_device" -> "drm_plane A" + "drm_device" -> "drm_plane B" + "drm_device" -> "drm_crtc" + "drm_device" -> "drm_connector" + "drm_device" -> "driver private object" + + "drm_plane A" -> "drm_plane_state A" + "drm_plane B" -> "drm_plane_state B" + "drm_crtc" -> "drm_crtc_state" + "drm_connector" -> "drm_connector_state" + "driver private object" -> "driver private state" + } + + "drm_atomic_state" -> "drm_device" [label="atomic_commit"] + "duplicated drm_plane_state A" -> "drm_device"[style=invis] + } + +Atomic provides transactional modeset (including planes) updates, but a +bit differently from the usual transactional approach of try-commit and +rollback: + +- Firstly, no hardware changes are allowed when the commit would fail. This + allows us to implement the DRM_MODE_ATOMIC_TEST_ONLY mode, which allows + userspace to explore whether certain configurations would work or not. + +- This would still allow setting and rollback of just the software state, + simplifying conversion of existing drivers. But auditing drivers for + correctness of the atomic_check code becomes really hard with that: Rolling + back changes in data structures all over the place is hard to get right. + +- Lastly, for backwards compatibility and to support all use-cases, atomic + updates need to be incremental and be able to execute in parallel. Hardware + doesn't always allow it, but where possible plane updates on different CRTCs + should not interfere, and not get stalled due to output routing changing on + different CRTCs. + +Taken all together there's two consequences for the atomic design: + +- The overall state is split up into per-object state structures: + :c:type:`struct drm_plane_state <drm_plane_state>` for planes, :c:type:`struct + drm_crtc_state <drm_crtc_state>` for CRTCs and :c:type:`struct + drm_connector_state <drm_connector_state>` for connectors. These are the only + objects with userspace-visible and settable state. For internal state drivers + can subclass these structures through embeddeding, or add entirely new state + structures for their globally shared hardware functions. + +- An atomic update is assembled and validated as an entirely free-standing pile + of structures within the :c:type:`drm_atomic_state <drm_atomic_state>` + container. Again drivers can subclass that container for their own state + structure tracking needs. Only when a state is committed is it applied to the + driver and modeset objects. This way rolling back an update boils down to + releasing memory and unreferencing objects like framebuffers. + +Read on in this chapter, and also in :ref:`drm_atomic_helper` for more detailed +coverage of specific topics. + Atomic Mode Setting Function Reference -====================================== +-------------------------------------- .. kernel-doc:: include/drm/drm_atomic.h :internal: |